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Pedigree Analysis

Explains how charts are used to study the inheritance of traits.

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Pedigree Analysis

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 and traits. A pedigree can help predict the probability that offspring will inherit a genetic disorder.

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 (two different alleles) or homozygous (two of the same allele). Some points to keep in mind when analyzing a pedigree are:

  1. With autosomal recessive inheritance, all affected individuals will be homozygous recessive.
  2. With dominant inheritance, all affected individuals will have at least one dominant allele. They will be either homozygous dominant or heterozygous.
  3. With sex-linked inheritance, more males (XY) than females (XX) usually have the trait. Sex-linked inheritance is usually recessive. 

Symbols of a pedigree, and an example pedigree

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.

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.

Explore More

Use the resource below to answer the questions that follow.

  1. What is Whirling Disorder?
  2. Is Whirling Dosorder inherited in a dominant or recessive mannor? Why?
  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? From whom did he inherit these pieces.
  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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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.

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