pedigree chart
A pedigree chart is ike a family tree that shows the family members genotypes and phenotypes regarding a certain trait.
image source: http://en.wikipedia.org/
In the pedigree chart to the left, information about the genotypes and phenotypes of ancestors concerning an x-linked recessive trait is given. The circles represent females and the squares represent males. A horizontal line between a male and a female means that they had children together. the verticle lines connect parents and children, and the children are placed in chronological order left to right by birth date.
As the chart shows, the mother is a carrier of the disease. This lets us know that the mothers phenotype unaffected and that her genotype is heterozygous dominant (because the disease is recessive). The father is not affected at all. The first child is a carrier, so we know that her phenotype and genotype are the same as her mothers. Their second child is affected by the disease. This means that he must have inherited the recessive allele for the disease from his mother onto his one and only X chromosome. The third child is unaffected, meaning he inherited the dominant trait. Pedigree charts are helpful when you're trying to trace a hereditary disease or trait back through the ages. By looking at the chart and the key, you are able to tell what the ancestors phenotypes are and infer their genotypes.
As the chart shows, the mother is a carrier of the disease. This lets us know that the mothers phenotype unaffected and that her genotype is heterozygous dominant (because the disease is recessive). The father is not affected at all. The first child is a carrier, so we know that her phenotype and genotype are the same as her mothers. Their second child is affected by the disease. This means that he must have inherited the recessive allele for the disease from his mother onto his one and only X chromosome. The third child is unaffected, meaning he inherited the dominant trait. Pedigree charts are helpful when you're trying to trace a hereditary disease or trait back through the ages. By looking at the chart and the key, you are able to tell what the ancestors phenotypes are and infer their genotypes.