Question

trait a, which is x - linked, is related to colorblindness. a is considered wild - type and is dominant to a.
women with one (x^a x^a) or two (x^a x^a) dominant alleles have normal vision. women with two recessive alleles (x^a x^a) are colorblind.
men who have one dominant allele (x^a y) have normal vision. however, men with one recessive allele (x^a y) are colorblind.
use the results of the punnett square below to answer the question.

what is the phenotypic ratio of normal to colorblind people?
2:1
1:1
3:1
1:3

(here is a punnett square:
row 1 (top) has x^a and x^a as column headers.
row 1 (left) has x^a and y as row headers.
the cells are:
x^a (row) and x^a (column): x^a x^a
x^a (row) and x^a (column): x^a x^a
y (row) and x^a (column): x^a y
y (row) and x^a (column): x^a y )

Explanation:

Step1: Identify Genotypes

From the Punnett square, the genotypes are $X^A X^A$, $X^A X^a$, $X^A Y$, $X^a Y$.

Step2: Determine Phenotypes

• $X^A X^A$: Normal (female)
• $X^A X^a$: Normal (female)
• $X^A Y$: Normal (male)
• $X^a Y$: Colorblind (male)

So, normal phenotypes: 3, colorblind: 1.

Answer:

3:1