GS Activity: HH Thumb (Student Version)

Name ________________________ Date ___________________

Hitchhiker's Thumb Activity: Understanding how a trait can skip generations

GenScope File: HHThumb.gs

The file opens with the pedigree window showing. The pedigree shows hitchhiker's thumb for Jack, Jill, their children and their grandchildren. Hitchhiker's thumb is an autosomal, recessive condition (tt = hitchhiker's thumb, T = non-hitchhiker's thumb).

How come none of Jack and Jill's kids have hitchhiker's thumb but one of their grandchildren does???

Here are some questions that will help you get started:

1. What is Jim's genotype for hitchhiker's thumb? Circle the right answer.

TT     Tt     tt     T-     t- 2.       What must Erica's and Bob's genotypes be? Circle the right answer. TT     Tt     tt     T-     t- 3.       What is Jack's genotype for hitchhiker's thumb? TT     Tt     tt     T-     t- 4.       What is Jill's genotype for hitchhiker's thumb likely to be? (Hint: none of their children has the trait.)
TT     Tt     tt     T-     t- 5.       If Jack and Jill have 12 more children, how many do you think will have hitchhiker's thumb? (circle one) None
3 or 4
About half
All of them 6.       If Erica and Bob have 12 more children, how many do you think will have hitchhiker's thumb? (circle one) None
3 or 4
About half
All of them 7.       OK - now try it on GenScope. Open the file HHThumb.gs and check out the chromosomes. Also, give Jack and Jill and Erica and Bob some more kids and see if you made the right predictions.

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