Overview:
It is thought that in nature certain "favorable" genetic variations allow those with the trait to better take advantage of unexploited habitats. Simply stated, those individuals are better able to survive, reproduce, and pass on the trait to their offspring. A Pedigree is one way to show the history of a certain genetic trait within a family. Some human traits,like free earlobes and attached earlobes, seem to be controlled by a single pair of genes. Genes can be either dominant or recessive. Genetically, the dominant trait is more likely to show up than the recessive trait. The gene for free earlobes is dominant over that of attached earlobes. In this activity you will make a pedigree chart for earlobe type in your family.
Free earlobe 
Attached earlobe 
Sample Pedigree Chart:
Background:
In the sample Pedigree chart above, a male and female married and had four children, two boys and two girls. One of these children married, and this couple in turn had two children, one boy and one girl. The individuals whose symbols are darkened show the trait that is being investigated, while the clear symbols represent individuals who do not show this trait.
Some human traits, like free earlobes and attached earlobes, seem to be controlled by a single pair of genes ,which are either dominant or recessive. The gene for free earlobes is dominant (represented with a capital "L") over that of attached earlobes ("l").
The two copies of a gene for a specific trait are called alleles. An allele whose effect is expressed in the phenotype (physically able to be seen) even in the presence of a recessive allele is called dominant. Thus, if allele A is dominant to allele a, then AA and Aa have the same phenotype. An allele is recessive when its effect is expressed in the phenotype of the organism only in the presence of another identical allele (e.g., aa).
