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Step 1
Gather information. Learn the eye colors of as many family members as possible from at least three generations. Tip: Reduce the information to "dominant" or "recessive": pigmented eyes or blue eyes. For example: Grandma: pigmented; Grandpa: pigmented. Mom: pigmented; Dad: blue. Sister: pigmented; Brother: blue.
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Step 2
Represent males on your chart by squares and females by circles. Represent the dominant trait by one color and the recessive by another, or leave clear. For example, represent Grandma with pigmented eyes, by a brown circle. Represent Dad, with blue eyes, by a blue square.
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Step 3
Arrange the shapes with each generation on a different line: the oldest generation at the top of the page, the second generation in the middle, and the youngest generation at the bottom.
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Step 4
Represent marriages by a horizontal line connecting husband and wife. For example: Connect Grandpa's square and Grandma's circle by a horizontal line.
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Step 5
Represent children by a vertical line descending from the parents' marriage line. For example: Draw a line down from Grandpa and Grandma's marriage line, putting Mom's circle there. Draw a line down from Mom and Dad's marriage line, add a crossbar (forming an upside-down T) with small vertical lines coming off each end, and put a circle and a square below these lines to represent Sister and Brother.
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Step 6
Now, analyze your chart. Can you figure out what genes each person has? Tip: Look at the recessives first. With rare exceptions, people showing the recessive trait (blue eyes) must have two recessive genes. Since they received one gene from each parent, each of their parents has at least one recessive gene. They must pass recessive genes on to their children, so each of their children has at least one recessive gene.
People showing the dominant trait (pigmented eyes) may have two dominant genes or one dominant and one recessive. It is not always possible to determine what genes a dominant-trait person has.
