A female who does not carry the colorblindness allele has children with a male who is colorblind?

Question

A female who does not carry the colorblindness allele has children with a male who is colorblind. What proportion of their children will be colorblind?

all
1/4
1/2
3/4
none

Answer 1

None of them.

The gene usually referred to when talking about colourblindness happens to lie on the X sex-chromosome. The mother has two Xs without it and the father has one X with the gene and one Y which can't carry it.

Since any child who gets the father's colourblind X gene must also get a normal X from the mother and colourblindness is recessive, none of the children will show the trait of colourblindness. All of the girls, however, will carry the gene and none of the boys will.

Answer 2

The colour blindness allele is carried on the X chromosome.

The allele is recessive. Consider that X^C represents the normal, dominant allele, X^c is the allele for colour blindness and the Y chromosome carries neither, Y^o

For a female to be colour blind, she must have the genotype X^c X^c, meaning both parents must carry the gene. In this case, they do not.

A female can be homozygous normal, X^C X^C, heterozygous (a carrier), X^C X^c, or homozygous recessive, X^c X^c.

A male can be homozygous normal, X^C Y^o, or homozygous recessive, X^c Y^o.

Since the father is colour blind, he must be X^c Y^o. The mother is homozygous normal, she is X^C X^C.

So the possible offspring genotypes are:

X^C X^c female carrier, 50%
X^C Y^o normal male, 50 %

No offspring are colour blind.

Answer 3

1/4

Answer 4

None. Colorblindness is carried on the X chromosome and is recessive. So if you do the punnett square, where Xc is the colorblind allele and XC is the normal allele...

.........XC... ..XC
------------------------
Xc |XCXc | XCXc
Y | XCY | XCY

In all of the boys (XY), no colorblind allele is present. In all of the girls (XX), a colorblind allele is present but masked by the non-colorblind allele.

Answer 5

none, mothers' pass this gene along

Answer 6

Do your own homework