A genotype is the genetic make up of an individual Pearson - BIO - 1100 View Full Document Name ______Bennett_ ____ Page 2 of 7 Heredity 4. Explain Mendel’s “law” of “independent assortment”. When does it occur during cell division? Mendel’s law of independent assortment states that each pair of factors assorts independently of the other pairs and that all possible combinations of factors can occur in the gametes. (Mader and Windelspecht) This means that the genes from one trait separate independently from the genes of another trait allowing for multiple different outcomes. Independent assortment occurs in meiosis I, specifically in prophase I. 5. Explain Mendel’s “law” of “segregation”. Give an example. Mendel’s law of segregation states that each individual has two factors for each trait and that these factors separate during the formation of gametes. Each gamete then contains only one gene from each pair of genes. Fertilization then gives each new individual two genes for each trait.

(Mader and Windelspecht) An example of the law of segregation is shown in the lab when the genes from a tall pea plant are combined with the genes of a dwarf pea plant resulting in the separation of the gametes and allowing for either a tall pea plant or dwarf pea plant as offspring. Genetics Problem Involving a Monohybrid Cross Possible Points 4 Points Deducted Add a row or column to the tables if necessary. 6. A plant that is heterozygous (Pp) for purple flowers is crossed with a plant that is also heterozygous (Pp) for purple flowers. What will be the genotypes and phenotypes of the F 1 generation? Type the possible gene combinations in the Punnett square and then type the genotype and phenotype ratios in the table below the Punnett square.

P = purple flowers (dominant) p = white flowers (recessive) P p P PP Pp p Pp pp Genotypes Phenotypes of Flower Colors # of Each Phenotype (data taken from Punnett square) Ratios of Phenotypes PP Homozygous dominant 1 1:4 Purple flowers Purple flowers Name ______Bennett_ ____ Page 3 of 7 Heredity Pp Heterozygous 2 1:2 pp Homozygous recessive 1 1:4 Testcross Problem to Determine Unknown Genotypes Possible Points 4 Points Deducted Add a row or column to the tables if necessary. 7. This preview has intentionally blurred sections. Sign up to view the full version. Genotype and phenotype | Sciencelearn Hub Genotype and phenotype Video: Researching the link between genotype and phenotype We are all unique. Even monozygotic twins , who are genetically identical, always have some variation in the way they look and act. This uniqueness is a result of the interaction between our genetic make-up, inherited from our parents, and environmental influences from the moment we are conceived.

Understanding genotype and phenotype Wilhelm Johannsen was a scientist working in Denmark in the late 19th and early 20th centuries. During a series of experiments, he observed variations in genetically identical beans. He concluded the variation must be due to environmental factors and coined the terms ‘ genotype ’ and ‘ phenotype ’ in 1911. Genotype is the genetic make-up of an individual organism . Your genotype functions as a set of instructions for the growth and development of your body. The word ‘genotype’ is usually used when talking about the genetics of a particular trait (like eye colour). Phenotype is the observable physical or biochemical characteristics of an individual organism, determined by both genetic make-up and environmental influences, for example, height, weight and skin colour. How genotype affects phenotype The term ‘genotype’ is usually used to refer to specific alleles. Alleles are alternative forms of the same gene that occupy the same location on a chromosome . At any given locus , there are 2 alleles (1 on each chromosome in the pair) – you get 1 allele from your mother and 1 from your father. The 2 alleles might be the same or they might be different.

Different alleles of a gene generally serve the same function (for example, they code for a protein that affects eye colour) but may produce different phenotypes (for example, blue eyes or brown eyes) depending on which set of 2 alleles you have. For example, the ability to taste PTC (a bitter tasting compound ) is controlled by a single gene. This gene has at least 7 alleles but only 2 of these are commonly found. An upper case ‘T’ represents the dominant allele that confers the ability to taste – ‘dominant’ means that anyone with 1 or 2 copies of this allele will be able to taste PTC. The non-tasting allele is recessive and is represented by a lower case ‘t’ – ‘recessive’ means that an individual will need 2 copies of the allele to be a non-taster. Each pair of alleles represents the genotype of a specific individual, and in this case, there are 3 possible genotypes: TT (taster), Tt (taster) and tt (non-taster). If the alleles are the same (TT or tt), the genotype is homozygous. If the alleles are different (Tt) the genotype is heterozygous.

