Question

I'm stuck with this genetics problem! >.<

A normal woman whose mother is colorblind marries a man whose mother was also colorblind..
What phenotype proportion can be expected in their next generation?

I have to do it by making genetic cross..:I

But, what are the genotypes of man and woman?
They both have normal genotypes?? :/ Can someone explain me please...

Answer 1

You need to find the allele composition of the colorblind phenotype. Is the condition caused by a dominant allele or a pair of homozygous recessive alleles?
This website might help: http://genetics.thetech.org/ask/ask80

Answer 2

>.>

Answer 3

The key point is that color blindness is X linked and recessive. That is, the child is only color blind when all their X chromosomes have the mutant color blind allele (version of the gene) on it. For a girl with two X chromosomes, that means that both those X chromosomes have the color blind allele. For a boy, with only one X chromosome, that means that he has only one recessive color blind allele.

The next thing you need to do is get a notation. I write Y for the male chromosome, X+ for the normal (wild type) X carried allele, and X- for the recessive color blind allele. You may use whatever notation you like.

Then figure out as much as you can about the genotypes of the parents. For example, you are told that the woman's and man's mothers, females with two X chromosomes, are color blind. Therefore, the woman's and man's mother' genotypes must be X- X-.

Next try to figure out what the man's and woman's genotypes must be, based on the fact that she is normal (not color blind), and the fact that the man got one X chromosome from his mother and a Y chromosome (because he is a male) from his Dad...

Answer 4

Do you get it yet?

Answer 5

So that woman must be a carrier ?? :/
And that man...? His mother is also colorblind...But he wouldn't be colorblind right?

:c

Answer 6

I got NOTHING ...I think ....:(

Answer 7

Yes, the woman is a carrier.

Her mother is colorblind.

That means her mother's genotype is X(a) X(a)

So, the woman got one X(a) from her mother.
That means she's a carrier.

Answer 8

The man, whose mother is colorblind,
he is ALSO colorblind.

Answer 9

So, I crossed them and got 1 girl is normal, 1 is colorblind
1 boy is normal one is colorblind.

So would it be 25% normal and 25 % colorblind girls and boys?

What I'm doing is right or wrong? :I

That's what phenotype proportion is? :c

Answer 10

ALL I have done is WRONG? I think..

I'm so confused with these problems...:I

Answer 11

You did it right.

Answer 12

Answer is 25% normal but carrier girls and 25% colorblind girls and 25% normal boysand 25% colorblind boys.