Biology 2010 Student Edition

Published by Prentice Hall
ISBN 10: 9780133669510
ISBN 13: 978-0-13366-951-0

Chapter 14, Human Heredity - Assessment - 14.1 Human Chromosomes - Understand Key Concepts/Think Critically - Page 412: 6


The mother can be either $X^{c}X^{c}$ or $X^{C}X^{c}$. The father could be either $X^{c}Y$ or $X^{C}Y$.

Work Step by Step

The mother can be $X^{c}X^{c}$, meaning she is homozygous recessive for the colorblindness gene and is colorblind because she has the colorblindness gene on both of her X chromosomes. She also can be $X^{C}X^{c}$, which means she is only a carrier and has the colorblindness gene only on one X chromosome whereas the other X chromosome has the normal gene that is expressed and masks the effects of the colorblindness gene. The male child only needs to inherit the colorblindness gene from one of his mother's chromosomes to be colorblind. The father could be either $X^{c}Y$ or $X^{C}Y$ because even if the father were colorblind and had the colorblindness gene on his single X chromosome, he could not pass his colorblindness gene on to male offspring because he only contributes the Y chromosome to his male offspring, and the Y chromosome does not carry the colorblindness gene at all.
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