Genetics is the study of heredity and in extension, or the application of probability in biology. Heredity is the process of transferring genes from parents to offspring. The leading person in early genetics was a monk named Gregor Mendel. He worked with pea plants and performed experiments to determine how traits appeared in them. Pea plants were a good choice to experiment on because their traits were obvious, they reproduced quickly, and mainly because they had the ability to self-pollinate which means that they could produce offspring that contained only the genes from the one single parent plant. His experiment had several stages as shown below:
- Let a certain plant with desirable traits self-pollinate over and over until all the offspring were pure for a certain trait. He named the first plants he began with the P1 generation for First Parental Generation. *Pure: Having only the genes for one trait; can only pass on the gene for that trait. For example, a pea plant pure for green seeds can only pass on a gene for green seeds and cannot pass a gene for yellow seeds.
- Cross two pure plants together to produce an offspring with mixed genes. He named this the F1 generation for First Filial Generation.
- He then self-pollinated the plants over and over and recorded the traits of the offspring.
In some cases, traits from the parent plants did not show up in the offspring generations, at least not in all of the offspring. These traits that are present but do not appear are called recessive traits. Each of different forms of a gene are called alleles. Often, two alleles are passed on from each parent. Generally, it is possible for a parent to have two dominant alleles, two recessive alleles, or one of each. One allele would represent green seeds and one would represent yellow, but both may be present in the same plant. The allele that is expressed over recessive ones are called dominant. In the punnet square at right, lower cast t's stand for recessive genes and upper case T's stand for dominant ones.
A method to determine the traits of an offspring from the genes of the parents is called a Punnet Square. Since only one allele is passed onto offspring from each parent and assuming the probability for each being passed on is 50%, this method yields the possibilities for each alternative. For a Punnet square for one simple two-allele trait, it can be expressed as follows:
More coming soon! Last updated March 21, 2012