It is actually rare that 1 gene determines 1 characteristic as in the case of PTC tasting (a monogenic trait). Most traits are complex and have genes that affect them at more than 1 locus (polygenic). How environmental factors affect phenotype Video: Genetics or environment Your genes carry the instructions for the growth and development of your body. However, your phenotype is influenced during embryonic development and throughout your life by environmental factors. Environmental factors are many and varied and include diet, climate, illness and stress. With the PTC tasting example, scientists estimate that the gene controls about 85% of the ability to taste. Environmental factors that play a role include how dry your mouth is or how recently you have eaten. The degree to which your phenotype is determined by your genotype is referred to as ‘phenotypic plasticity’. If environmental factors have a strong influence, the phenotypic plasticity is high. If genotype can be used to reliably predict phenotype, the phenotypic plasticity is low. Overall, the amount of influence that environmental factors have on your ultimate phenotype is a hotly debated scientific issue. It is often referred to as the ‘nature (genes) versus nurture (environment)’ debate.

Scientists commonly study monozygous (identical) twins to investigate the genotype/phenotype relationship. In conclusion, your genotype or genetic make-up plays a critical role in your development. However, environmental factors influence our phenotypes throughout our lives, and it is this on-going interplay between genetics and environment that makes us all unique. Useful links Chapter 29 Heredity Exam Flashcards | Easy Notecards B) a dominant genetic disorder C) a sex-linked genetic disorder D) a recessive genetic disorder Answer: A 11) An example of multiple allele inheritance is ________. A) the ABO blood group B) the appearance of freckles on the skin C) the appearance of birthmarks on the skin D) hair that seems to have several shades of a color Answer: A 12 12) Which of the following is true concerning environmental influence on genetic expression? A) It is impossible to alter in any way the expression of a gene in humans. B) The only time a gene can be influenced by environmental factors is in the second trimester of the pregnancy. 25) One possible scientific explanation for siblings having very different skin color is ________.

A) polygene inheritance, which results in continuous phenotypic variation between extremes B) that some people may be in the sun longer than others C) that the gene for dark skin is dominant over the gene for light skin, and some offspring inherit chromosomes with one of each allele D) There is no explanation for the variation Answer: A 26) Which of the following statements is true concerning screening? A) Screening is illegal in over half of the world. B) Screening can be done only in the first trimester of pregnancy. C) Genetic screening is rarely done because it yields very little accurate information. D) Screening can be done before conception by carrier recognition or during fetal testing. Answer: D 1) The X and Y chromosomes are considered the ________ chromosomes. Answer: sex 2) An allele that completely masks the expression of the other alleles is called ________. Answer: dominant 3) Observable characteristics expressed by the genes for a trait are called the ________. Answer: phenotype 4) Albinism is a good example of a ________ trait. Answer: recessive 5) Color blindness is a ________ trait.

Answer: sex-linked 39 6) Removing a sample of the fluid surrounding the fetus for the purpose of studying the chromosomes is a procedure called ________. Answer: amniocentesis 7) The 23rd pair of human chromosomes are called ________ chromosomes. Answer: sex 8) The ABO blood type is a good example of a ________ inheritance. Answer: multiple-allele Answer: Karyotype is the chromosomal content of a cell. 44 11) How might carriers of deleterious genes be recognized? Answer: Carriers of deleterious genes may be recognized if their offspring show symptoms of the condition or disease caused by the deleterious gene. Because the genes are usually recessive, they would show only phenotypically if the offspring received the recessive genes from both parents. A pedigree analysis may be done to trace a particular trait back through several generations. Blood chemistry tests (and DNA probing) may also be done if particular genetic traits are suspected. 45 12) ________ disease is a disorder of brain lipid metabolism and is an example of a recessive trait.

Answer: Tay-Sachs 46 13) When both parents are heterozygous for a recessive trait, they run a one-in-four chance that the ________ trait will be expressed in their children. Answer: recessive Using Figure 29.2, match the following: 14) Is the trait sex-linked? Answer: Yes. 15) Is the trait dominant or recessive? Answer: Recessive. 16) Identify, by numbers, any known carriers. Answer: 2, 5, 7, and 18. 50 17) Identify, by numbers, any other possible carriers. Answer: 9, 14, 16, 23, and 25. 51 18) Are there any afflicted females? Answer: No. 19) Are there any male carriers? Answer: No. 20) When might amniocentesis be appropriate? Answer: Amniocentesis might be performed any time a history of any genetic disability is discovered in a family, especially if there are several occurrences in a family. This will give the parents an early warning of any possible problem with the fetus.

Other ʺhigh-risk pregnanciesʺ (e.g. women over 35) may also suggest use of amniocentesis. 54 21) Describe briefly the three mechanisms that lead to genetic variability. Answer: The three mechanisms that lead to genetic variability include independent assortment of chromosomes, crossover of homologues, and random fertilization of eggs by sperm. Each pair of homologous chromosomes synapses during meiosis I, forming a tetrad. The alignment and orientation of the tetrads on the metaphase I spindle depend on chance. The chromosomes are then randomly distributed to daughter cells. Because the way each tetrad aligns is random, and many mother cells are undergoing meiosis simultaneously, each alignment and each type of gamete occurs with the same frequency as all others. Additional variation results from the crossing over and exchange of chromosomal parts that occur during meiosis I. During meiosis, paternal chromosomes can precisely exchange gene segments with the homologous maternal ones, giving rise to recombinant chromosomes with mixed contributions from each parent. A single human egg will be fertilized by a single sperm on a totally haphazard basis.

