Lesson Plan - Get It!
What is a way you can map out or display your family line?
Historians use family trees to show relationships among family members.
Scientists use a different kind of 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 that of dominant and recessive traits. All inheritance patterns can be visualized using a tool called a "pedigree." Pedigrees are very similar to a family tree, but present the information in a more direct way as seen in the following image:
Image by CKRobinson, via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.
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 members of the royal family. Compare the royal family pedigree above to the one below:
Image self-created by Rozzychan and adapted by Huijts, via Wikipedia, is licensed under the Creative Commons Attribution-ShareAlike 3.0 license.
In both pedigrees above, you can see that the shapes have various levels of shading. This shading is important for identifying how traits are passed from parents to offspring. Fully-shaded shapes indicate an affected individual, meaning that they have the disorder. Partially-shaded shapes show carriers, individuals who carry 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 — see how each generation below contains at least one individual with the disorder in this image?
Image by Jerome Walker, via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Recessive traits skip generations, and include more carriers for the disorder. Notice how the pedigree below, provided by Genome Research Limited, shows an affected member in the first and third generation, but only carriers in the second:
Image by yourgenome, Genome Research Limited, is licensed under a Creative Commons Attribution 4.0 CC-BY license.
Sex-linked traits follow a unique pattern, where males have the disorder and females are carriers. While it is possible for women to inherit a sex linked trait, it is very rare. Notice how males and females are different in the pedigree below:
Image by Simon Caulton, via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Pedigrees are very helpful tools that show how traits are inherited through families. Dominant traits show up in every generation, while recessive traits skip generations. Sex-linked traits show up 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?
Discuss what you have learned with a parent or teacher before moving to the Got It? section of this lesson.