Using Pedigrees to Visualize Inheritance

Lesson Plan - Get It!

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Historians use family trees to show relationships among family members.

Scientists use a visual tool that shows genetic relationships between family members. In the previous Related Lesson, you learned about sex-linked traits that travel on the X chromosome.

Before continuing, if you missed or need to review the previous Related Lessons, find them in the right-hand sidebar.

These traits have a unique inheritance pattern different from dominant and recessive traits. All inheritance patterns can be visualized using a pedigree tool. Pedigrees are very similar to a family tree but present the information more directly, as seen in the following image.

Each horizontal line in a pedigree represents a different generation in a family. Notice how a female and male parent are connected to offspring through lines.

In a pedigree, circles represent female family members, and squares represent male family members. Notice how the pedigree above uses names to identify royal family members.

Compare the royal family pedigree above to the one below.

In both pedigrees above, you can see that the shapes have various levels of shading. This shading is essential for identifying how traits are passed from parents to offspring.

Fully shaded shapes indicate an affected individual, meaning they have the disorder. Partially shaded shapes show carriers, individuals with one recessive allele that can pass the disorder to offspring.

Empty shapes show unaffected individuals who do not have phenotypic or genotypic impacts.

Pedigrees can show inheritance patterns for dominant, recessive, and sex-linked traits. Dominant traits show up in every generation.

• Can you see how each generation below contains at least one individual with the disorder in this image?

Recessive traits skip generations, including more disorder carriers. Notice how the pedigree below shows an affected member in the first and third generations but only carriers in the second.

Sex-linked traits follow a unique pattern: males have the disorder, and females are carriers. While women can inherit a sex-linked trait, it is scarce.

Notice how males and females differ in the below pedigree.

Pedigrees are beneficial tools that show how families inherit traits. Dominant traits show up in every generation, while recessive traits skip generations.

Sex-linked traits appear in males, and female carriers are also shown. These patterns are easily distinguishable in visual format.

• How might pedigrees give you information about family genetics?

Move on to the Got It? section to learn more.