Answer: The second-generation, fuzzy-longhaired individuals could be FFTT, FfTT, FFTt, or FfTt. 30) What were the genotypes of the parental (P1) individuals? Answer: The genotypes of the parental individuals were FFTT and fftt. 64 31) Two tall red pea plants, when crossed, produced some offspring that were white and dwarf. Assuming that tallness and redness are dominant, what are the genotypes of the parents? Answer: The parents must both be heterozygous for the dominant traits; therefore, their genotypes would be TtRr, where T = dominant trait for height, t = recessive trait for height, R = dominant trait for color, and r = recessive trait for color. 65 Clinical Questions 1) In humans, farsightedness is inherited by possession of a dominant gene. If a man who is homozygous for normal vision (aa) marries a woman who is heterozygous for farsightedness, what proportion of their children would be expected to be farsighted? Answer: One-half of their children would be expected to be farsighted.

66 2) Parents are informed after an amniocentesis that the results show a baby who has an extra number 21 chromosome. Should there be concern and what might the problem be? Answer: The fetus will become a Down syndrome baby. The baby will probably be retarded, have short fingers and a large tongue, and have a tendency for a short stature. 67 3) Jane and Allen have just discovered that their son is a hemophiliac. Neither of them has hemophilia, and Allen claims that no such condition was ever expressed in his family. Jane was told that her father was a hemophiliac and that problems resulting from this condition caused his death. Allen has also been told that hemophilia can only be passed on to an offspring by parents and not by grandparents; he believes that Jane was unfaithful and that the child is not his. If you were a genetic counselor, what would you tell Allen? Answer: The grandfather of the child was a hemophiliac and gave his X chromosome to Jane. She did not express the disease because she has two X chromosomes, and the normal dominant allele suppressed the expression of hemophilia (a male needs only one hemophiliac allele to express the disease).

Jane was not unfaithful, as she is a carrier who would not be expected to express the recessive phenotype. The child probably received the allele from Jane even though she did not have the disease 68 4) The folk singer, Woody Guthrie, died of Huntingtonʹs chorea. One of his parents also died of this disease affecting the nervous system. The disease usually affects carriers between 25 and 45 years of age and is inherited as a Mendelian autosomal dominant trait. Using Punnett squares, determine the probability that any of the three Guthrie offspring will have this devastating disease. Answer: Woody had to have been a heterozygote Hh for the allele because the dominant homozygous condition is lethal to the fetus. Woodyʹs wife did not have the disease so she was not carrying it. Genetically they were Hh × hh. Using a Punnett square, the probability of having a child with the disease would be 50%. 69 5) A 40-year-old pregnant woman is concerned about possible genetic defects in her unborn fetus. Her physician recommends prenatal testing and advises her of two methods.

Compare and contrast amniocentesis with chorionic villi sampling relative to the time each can be performed, and the relative advantages and disadvantages of each. Answer: Amniocentesis is not normally done before the 14th week of pregnancy. The disadvantage is the risk of injury to the fetus, but ultrasound visualization has dramatically reduced the risk. Tests can be done on the fluid withdrawn to determine the presence of chemicals that serve as markers for specific diseases. The cells themselves are cultured and examined for DNA markers of genetic disease. Karyotyping is also done to check for chromosomal abnormalities. Chorionic villi sampling can be done at eight weeks. It is much faster but may be more risky for the fetus. Karyotyping can be done on the rapidly dividing cells very quickly. 70 6) A family has four offspring belonging respectively to ABO blood groups A, B, O, and AB. Give the genotypes and phenotypes of the parents. Answer: The parents have the following genotypes and phenotypes: One parent is IAi (heterozygous for A) with type A blood; the other parent is IBi (heterozygous for B) with type B blood.

71 7) Assume that the allele controlling brown eyes (B) is dominant over that controlling blue eyes (b) in human beings. (In actuality, eye color in humans is an example of polygene inheritance, which is much more complex than this.) A blue-eyed man marries a brown-eyed woman, and they have six children, all brown-eyed. What is the most likely genotype of the father? What is the most likely genotype of the mother? If the seventh child had blue eyes, what can you conclude about the parentsʹ genotypes? Answer: The most likely genotype of the father is bb (homozygous recessive) for the trait. The most likely genotype for the mother is either Bb (heterozygous with both a dominant and a recessive gene) or BB (homozygous dominant) for the trait. If the seventh child had blue eyes, the motherʹs genotype would be Bb, and the fatherʹs genotype still would be bb. 72 8) Suppose an XcXc female marries an XcY man. (a) What is the probability of producing a color-blind son? (b) What is the probability of producing a color-blind daughter?

