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In this example, Brown eyes are dominant to blue eyes.
What does the image to the left tell you about my genotype for eye color?
What is the probability that my second child will have blue eyes?
These genetic family trees are called pedigrees and they are used to determine genotypes within families. Pedigrees can be useful in determining how traits or genetic disorders are inherited as well as in predicting the probability of those traits in future offspring.
A geneticist would construct a pedigree of a particular trait, such as blue eye color, like the one below. The shaded individuals express whatever particular trait you are looking at and can be either dominant or recessive depending on the trait.
A geneticist would construct a pedigree of a particular trait, such as blue eye color, like the one below. The shaded individuals express whatever particular trait you are looking at and can be either dominant or recessive depending on the trait.
Pedigree of an autosomal recessive trait.
Basic key for pedigrees
Reading A Pedigree
Reading A Pedigree
1. Determine if the shaded trait is autosomal (chromosomes 1-22) or sex-linked (on the sex chromosomes). Sex-linked will affect primarily males.
2. Determine if the shaded trait is dominant or recessive. *see pro tips at the bottom of the page.
3. Write in the genotypes. Use a ___ or ? in places where it is not possible to determine the second allele of an individual.
Watch this and take notes! :)
Watch this and take notes! :)
Pro Tips:
1. The shaded individuals have nothing to do with dominant or recessive. If they are shaded it means that they express whatever trait you are looking at.
2. The easiest way to determine if a trait is dominant or recessive is to find two parents that are the same (both shaded or both unshaded), who have children who are different than them.
Two parents who are the same that have children who are different CAN'T BE HOMOZYGOUS RECESSIVE because they can't give their child a dominant allele they don't have. The only way two parents can be the same and have children who are different is if the parents are heterozygous.
Constructing a pedigree is a lot of trial and error. Use a pencil! ;)
Doesn't work
Works
Pedigree Practice
Pedigree Practice
Optional: This will walk you through making a pedigree based on a family history.
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