The person who first did twin studies was Francis Galton, Darwin's half-cousin, who was a founder of statistics. His method was to trace twins through their life-history, making many kinds of measurement. Unfortunately, though he knew about mono and dizygotic twins, he did not appreciate the real genetic difference. Twin studies of the modern kind did not appear until the 1920s.
The genetics of bacteria, archaea and viruses is a major field of research. Bacteria mostly divide by asexual cell division, but do have a kind of sex by horizontal gene transfer. Bacterial conjugation, transduction and transformation are their methods. In addition, the complete DNA sequence of many bacteria, archaea and viruses is now known.
Although many bacteria were given generic and specific names, like "Staphylococcus aureus", the whole idea of a species is rather meaningless for an organism which does not have sexes and crossing-over of chromosomes. Instead, these organisms have strains, and that is how they are identified in the laboratory.
Gene expression is the process by which the heritable information in a gene, the sequence of DNA base pairs, is made into a functional gene product, such as protein or RNA. The basic idea is that DNA is transcribed into RNA, which is then translated into proteins. Proteins make many of the structures and all the enzymes in a cell or organism.
Several steps in the gene expression process may be modulated (tuned). This includes both the transcription and translation stages, and the final folded state of a protein. Gene regulation switches genes on and off, and so controls cell differentiation, and morphogenesis. Gene regulation may also serve as a basis for evolutionary change: control of the timing, location, and amount of gene expression can have a profound effect on the development of the organism. The expression of a gene may vary a lot in different tissues. This is called pleiotropism, a widespread phenomenon in genetics.
Alternative splicing is a modern discovery of great importance. It is a process where "from a single gene a large number of variant proteins can be assembled". One particular Drosophila gene (DSCAM) can be alternatively spliced into 38,000 different mRNA.
Epigenetics is the study of changes in gene activity which are "not" caused by changes in the DNA sequence. It is the study of gene expression, the way genes bring about their phenotypic effects.
These changes in gene activity may stay for the remainder of the cell's life and may also last for many generations of cells, through cell divisions. However, there is no change in the underlying DNA sequence of the organism. Instead, non-hereditary factors cause the organism's genes to behave (express themselves) differently.
Hox genes are a complex of genes whose proteins bind to the regulatory regions of target genes. The target genes then activate or repress cell processes to direct the final development of the organism.
There are some kinds of heredity which happen outside the cell nucleus. Normal inheritance is from both parents via the chromosomes in the nucleus of a fertilised egg cell. There are some kinds of inheritance other than this.
Mitochondria and chloroplasts carry some DNA of their own. Their make-up is decided by genes in the chromosomes and genes in the organelle. Carl Correns discovered an example in 1908. The four o'clock plant, "Mirabilis jalapa", has leaves which may be white, green or variegated. Correns discovered the pollen had no influence on this inheritance. The colour is decided by genes in the chloroplasts.
This is caused by a symbiotic or parasitic relationship with a microorganism.
In this case nuclear genes in the female gamete are transcribed. The products accumulate in the egg cytoplasm, and have an effect on the early development of the fertilised egg. The coiling of a snail, "Limnaea peregra", is determined like this. Right-handed shells are genotypes "Dd" or "dd", while left-handed shells are "dd".
The most important example of maternal effect is in "Drosophila melanogaster". The protein product maternal-effect genes activate other genes, which in turn activate still more genes. This work won the Nobel Prize in Physiology or Medicine for 1995.
Much modern research uses a mixture of genetics, cell biology and molecular biology. Topics which have been the subject of Nobel Prizes in either chemistry or physiology include:
Many well-known disorders of human behaviour have a genetic component. This means that their inheritance partly causes the behaviour, or makes it more likely the problem would occur. Examples include:
Also, normal behaviour is also heavily influenced by heredity:
Church Square Park
Church Square Park is a park in Hoboken, New Jersey between Garden Street and Willow Avenue and 5th and 6th Streets. The Hoboken Public Library is on its north side.
Supply
In economics, supply is the amount of something that companies are willing to provide in a market. The law of supply and demand will decide the price at which something will be bought and sold.
According to C.R. McConnell and S.L.Brue, a "supply" is a scale showing the amount of a good or service that sellers offer for sale in the market at different prices for a while
"The volume of supply" (volume of output) is the number of goods that a commodity producer (enterprise, firm) is ready to offer at a certain price for a certain period, all other things being equal.
"Amount of supply" is the amount of a product or service that is on sale at a certain price at a certain time.
It is possible to consider both an "individual supply" (the offer of a specific seller) and the total value of the supply (the offer of all sellers present on the market). In economics, it is mainly the total value of the supply for a product or service that is studied.
The "law of supply" is a direct relationship between the price and the value of the supply of goods or services during a certain period.
The increase in prices leads to additional profit, allowing the manufacturer to expand production, attracting new manufacturers to the market.
The manufacturer's main task is to solve the problem — how much product to make at a given price. There are 2 general ideas:
Various factors can make a seller more or less willing to produce and sell a good. The more common ones are:
There may be other factors that affect the supply of a good, especially since it depends on whether the seller is willing to produce and sell the good.
Demand
Demand is the total amount of goods or services which people want to buy, for a set price. The demand for an item indicates how much it is needed or wanted. This is important in economics, because the law of supply and demand will decide the price at which something will be bought and sold.
Demand is the amount of goods that people want to buy at a given price. Prices go up when supply is less, and demand is more. It follows the law of demand where as price increases, demand decreases and vice versa showing an inverse relationship between quantity demanded and price. This is known as the law of demand which assumes that the consumer will want more. Demand forecasting tries to predict how demand will change in the future.
Sometimes the demand does not change much no matter what the price is. One example is when people are addicted to illegal drugs. These people need to get their drugs, they will pay any price they can afford. This effect is known as elasticity.
Transaction
A transaction is an exchange. Money, goods, and services are often exchanged. They are bought, sold or traded.
A bank transaction is when money is taken out of or put into a bank.
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