(c) What is the probability of producing a daughter who is a carrier for the color-blind gene? (d) What is the probability of having four sons in a row? Answer: (a) 100% of their sons will be color-blind. (b) 100% of the daughters will be color-blind. (c) None of the daughters will be carriers for the color-blind gene. (d) The probability of having four sons in a row is 1/16, or slightly better than 6%. 73 9) Assume that brown eyes (B) are dominant over blue (b); and right-handedness (R) is dominant over left-handedness (r). A brown-eyed, right-handed man marries a blue-eyed, right-handed woman. Their first child is brown-eyed and right-handed, and their second child is blue-eyed and left-handed. What are the genotypes of the parents? Answer: The man has a BbRr genotype, while the woman has a bbRr genotype. 74 10) This is a first pregnancy for a 22-year-old woman. She is in her 16th week of pregnancy.

She is scheduled for an amniocentesis and expresses concern that the ʺbaby will be stuck with the needle.ʺ What should the nurse say to the client? Answer: The nurse should explain that this is a fairly simple procedure and that an ultrasound will be used to visualize the position of the fetus and the amniotic sac. 75 11) A client is heterozygous for sickle-cell anemia. Explain why the client would have few or no symptoms of sickle-cell anemia. Answer: Individuals heterozygous for the sickling gene make both normal and sickling hemoglobin. As a rule these individuals are quite healthy, but they can suffer if there is prolonged reduction in blood oxygen levels. 76 12) A nurse is providing genetic counseling to a couple who both have the sickle-cell anemia trait, but not the disease. The couple is trying to decide whether or not to have a child. What is the possibility a child would inherit the disease? What is one reason they might consider not having a child? Answer: The chances of having a child with the disease are 25%.

A reason not to have a child is that if a child is afflicted with sickle-cell anemia, the child will suffer and have severe pain. 1) When two genes are on the same chromosome, they are considered linked. Answer: TRUE 2) The X chromosome is considerably larger than the Y chromosome. Answer: TRUE 3) Incomplete dominance is more uncommon in humans. Answer: TRUE 4) Some segments of the Y chromosome have no counterpart on the X chromosome. Answer: TRUE 5) Chromosomes that are not directly involved with sex determination are called sex-linked. Answer: FALSE 6) Hereditary characteristics are transmitted to offspring by genes. Answer: TRUE 7) Alleles may code for alternative expressions of a genetic trait. Answer: TRUE 8) Hemophilia is an X-linked condition caused by a recessive gene. Answer: TRUE The Genetic Testing Controversy The Genetic Testing Controversy Tim Friesen Copyright 1997 Genetic screening uses a variety of laboratory procedures to find out if a person has a genetic condition or disorder or is likely to develop a disease based on his or her genetic makeup.

Individuals may wish to be tested if the family shows a history of one specific disease such as Huntington's Disease or breast cancer, if they show symptoms of a genetic disorder which could be improved by early diagnosis, or if they are planning a family and are concerned about the possibility of passing on a genetic trait to their offspring. This last type of screening can look at the parent's genotype or look at the genotype of the fetus or newborn. This type of screening can also look for a specific disorder or can be done as a general test for common disorders as in prenatal testing or more commonly newborn screening. Genetic tests use techniques to examine genes or markers near the genes. Direct testing for diseases such as Cystic Fibrosis and Sickle Cell Anemia come from an analysis of an individual's specific genes. A technique called linkage analysis, or indirect testing, is used when the gene cannot be directly identified but can be located within a specific region of a chromosome. This testing requires additional DNA from an affected family member for comparison. Because each person's DNA is unique (except for identical twins), genetic tests also can be used for individual identification ("DNA fingerprinting").

This technique is often used in forensic work, where samples from a crime scene such as blood or semen could be used as incriminating or acquitting evidence. Genetic testing is a complex process, and the results depend both on reliable laboratory procedures and an accurate translation of results. Tests also vary in sensitivity, that is, their ability to detect mutations or to detect all patients who have or will develop the disease. Interpretation of test results are often complex even for trained physicians and other health care specialists. Types of Genetic Testing Carrier Identification includes genetic tests used by couples whose families have a history of recessive genetic disorders and who are considering having children. Three common tests include those for cystic fibrosis, Tay-Sachs disease, and sickle-cell trait but more tests are coming on the market at a very high rate. Norman Frost of the University of Wisconsin Madison Medical School says, "Potential new genetic tests roll off the conveyor belt of the human genome project almost once a week " (2). Preimplantation Genetic Diagnosis (PGD) combines recent advances in genetics with the well established techniques of in vitro fertilization (IVF). In IVF, a woman's monthly reproductive cycle is manipulated.

