A woman has just had twins, a boy and a girl. The woman\'s father has two X-link
ID: 261946 • Letter: A
Question
A woman has just had twins, a boy and a girl. The woman's father has two X-linked recessive disorders, haemophilia and colour-blindness, but the woman is unaffected. The father of the children has neither disorder. Both disorders are completely penetrant. The loci for the two traits are known to be 5cM apart. a) What is the probability that the boy will be colour-blind but not haemophilic? Explain your answer, including showing the genotypes and phenotypes of the family. [10 marks b) What is the probability that the girl will be unaffected (i.e. not haemophilic and not colour-blind)? Explain your answer. 12 marks]Explanation / Answer
The woman described in the given data is the daughter of a hemophilic and color blind father. both of these diseases are X-linked or sex-linked recessive diseases.
As the woman was described as unaffected, she must be carrier only. i.e., out of both of her X-chromosomes one is having the alleles for hemophilia and colorblindness on two different loci, which are 5 centi Morgan apart.
the other X-chromosome is a free X-chromosome on which the genes for color blindness or hemophilia are not there.
while forming gametes
condition 1.
if no recombination does not result in the separation of the alleles for hemophilia and colorblind ness into separate chromosomes, then only 50% of her gametes contain the alleles for both the diseases,
condition 2.
otherwise the gametes will contain the genes for both hemophilia and color blindness in random ratio but not in specified ratio
in conditon 1 the probability of getting both the diseases is there in 50% ratio in her sons.
in condition 2, as the presence of the alleles for both the diseases is not exactly determined, the occurence of one disease and the absence of another disease cannot be expected in a particular ratio.
In either of the conditions the daughter will not be competely affected even in terms of becoming carrier in 50% ratio for both the diseases in condition 1 or becoming carrier for any one disease or for both the diseases in some unspecified ratio in the condition 2
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.