Question

One type of colorblindness is a recessive, sex-linked trait that is carried on the X chromosome. If a colorblind woman and a man who is not colorblind had children, what chance would there be that their son would be colorblind?

Answer 1

You can create a Punnett square knowing what you told us

Answer 2

Oh, if it's carried on the X chromosome then nevermind

Answer 3

Wait...maybe

Answer 4

I'm confused now too, sorry bud

Answer 5

it's carried on the X chromosome and the mom is colourblind X(c)X(c) and the dad isn't colourblind X(C)Y. So we can agree that the dad does not carry it and can't inherit it, we can ignore his genetic contribution.

The son must have X(c)Y, since the only X contribution is the mom and she has both recessive X's, i.e. X(c), all the sons will be colourblind.

Answer 6

Do you already know how WOMEN are (X X)
and MEN are (X Y) ?

That's pretty basic.

---------------------

Here's another basic fact:

The alleles (letters) for sex-linked diseases can ONLY be carried on the X chromosome.

You'll see what I mean, soon.

---------------------

First thing we need to know is the BIG FACT:

*** The disease is RECESSIVE. So, if your genotype DOES NOT have any Capital A's,
then you are colorblind. ***

---------------------

Okay so let's look at what we know.


1. The mom is colorblind.

So this is her genotype:

\[X_{a}X_{a}\]

She doesn't have any Capital A's in her genotype, see?
She only has two lowercase a's.

That's why she's colorblind.

------------------------

2. The dad is NOT colorblind.

So here is his genotype:

\[X_{A}Y\]

He DOES have a Capital A in his genotype.
So, he is NOT colorblind.

------------------------

Okay, now here's the tricky part.
Try to follow along really carefully.

Here's the question:
What are the chances that the SON, of these two parents, would be colorblind?

Well, BOYS are (X Y), remember?

And when we are born,
we get one letter (X or Y) from each of our parents.

Since the child is a BOY,
he will get a ( Y ) from his dad.

Now he needs an ( X) from his mom.

His mom has 2 ( X ).

And they are both.....\[X_{a}\]

SO....in the end....the son's genotype will look like this: \[X_{a}Y\]

He got the X(a) from his mom...
and he got the Y from his dad.

You see?

And remember the BIG RULE:
If you don't have any Capital A's,
you ARE colorblind.

The son has no Capital A's.
He only has one lowercase a.
He is colorblind.