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6th Grade Science / Lesson 8 - Pedigree

What will we be learning today?

  • In this lesson, we are going to learn all about what is a pedigree.

What Is a Pedigree?

  • Do you know what a pedigreed dog or cat is? It is an animal that has a family line that is recorded so that a given trait can be traced from parents back to grandparents and great-grandparents.

  • A pedigree is a chart used to trace the history of traits in a family. A pedigree shows which members of the family have a particular trait, such as curly hair, long eyelashes, or attached earlobes.

Symbols are used to make a pedigree.

  • Shaded shapes stand for individuals who show a form of a particular trait, such as curly hair.

  • Unshaded shapes stand for individuals who do not have that form of the trait.

  • Circles are females, and squares are males

  • A square and circle connected by a horizontal line stands for male and female parents.

  • A vertical line connects parents to their offspring

  • All the children in the family are also connected by a horizontal line. The oldest child is always at the left, and the youngest at the right

In a pedigree some individuals are called carriers . A carrier is an individual who has inherited the factor for a particular trait but who does not show that trait. For example, the pedigree here shows that the mother has curly hair. The father does, too. Of their four children, three have curly hair and one has straight hair. Both of the parents must be carriers of the factor for straight hair.

If you know that the inherited factor for straight hair is recessive, the pedigree tells you that both parents must be carriers of the straight hair factor.

The pedigree on the slide before, traces short eyelashes in three generations of an imaginary family. By analyzing the chart, you can tell which family members might be carriers of the recessive factor for short eyelashes. First, look at the parents' generation. Since the father has short eyelashes, he must have two recessive factors for eyelash length (ll). The father must have passed on one recessive factor to each child. Since the mother has long eyelashes, the pedigree cannot tell us whether she carries two dominant factors for eyelash length (LL) or one dominant and one recessive factor (Ll).

Second, look at the children's generation. No child has short eyelashes. However, since each child received one recessive factor from the father, all three children in this family must be carriers of the recessive factor for short eyelashes (Ll).

Third, look at the grandchildren's generation. One of Sara's children has short eyelashes. One of John's does, too. This tells us that both Sara and John, and their mates, must be carriers of the recessive factor. Since neither of Susan's children has short eyelashes, the pedigree cannot tell us whether or not their father is a carrier.

Let's Review What We Learned Today!

  • Now complete your worksheet!