Virtual Genetics Lab: The Inheritance of Color Blindness Worksheet

Learning Goal: To explore the inheritance pattern of color blindness in humans.
Prerequisite Knowledge: Before beginning this lab, you should be familiar with these concepts: the definition of sex-linked genes, and examples of sex-linked genes in humans and other organisms how the inheritance pattern of sex-linked genes differs from that of autosomal genes the use of Punnett squares to understand patterns of inheritance
Introduction: The gene that codes for red-green color blindness, the most common form of color blindness in humans, is found on the X chromosome. One in 12 males is color blind. In females, however, color blindness affects only about 1 in 200. Why is …show more content…

Most X-linked traits in humans are recessive.

Part E
Complete the Punnett squares below to determine the possible genotypes of each couple’s male and female offspring. (X represents the normal color vision allele. X represents the color-blindness allele. Y represents the Y chromosome, which does not carry the color-vision gene.)

X X
XX
XY
XY

Couple 1

Wife

Husband

Couple 2

Wife

Husband

Couple 3

Wife

Husband

Part F
Review the results you obtained from the lab for the female offspring of all three couples. Then, look at the female offspring (the offspring with two X chromosomes) in your three Punnett squares.
What genotype must a female child have in order to be color blind?

The genotype needed for a female child to be color blind is X X.

Part G
Review the results you obtained from the lab for the male offspring of all three couples. Then, look at the male offspring (the offspring with a Y chromosome) in your three Punnett squares.
What genotype must a color-blind male have? Explain.

X Y is the genotype. The color blindness gene only exists on the X chromosome. The X chromosome must carry the color blind allele “n” in order for a male to be color blind.

Part H
Think it over
Explain why color blindness occurs more commonly in males than females.

The color blindness gene is carried only on X chromosomes, and since it is passed on by the X chromosome, that means that females that one normal