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Pedigree Analysis

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What's a pedigree?

When you are talking about a pedigree dog, it means the dog is purebred. Through selective breeding, the dog has all the traits of that particular breed. When talking about genetics, however, a pedigree is a chart that helps show family relationships.

Pedigree Analysis

A pedigree is a chart that shows the inheritance of a trait over several generations. A pedigree is commonly created for families, and it outlines the inheritance patterns of genetic disorders.

Pictured below is a pedigree displaying recessive inheritance of a disorder through three generations ( Figure below ). From studying a pedigree, scientists can determine the following:

  • If the trait is sex-linked (on the X or Y chromosome) or autosomal (on a chromosome that does not determine sex).
  • If the trait is inherited in a dominant or recessive fashion.

Sometimes pedigrees can also help determine whether individuals with the trait are heterozygous or homozygous.

In a pedigree, squares symbolize males, and circles represent females. A horizontal line joining a male and female indicates that the couple had offspring. Vertical lines indicate offspring which are listed left to right, in order of birth. Shading of the circle or square indicates an individual who has the trait being traced. In this pedigree, the inheritance of the recessive trait is being traced. A is the dominant allele, and a is the recessive allele.

Vocabulary

  • autosomal : On any chromosome other than the sex chromosomes.
  • pedigree : Chart which shows the inheritance of a trait over several generations.
  • sex-linked : On the X or Y chromosome.

Summary

  • A pedigree is a chart which shows the inheritance of a trait over several generations.
  • From studying a pedigree, scientists can determine if a trait is sex-linked or autosomal.

Practice

Use the resource below to answer the questions that follow.

  1. What is Whirling Disorder?
  2. On the pedigree, which individuals have Whirling Disorder?
  3. Individual 5 does not have Whirling disorder, but what colored pieces does it have that potentially could have carried the gene for Whirling Disorder?
  4. Which puzzle piece (gene) is responsible for Whirling Disorder?

Review

  1. What is a pedigree?
  2. How might a pedigree aid a scientist?

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