She is given hormones that stimulate her ovaries so that many eggs mature at one time. The eggs are surgically collected and fertilized with her partner's sperm in a lab dish. The resulting embryos are then transferred to the women's uterus and, if all goes well, pregnancy begins (3). In 1989, a couple by the names of Renee and David Abshile, who were both carriers of the disabling condition Tay-Sachs, lost a daughter to the lethal disease. Because Tay-Sachs is a recessive disorder, two carrier parents each have a 50% chance of donating an abnormal allele. This gives the newborn a 25% chance of procuring both recessive abnormal alleles, a very high risk when regarding humans. According to a Scientific American report (2), the Abshiles promised they would never again have another child unless they could be sure it would not be predisposed to the disorder. The only way to be sure was to have a prenatal genetic test that would show whether or not the child would acquire the disorder based on its genetic makeup. This type of test has its obstacles in that if the fetus does have the abnormal genetic makeup, the only way to stop it is to abort the fetus.

Abortion was not an option for the Abshiles because of strong religious beliefs. The Abshiles were out of luck until they heard of a new procedure of genetic testing called preimplantation genetic diagnosis (PGD) in which fertilization is done in vitro (IVF) and the cells are grown to a multicell stage and then tested for the genetic mutation/malfunction. In the Abshile's case, they were able to implant three pre-embryos that were not even carriers for the disease. From those three embryos came the first baby to be certified free of the Tay-Sachs disease. Prenatal Diagnosis is genetic testing of a fetus. This may occur when there is a risk of bearing a child with genes associated with mental retardation or physical deterioration. Down Syndrome is one of the most common genetic diseases screened by this method. Prenatal testing is probably the most controversial type of diagnosis because of the abortion issue. When do we draw the line on abnormalities? Is it ethical for parents to abort a child because the child will have Tay-Sachs disease or an even more ethically consuming question, is abortion okay if the child is not going to be the right sex?

According to the book Feminism and Bioethics: Beyond Reproduction, Korea is currently predicting a 10% increase in the male to female ratio within the next thirty years. Sex selection is illegal in Korea but doctors give unspoken results through the amount of enthusiasm they show the mothers. If the doctor lacks enthusiasm upon the test results, the mother often calls for an abortion, knowing that the fetus is a female (1) Newborn Screening is frequently done as a preventative health measure. Tests usually have clear benefit to the newborn because treatment is available. Phenylketonuria and congenital hypo-thyroidism are conditions for which newborn testing is conducted in all 50 states. Late-onset Disorders include adult diseases such as Huntington's Disease, cancer and heart disease. Diseases like cancer and heart disease are complex and have both genetic and environmental causes. Genetic tests may indicate a susceptibility or predisposition for these diseases. Diseases like Huntington's disease, are caused by single genes that also are seen later in life. These types of disorders can be tested for at any time. Recently through studying blood samples of families in which there is a history of breast cancer, scientists have isolated and identified a gene linked to breast cancer.

In families with hereditary breast cancer, which accounts for less than ten percent of all cases, mutations in the BRCA1 gene confer an 85% lifetime risk of the disease, as well as a 45% chance of ovarian cancer. Some women in such families who have learned that they carry a mutated BRCA1 have elected to undergo Prophylactic mastectomy and oophorectomy (removal of the ovaries), a procedure that may reduce but does not eliminate the risk of cancer (4). By being able to identify these genes through particular "markers" associated with the gene, doctors will know which individuals are more susceptible to cancer and therefore can follow the proper procedures to more effectively observe the individuals for signs of the disease. The earlier the doctor can diagnose the cancer the more effective the treatment will be. Mass population testing is a large scale testing usually of a particular ethnic group that shows a high rate of a specific genetic disorder. This type of testing has been both successful and unsuccessful. A voluntary genetic screening program was set up in the early 1970's for Tay-Sachs disease. It has been a huge success.

More than a million Jews throughout the world, which Tay-Sachs predominantly affects, have volunteered to be tested to see if they were carriers of this genetic disorder. A carrier is not affected because to develop the disease symptoms, a person must carry two recessive alleles, one from each parent. Before the people were tested they were educated as to what the tests would mean and what they could do with the information from the tests. Once they were tested, genetic counseling was available to answer any questions about the implications of the tests. This mass genetic test was a huge success, especially to Jews because it gives the individual the knowledge they needed to plan their family future. About the same time as the Tay-Sachs testing was taking place, another ethnic minority group was being tested. This testing was for a different disorder with a very different response. African Americans were being tested for the blood disorder sickle cell anemia. This mass testing was not as big a success as the Tay-Sacks testing for a number of reasons. The disease sickle cell anemia is a hereditary disease that affects the hemoglobin molecule. The result is a sickle shaped red blood cell which, in the absence of oxygen, clumps.

