Campbell Biology (11th Edition)

Published by Pearson
ISBN 10: 0-13409-341-0
ISBN 13: 978-0-13409-341-3

Chapter 15 - 15.2 - Concept Check - Page 300: 2


50% if the second child is a boy, 0% if the second child is a girl. Overall, 25% chance.

Work Step by Step

Here, make a Punnett square for a monohybrid cross. Since the trait is sex-linked and Tim lacks it, he must be D- (one allele for normal dystrophin, one non-allele on his Y chromosome), and Rhoda must be Dd. Her d allele passed to the first child born. Girls will always get Tim's D allele and not have the disease while boys have a 50% chance of getting the d allele and a 50% chance of getting the D allele.
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