A woman with normal color vision, but her father is color blind. The woman marri
ID: 259248 • Letter: A
Question
A woman with normal color vision, but her father is color blind. The woman marries a man with normal vision, and they have a son. A "Simple Sequence Length Polymorphisms (SSLP)" is located 2 cM away from the X-linked locus responsible for red-green color blindness. Three alleles of this SSLP are known: "4 repeats," "5 repeats," and "7 repeats." Given the SSLP genotypes of the various family members shown below, what is the probability that the couple's son is not color blind? (You need all the provided information to solve this problem.) Woman's father Woman Woman's husband Couple's son SSLP genotvpe "5 repeats" "5 repeats" and "7 repeats" "3 repeats" "5 repeats"Explanation / Answer
Colour-blindness is a matter of sex linked inheritance associated with the x chromosome
Where in our case,
The women’s father is colour blind man, and his daughter may be a carrier or she may not.
Where his daughter marries a non-colour blind man and she is a carrier, she will have a 50% chance of having a colour blind son or a carrier daughter.
If she is not a carrier the line will die out with her. If their son marries a non-colour blind woman, all of his daughters will be carriers but none of his sons will be either colour blind or colour blind carriers.
Reason:
The 23rd chromosome is made up of two parts – either two X chromosomes if you are female or an X and a Y chromosome if you are male. The faulty ‘gene’ for colour blindness is found only on the X chromosome. So, for a male to be colour blind the faulty colour blindness ‘gene’ only has to appear on his X chromosome. For a female to be colour blind it must be present on both of her X chromosomes.
If a woman has only one colour blind ‘gene’ she is known as a ‘carrier’ but she won’t be colour blind. When she has a child she will give one of her X chromosomes to the child. If she gives the X chromosome with the faulty ‘gene’ to her son he will be colour blind, but if he receives the ‘good’ chromosome he won’t be colour blind.
A colour blind boy can’t receive a colour blind ‘gene’ from his father, even if his father is colour blind, because his father can only pass an X chromosome to his daughters.
A colour blind daughter therefore must have a father who is colour blind and a mother who is a carrier (who has also passed the faulty ‘gene’ to her daughter). If her father is not colour blind, a ‘carrier’ daughter won’t be colour blind. A daughter can become a carrier in one of two ways – she can acquire the ‘gene’ from a carrier mother or from a colour blind father.
This is why red/green colour blindness is far more common in men than women.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.