Science practice 132

Gregor Mendel is known for his work in genetics. He is credited with discovering how traits (characteristics) are passed from one generation to the next. After his observations of inherited traits, Mendel concluded that each organism carries two sets of information about a certain trait. If the two sets differ about the same trait, one set dominates the other. That way, information can be passed on through the generations, even if the trait is not expressed.

It has since been determined that the presence of certain traits is attributed to genes, and the different forms that genes can take, known as alleles. Dominant alleles (D) produce dominant characteristics; recessive alleles (d) produce recessive charactersitics. Dominant alleles are expressed whenever present (DD, Dd) but recessive alleles are expressed only when the dominant allele is absent (dd).

A study was done in which the independence of two traits was tested. In this study, a rabbit with long black hair was mated with a rabbit with short white hair. The dominant trait for hair length is short (H). The dominant trait for hair color is black (B). If the two initial rabbits (level 1 in the figure below) are homozygous for their traits, meaning that the two alleles for each trait are the same, breeding them will result in offspring that have both a dominant and recessive allele for each trait. Such a pairing of alleles is known as heterozygous. If, as in level 2 of the figure, two heterozygous rabbits are bred, the chart (level 3) contains all the possibilities for their offspring.