answer this qcm about genetics correctly:     170. A DNA strand has the following characteristics :
        1. The nitrogenous bases of DNA are adenine, cytosine, uracil and thymine
        2. The nitrogenous bases of a strand are strictly codetermined
        3. The "reading" direction of the genetic information is determined by the 5' - 3' polarity of the DNA strand
        4. The presence of a nitrogenous base in one nucleotide does not exclude the presence of any of the four nitrogenous bases in the two neighbouring nucleotides
        5. The phospho-glucid skeleton is the constant part
        6. It has a free -OH group at the 3' end and a free -PO4 group at the 5' end
        7. It is linear
        8. The genetic information encoded on the DNA strand, which determines the order of amino acids in proteins, can be read either way
        9. Nitrogenous bases bind laterally, perpendicular to the phospho-glucid axis through bonds between an N atom of the nitrogenous base and the orthophosphoric acid
        10. The 5'-ACGTCAG-3' strand corresponds on the complementary strand to the sequence 5'-TGCAGTC-3'.
    171. Which of the following statements is true about the secondary structure of DNA?
        1. Phospho-diester bonds are made between the nitrogenous bases of the two strands of the same DNA molecule
        2. The two strands are wrapped plectonemically, one around the other and both around a central axis
        3. The presence of a nitrogenous base on one strand does not require the presence of a certain complementary base on the other strand
        4. The two strands are attached to each other by hydrogen bridges, formed between the complementary nitrogen bases
        5. The sum of purine bases is different from the sum of pyrimidine bases
        6. Adenine binds to thymine via two hydrogen bonds and cytosine to guanine via three bonds
        7. In the large groove of the DNA molecule histones bind
        8. Both strands in the DNA molecule are 5'→3' polarized and run in parallel
        9. The two strands are antiparallel, they have reverse polarization to each other
        10. The two strands are complementary and co-determined
    172. The nucleus has the following features:
        1. Sex cells have 23 chromosomes, representing a diploid set of chromosomes
        2. The genetic information in the nucleus of somatic cells represents the genotype
        3. The genetic information in the gamete nucleus is the genome
        4. The nucleus of mature sex cells contains 23 chromosomes
        5. The number of chromosomes in the nucleus is not a species characteristic
        6. The nucleus of somatic cells contains 46 chromosomes, grouped into 23 pairs
        7. The nucleus contains chromatin fibres and chromosomes, between which there are chemical structural differences
        8. The nucleus contains DNA molecules visible under the electron microscope as chromatin fibres during division and as chromosomes in the interphase
        9. The nucleus contains 99.5% of the cell's DNA
        10. The nucleus contains chromatin fibres, the structure of which is visible under the light microscope
    173. Chromatin has the following features:
        1. Represents the way genetic material is organized in the interphase
        2. It consists of RNA, histone proteins, non-histone proteins and bivalent ions
        3. Constitutive heterochromatin is found at the centromeres and telomeres of all chromosomes
        4. Can be identified under the light microscope as fine, weakly stained granules - euchromatin - or strongly stained granules - heterochromatin
        5. Eucromatin is only visible during prophase, because during interphase it is genetically active
        6. Euchromatin is poorly stained, poorly condensed and contains a large amount of repetitive DNA and non-histone proteins
        7. Heterochromatin and euchromatin are morphologically, biochemically and functionally identical
        8. Constitutive heterochromatin is present in some individuals and constitutes sex chromatin
        9. Eucromatin is poorly condensed and is the genetically active part of chromatin
        10. Heterochromatin is highly condensed, contains repetitive DNA and represents the genetically inactive zones of chromatin fibres
    174. Sex chromatin X:
        1. Occurs through early inactivation immediately after birth
        2. Reflects the inactivation of one of the two X chromosomes in the female
        3. The X chromosome that inactivates is the X chromosome of paternal origin
        4. Chromatin X may be seen in men with Klinefelter syndrome
        5. Can be seen in the nucleus of all cells of a female person and, in pathological conditions, in some males
        6. Occurs by random inactivation of an X chromosome, only in some tissues
        7. In cells with unbalanced X chromosome abnormalities, the normal X chromosome is preferentially inactivated
        8. Mary Lyon's hypothesis is not completely valid, as some genes escape inactivation
        9. Sex chromatin X can normally be identified in the nucleus of cells from both sexes
        10. The condensing of X chromatin is based on differences in gene content between the X and Y chromosomes
    175. The Barr body represents:
        1. In pathological conditions it is absent in women and may be present in men
        2. It is usually found in 20-40% of cells tested from a normal female
        3. It is represented by any corpuscle of heterochromatin visible inside the nucleus
        4. Chromatin X identified in the nucleus of oral mucosa cells
        5. Under normal conditions a woman has 2 Barr bodies, because she has two X chromosomes
        6. Allows identification of the number of X chromosomes in the nucleus of the cells concerned, and thus can be useful in determining genetic sex
        7. An intensely stained heterochromatin corpuscle located on the inner face of the nuclear membrane
        8. It is less than 1 micrometer in the case of the long-arm X isochromosome
        9. Does not vary in size according to X chromosome structure
        10. Can never be identified in a male
    176. The advantages and practical indications of the Barr test are:
        1. It is a quick, inexpensive test and requires minimal laboratory equipment
        2. Detection of monosomy X and diagnosis of Turner syndrome in females with short stature and primary amenorrhea
        3. Does not allow the identification of gonosomal tetra- and pentasomies
        4. Not indicated in girls with secondary amenorrhea
        5. Allows the identification of XXY gonosomal trisomy and the diagnosis of Klinefelter syndrome in men with high waist, small testicles and gynecomastia
        6. Allows the genetic sex of newborns with intersex conditions to be determined and the genetic and civil sex to be matched
        7. Does not allow identification of X-chromosome aneuploidy
        8. Does not allow genetic sex identification of tissue fragments
        9. Not useful in autosomal chromosomal diseases
        10. It is a screening test in Down syndrome
    177. Chromatin Y represents:
        1. It is not a form of sex chromatin because it cannot be found in female organisms
        2. Cannot be evident in any nucleated cell type
        3. Does not allow for genetic sexing of tissue fragments in forensic medicine
        4. Interphase aspect of heterochromatin on the long arm of the Y chromosome
        5. In individuals with abnormal chromosome formulae such as 48,XXXY or 49,XXXXY, the F body is not identified
        6. Can be detected in cells harvested from males by fluorochrome staining and examination under ultraviolet light
        7. In females, regardless of the number of X chromosomes, there is no F body
        8. In individuals with chromosome formula 47,XYY there are two F bodies
        9. It is also called F body, the number of bodies identified being equal to the number of Y chromosomes existing in the cells analysed.
        10. Examined under the ordinary light microscope
    178. About the DNA structure it is known that:
        1. The links between the two strands are unstable and can break spontaneously
        2. At the level of the double spiral there are two grooves (incisions)
        3. No functional differences between the two outer grooves of the DNA molecule
        4. The links between the two strands are made by the random pairing of nitrogenous bases
        5. Cytosine and guanine are complementary
        6. The diameter of the DNA molecule is 20 Å (20 x 10-10 m)
        7. Enzymatic cleavage of hydrogen bridges is involved in chromosome formation
        8. Hydrogen bonds can break and then spontaneously rebuild, a process called renaturation
        9. The polarity of DNA strands changes at different times in cellular life
        10. The two strands of DNA - are plectonemically wound
    179. About chromatin and sex chromatin it can be stated that:
        1. Heterochromatin is rich in AT pairs and represents the genetically inactive zones of chromatin fibres
        2. The number of Barr bodies equals the number of X chromosomes + 1
        3. Chromatin is the way genetic material is organised in prophase
        4. Eucromatin is rich in CG base pairs and replicates early during S phase
        5. Chromatin is made up of DNA associated with histones, small amounts of RNA and non-histone proteins
        6. X chromosome inactivation is a random process in women
        7. Xist (X Inactive Specific Transcript) gene ensures the synthesis of mRNA molecules that ensure the complete functioning of genes on the 2 X chromosomes in females
        8. Eucromatin forms the centromere and telomeres
        9. One of Mary Lyon's hypotheses is that inactivation of an X chromosome in women is early and definitive
        10. In the case of X chromosome inactivation, inactivation was found to be complete, with all genes on the chromosome inactivated
    180. About repetitive sequences it can be stated that:
        1. They can form "families" of related sequences, some with known function, that represent the genetic fingerprint of each individual
        2. Repetitive sequences may be highly or moderately repetitive
        3. Simple repetitive sequences enter into the composition of euchromatin
        4. Hypervariable minisatellites (VNTR - variable number of tandem repeats) are individual genetic markers that can be used to identify individuals
