If men cannot pass colour blindness onto sons,only daughters then why is my boyfriend and his dad colour blind

Question

I am so confused!!

My boyfriends dad is colour blind and he thinks he got it from his dad...and i am trying to explain that men cannot pass it onto sons only daughters....what i also dont understand is that my boyfriend also has a younger brother who isnt colour blind and a sister who isnt either but i suspect she is a carrier.

I know that Men cannot pass on colour blindness to their sons...only to their daughters who are usually carriers. But why is my boyfriend and his dad the colour blind people in the family? Could his mum have the gene and not know it?

Can someone explain how this happened please!!

Answer 1

The color blindness gene is recessive and is only carried by the X chromosome of a female. So a male which is s*x a pair chromosome XY. If the mother carries the gene and it is pass to her son he will be colorblind. This is because the Y chromosome does not carry it so the recessive gene will be dominate in this case because there nothing to cancel it out. In the case of a daughter the pair is XX one from the farther and one from the mother so both X chromosomes would have to be recessive for the daughter to be color blind. Which is not very common.

Answer 2

And, just to add a bit to H37Rv's answer (which is absolutely correct by the way) - it is simply a coincidence that both your boyfriend and his father are colour blind. You've heard how your boyfriend got his colour blind gene, and how it had nothing to do with his father and, if you think about it, his father must have got his colour blind gene from his mother too (i.e. your boyfriend's grandmother). So it is simply a coincidence that both your boyfriend's paternal grandmother and his mother carried the gene.

Answer 3

The simple answer is yes, mum is a carrier.  

Dads, to have sons, by definition pass on their Y chromosome instead of their X.  The gene for color blindness is on the X chromosome, which boys ALWAYS get from their mother. So the color blindness allele had to have come from the mother, who has two X chromosomes one carrying a "good" and the other a "color blind" copy of the gene.

So for the brother, mom passed on her "good" allele, she can pass on either with a 50% probability. And for sis she also passed on the "good" allele.  But sis definitely carries the gene for color blindness because dad gave her his entire X chromosome which carries the color blindness gene. Mom passed on her "good" allele to sis, or else she would be one of those rare color blind females.

Your main question confuses causation and correlation. Remember, sometime things happen by chance, father and son being color blind is one of those chance occurrences.   Although I could imagine a situation on an early date where mom and dad have something to talk about. "Oh, you're color blind? so is my dad..."

Answer 4

color blindness are found only in males...

i think it's transmitted in males 2..