The two alleles for sickle cell are codominant and a heterozygous individual (Ss) produces both normal and sickle shaped blood cells. People homozygous for the sickle cell allele rarely make it to reproduce. The screening was done by an easy-to-administer blood test that could be given by anyone, including clergymen and local community volunteers. The test checks for carriers who will have some sickle cell RBC and some normal. Where the test was faulty was the lack of education that went along with the tests. Massachusetts required African American children at risk for sickle cell to be tested before entering school and soon the people carrying a single allele were thought to be diseased even though there were no outward manifestations of the disorder. To add fuel to the fire, scientists suggested that the solution was for blacks carrying the allele to forego breeding. This sent a message that the screening was a eugenics attempt by the federal government (who funded the program) to eliminate the African American community (2). Even though this mass testing started out with the best of intentions for the African American community, it ended in disaster because of poor planning.

Because of the implications that could and do arise from mass genetic testing, it is a volatile issue and needs to be approached most delicately and tactfully. Individual Identification can be used in areas ranging as widely as forensic testing to paternity testing. In these cases a "DNA fingerprint" is used to compare two different individuals or samples to see how closely they match. The O.J. Simpson trial is a well known example of individual identification where a blood sample was found and matched to the accused. It is also possible to do individual identification testing in a prenatal fashion as will be described in the following scenario provided by the U.C. Berkeley program in Genetic Counseling and Georgetown University Medical Center. The scenario is based on an actual situation. Mr. and Mrs. C. come to a genetics clinic for prenatal diagnosis. Both are carriers of one cystic fibrosis allele. Cystic fibrosis is a lung disorder which causes a mucous buildup and prevents proper breathing. Mrs. C, who is pregnant, undergoes the prenatal test. The results that come back show the fetus having two abnormal cystic fibrosis alleles, but with a small twist of gargantuan proportions.

Much to the dismay of the doctor, one of the mutations that the baby carries is different from that of the mother or the father, making it virtually certain that Mr. C is not the father. This scenario shows both an example of prenatal testing, but more importantly, individual identification. Conclusion on genetic testing Genetic testing is not a single technology. Rather, it refers to a broad range of methods for gauging the presence, absence or activity of genes in cells. At the relatively low tech end, researchers can count the chromosomes in a patient's cells or measure the amount of tell tale proteins in his or her blood. At the most sophisticated level, researchers assay a cell's DNA with molecular probes that can find a specific genetic sequence among the three billion base pairs that make up human DNA. (2) Genetic testing can cost less than $50 for a simple blood screening for sickle cell or cost in the $10,000 range for a complicated preimplantation genetic test for Tay Sachs disease. These are two extremes of genetic tests with varying costs. Real and conceivable controversies Genetic screening has great potential for our society. It has the capability of improving and lengthening human life.

If used in an ethical manner, genetic testing can eliminate unforseen suffering and distress. But, issues such as privacy, consent, discrimination, equity, and social engineering are potential barriers that many individuals have confronted already. Both legal and personal family conflicts may arise because of testing of individuals or immediate relatives. Privacy What about privacy? Does it really exist? Should it exist? How can we ensure that it does? These questions and more are being studied by researchers in order to make genetic screening as promising a technology for improving human health and longevity as possible. The Alliance of Genetic Support Groups, in Chevy Chase, MD says that, "information learned about you or your family through your participation in genetic research can become known to persons other than the research team." (5) This is incriminating evidence for the lack of genetic privacy. Should others have access to your genetic records? According to a nationwide Time/CNN poll, 90% of respondents thought it should be illegal for insurance companies to use genetic tests to decide whom to insure.

But regardless of public opinion, a 1992 congressional study revealed that underwriters at 11 of 25 Blue Cross/Blue Shield plans said they would turn down an applicant if pre-symptomatic testing discovered likelihood of a disease. (6) Genetic Privacy can also bring up other issues like who has the right to know? Because your genes are not exclusively our own (you share your genes with your parents and siblings), do you have a moral obligation to tell potentially affected individuals. Is it important whether the effect is direct or indirect? A 1992 March of Dimes poll showed that 98% of those polled thought a spouse or betrothed should know about a defective gene(4). If for instance you find through genetic testing that you are carrying two BRCA1 dysfunctional alleles for breast cancer, this means your mother also carries the gene and is at risk. If you carry two alleles your female siblings also are at a potential risk. What if you don't tell anyone? Does your doctor have the ethical obligation to tell your family members that could be affected? Should this be a legal obligation?