        5. Tandem repetitive sequences are rare and found only in acrocentric chromosome satellites
        6. Simple repetitive sequences are transcribed into RNA molecules of known function
        7. Repetitive sequences occur in regions of heterochromatin
        8. Repetitive sequences are rare in the human genome
        9. Microsatellites (VNDR - variable number of dinucleotide repeats) are the shortest repetitive sequences
        10. Pseudogenes are non-functional copies of genes
    181. About the secondary structure of DNA it is known that:
        1. DNA shows a dextrorotatory spiral (coiled right to left)
        2. The complementary pairs that form are of the purine-purine or pyrimidine-pyrimidine type
        3. Adenine and thymine are complementary
        4. In the large groove of the DNA molecule histones bind
        5. The small groove binds transcription and translation factors
        6. Hydrogen bonds can be broken experimentally by heating or by the action of bases or acids, a process called denaturation
        7. DNA has a variable diameter, depending on the complementary nucleotides
        8. The two phospho-glucidic axes are located on the outside, while the nitrogenous bases attached by hydrogen bridges are located in the middle
        9. The chain 5-ATCGTTAACG-3' corresponds to the complementary chain sequence 3'-TAGCAATTGC-5'
        10. The nucleotides of a strand are linked by bonds between the -PO4 group on carbon 3 (3' position) of a nucleotide and the -OH group on thecarbon 5 (5' position) of the other nucleotide
    182. The supramolecular organization of chromatin implies that:
        1. The number of loop attachment points on the protein scaffold is low in heterochromatin regions
        2. Nucleosome forms chromosomal domains with functional autonomy (replication and transcription)
        3. Chromatid condensation continues during cell division, reaching its maximum degree of condensation in metaphase, when it is 700 nm
        4. The solenoid has a homogeneous structure because the spiral zones depend on complementary base-pairing
        5. The nucleosome is made up of 8 histone molecules around which a DNA fragment coils
        6. Folding the solenoid into side loops on a backbone of non-histone acidic proteins will provide 10-fold DNA compaction
        7. By spiralization and condensation of the folded chromatin fiber into side loops, chromosome chromatids will form at the beginning of prophase
        8. Spiralization and condensation of chromatin fibers is fixed and cannot change during the cell cycle
        9. The core of the nucleosome consists of histone H1 class proteins
        10. Spiralization of the nucleosomal fibre forms the solenoid, providing 5-fold compaction
    183. Human chromosomes:
        1. They have three obligatory morphological elements: centromere, telomeres and chromatids
        2. They can be classified as metacentric, submetacentric and acrocentric according to the position of the centromere
        3. Chromosome morphology is easy to analyze in metaphase
        4. Telomeres are structures by which the chromosome attaches to the division spindle
        5. Ensures the transmission of genetic information in the succession of generations of cells and organisms
        6. Acrocentric chromosomes have the centromere located in the intermediate position
        7. The chromatids of a chromosome are called sister chromatids
        8. Have secondary constriction evidenced as a thickening in the centromere area
        9. Autosomes in a somatic cell constitute 23 pairs
        10. Gonosomes are the chromosomes of sex cells
    184. Telomeres have the following features:
        1. Telomere shortening is a phenomenon that prolongs the lifespan of a cell
        2. Involved in aging and cancer
        3. Telomeres are absent in acrocentric chromosomes
        4. They are the terminal parts of chromatids
        5. Telomere replication is provided by a ribonucleoprotease, called telomerase
        6. Multiple copies of genes encoding ribosomal RNA are located at telomeres
        7. Maintain chromosome integrity
        8. Telomerase is active in most somatic cells throughout life
        9. FISH telomere probes attach to the short arms of chromosomes
        10. Formed of repetitive DNA
    185. Chromosomes have particular morphological elements about which it can be said:
        1. The Y chromosome frequently has satellites
        2. Satellites are masses of heterochromatin attached to the short arms of acrocentric chromosomes
        3. Secondary constrictions are only present on sex chromosomes
        4. Genes encoding ribosomal RNA are located on group E chromosomes
        5. Presence of giant satellites is common in Down syndrome
        6. FRAXA fragile site is associated with Klinefelter syndrome
        7. Satellites may be present in the extension of the short arms of chromosomes 13, 14, 15
        8. Secondary constrictions are located pericentromeric, on the long arm of some chromosomes
        9. Fragile sites are decondensed chromosomal regions due to the presence of an abnormal gene
        10. The pericentromeric, less stained areas on the long arms of chromosomes 1, 9, 16 are called secondary constrictions