In a poll of doctors, 54% said that even over a patient's objections, they would tell relatives at risk about the results of a test from Huntington's Disease. 24% said they would tell a patient's employer and 12% said they would tell an insurance company (4). This makes the privacy issue a bit more perplexing. Consent Do individuals have the right not to know? This has been a question that the Federal government has been toying with, but so far has left up to individual states to regulate. Many states have proposed legislation similar to the one proposed by Indiana in 1997. This legislation would prohibit insurance companies from forcing people to be tested in order to be insured and would also prohibit inquiries into the results regarding genetic screening or testing (9). But is it possible to stop all inquiries into genetic testing? Insurance companies have the right to look at medical records and family histories before granting coverage and indirect or direct genetic results could be obtained from these records. Unfortunately, these are all questions that will inevitably be answered in our court systems. Discrimination Discrimination could be a nightmare to someone with a genetic disorder or to someone with a family history of genetic disorders.

A study done at Georgetown University looked at the perceptions of 332 members of genetic support groups and found that 25% of respondents of affected family members believed they were refused life insurance. 22% believed they were refused health insurance and 13% believed they were denied or let go from a job due to a disclosure of confidential genetics testing results (7). Many doctors have indicated that people will get genetic testing done anonymously or under false names in order to avoid potentially discriminating situations (4). Even if a genetic test is not done, discrimination based on possible gene makeup can still take place. One woman who applied to become an adoptive parent was denied because a family history of Huntington's disease made her a high risk (2). In another case, a family's HMO learned of a prenatal genetic test showing that the fetus carried two recessive alleles for Cystic Fibrosis. When the HMO learned that they were going to continue with the pregnancy the family was informed that if the pregnancy was not terminated, movement to withdraw or limit the entire family's health coverage would result. This was the case until threats of lawsuits from the family encouraged the HMO to change their minds (2). Equity Is genetic testing equally available to all?

Will the rich be able to alienate itself from all genetic problems creating a lower class of outcasts? Before the start of the Human Genome Project, genetic abnormalities spanned all socioeconomic classes with similar percentages. This is no longer the case. If gene patenting is allowed to proceed, the cost of genetic tests could skyrocket based on demand. This could lead to only the wealthy being able to afford genetic testing and from this, genetic problems could be isolated to the poor. Social Engineering Leon Kass makes excellent sense in the following statement, "I was conceived after antibiotics yet before amniocentesis, late enough to have benefitted from medicine's ability to prevent and control fatal infectious diseases, yet early enough to have escaped from medicine's ability to prevent me from living to suffer from genetic diseases.

To be sure, my genetic vices are, as far as I know them, rather modest, taken individually -myopia, asthma and other allergies, bilateral forefoot adduction, bowleggedness and pessimism, plus some four to eight as yet undiagnosed recessive lethal genes in the heterozygous condition-but taken together, if diagnosable prenatally, I might never have made it." (10) But is preimplantation testing, that looks for desirable traits, all bad? Is it wrong for a parent to desire to choose the best traits in its soon-to-be offspring? Some critics say it would give the parents a more enthusiastic role in conceiving a child if they had some control over its beginnings. Are we out to make the perfect child? It may seem farfetched now, but what if we could? Will we ever have the technology to make a human more intelligent ? This may only be a pipedream.

As geneticist Eric Lander puts it, "We can tinker at the edges, but we are talking about an understanding of single components in a system that has 100,000 components." As long as that's the case, the best way to produce smarter kids is to educate them (11). But, when it comes to humans, who knows what we will try to do. Conclusion All of this discussion and debate ultimately stems from the Human Genome Project. This project is an international effort to map and sequence all the genes of the human cell. The project has allocated a large amount of its funds, some $40 million, to the ethical, legal and social implications (ELSI) of genetic research. This allocation has created many social, legal, and hard science studies. These studies included the production of a widely accepted set of principles to guard against genetic discrimination, insuring quality in DNA labs, educating doctors in the use of genetic data, and guiding researchers on obtaining informed consent. Many of the issues that are controversial with the system revolving around genetic testing can be prevented with foresighted social and legal policies, health care reform, and state and national legislation.

But European countries with universal health care and national legislation still have problems with discrimination and privacy. Do we eliminate the most extensive technology ever known to man or do we do our best to improve on the mistakes we have made and create a better world for the future? In order to improve on anything, a risk must be taken. It would be cowardly to obliterate the potential good from this endeavor. With this in mind, I am reminded of my favorite quote by probably the most famous scientist of all time, Albert Einstein. "Great spirits have always encountered violent opposition from mediocre minds" As a conclusion I can not say it any better than Tom Dworetzky (8). "I'm not saying we shouldn't proceed with the Human Genome Project. The gifts it will bear in treatment for devastating inherited diseases outweigh its societal risks. However, we must begin, individually and collectively, to prepare for this knowledge by addressing our prejudices. Those are the most deadly of all inherited diseases, ones we must cure before our genetic knowledge will ever flower into wisdom and we truly become human beings." References 1. Wolf, Susan M. Feminism and Bioethics: Beyond Reproduction, Oxford University Press. New York 1996. 2. Rennie, John.

Trends in Genetics: Grading the Gene Tests. Scientific American. June 1994 pp. 88-97. 3. Grady, Denise. Unnatural Selection. Vogue. Oct 1995. pp. 230-236. 4. Beardsley, Tim. Trends in Human Genetics: Vital Data. Scientific American. March 1996 pp. 100-105. 5. Genetic Tests and Descrimination 97/spr9709.html last accessed 10-31-97 6. Genes on the Line last accessed 11-1-97 7. Lapham, E. Virginia; Kozma, Chahila; Weiss, Joan O. Genetic Discrimination: Perspectives of Consumers Science. Vol 274. 24, Oct 1996. pp. 621-624. 8. Dworetzky, Tom No Deltas Need Apply: Will DNA Mutation F508 make you an outcast? Omni, v 15, n 5, Feb-Mar 1993. p.

16. 9. Digest of introduced bill affecting Indiana code 27-4-1-4 ; 27-8-25. effective July 1, 1997 10. The Ethics of Genetic Testing last accessed 11-1-97 11. Cowley, Geoffrey. The View from the Womb, Genetics: Babies to Order Remain a Pipedream. Newsweek. 8 November 1993. p.64. 12. Marshal, Eliot. The Genome Programs Conscience, Science. v 274. 25, October 1996 pp. 488-90. Test Crosses | Learn Science at Scitable Aa Aa Aa It is not always possible to determine what genes an organism is carrying by simply looking at its appearance. After all, gene expression is a complex process that is dependant on many environmental and hereditary factors. For example, Gregor Mendel's experiments with pea plants showed how dominant traits can mask recessive ones, thus causing him to muse how "rash it must be...

to draw from the external resemblances of hybrids conclusions as to their internal nature" (Mendel, 1866). Today, scientists use the word "phenotype" to refer to what Mendel termed "external resemblance" and the word "genotype" to refer to an organism's "internal nature." Thus, to restate Mendel's musing in modern terms, we cannot infer an organism's genotype by simply observing its phenotype. Indeed, Mendel showed that phenotypic traits can be hidden in one generation, yet reemerge in subsequent generations. This occurs because some alleles are dominant over others, which means that their phenotype will mask the phenotype associated with the recessive alleles. Because of dominance, there is not a one-to-one correspondence between the alleles that an organism possesses (i.e., its genotype) and the organism's observed phenotype. Consider, for instance, the genes that code for eye and body color in the fruit fly Drosophila melanogaster. In these flies, the brown-eye allele (b) is recessive to the normal red-eye allele (B). Similarly, the ebony body color allele (e) is recessive to the normal (yellow-brown) body color allele (E).

Because ebony has 100% penetrance , a fly that has dark black body color has the homozygous genotype ee. However, a fly that has a normal body color may have the homozygous genotype EE or the heterozygous genotype Ee. Things get slightly more complex when considering two genes. For instance, a wild-type fly (with red eyes and a yellow body) has one of four possible genotypes: EEBB, EEBb, EeBB, and EeBb. There is no way to tell these genotypes apart visually, but there is a well-established experimental technique to determine the fly's genetic makeup. Specifically, to detect the underlying genotype of an organism with a dominant phenotype, one must do a type of breeding analysis called a test cross. The test cross is another fundamental tool devised by Gregor Mendel. In its simplest form, a test cross is an experimental cross of an individual organism of dominant phenotype but unknown genotype and an organism with a homozygous recessive genotype (and phenotype). In order to understand how test crosses work, it helps to consider several examples, including those that involve just one gene of interest, as well as those that involve multiple genes.

Single-Gene Test Crosses Recall that in the fruit fly Drosophila melanogaster, the ebony-body allele (e) is recessive to the normal yellow-body allele (E). Say you are given a male fly with a yellow body. How could you use a test cross to determine this fly's genotype? In order to set up your test cross, you must first realize that the male fly has one of two possible genotypes: Ee or EE. Because the male exhibits the dominant body color phenotype, you must cross it with a female with the homozygous recessive phenotype and genotype. Thus, the male fly is crossed with an ebony-bodied female of genotype ee. Depending on the male fly's underlying genotype, this cross will yield one of two possible sets of outcomes, as depicted in Tables 1 and 2. Table 1: Outcome if Male Fly Is Heterozygous (Ee)

Question: What name is given to the genetic make-up of an individual?
Answer: Genotype