In mice, the locus coding for the beta-globin chain of hemoglobin is 1 mu. from
ID: 168359 • Letter: I
Question
In mice, the locus coding for the beta-globin chain of hemoglobin is 1 mu. from the albino locus. Assume for the moment that the same is true in humans (they are actually farther apart than this). Sickle cell results from a recessive allele of the beta-globin gene. Albinism is also an autosomal recessive disorder. A son is born to an albino man and a woman with sickle cell anemia. Draw the chromosomes of the son, showing his alleles at each locus. What kinds of gametes will the son form, and in what proportions? A daughter is born to a normal man and a woman who has both albinism and sickle cell anemia. What kinds of gametes will the daughter form, and in what proportions? If the son in (a) grows up and has children with the daughter in (c), what is the probability that a child of theirs will be an albino with sickle cell anemia?Explanation / Answer
Answer:
a. There is a 1% chance of recombination between genes A and B.
Alleles: A = Normal skin color, a = albino (recessive), B = Normal B-globin, b = sickle-cell mutation (recessive)
Albino father; sickle-cell mother: Albino male: aB / aB * Sickle female: Ab / Ab
Son: aB / Ab
So, the son is heterozygous for the two traits.
------------A---------------------b---------------
------------a---------------------B---------------
b. Given that the genes are separated by 1 m.u., parental gametes will be 99% and recombinant gametes will be 1%.
Parental gametes: aB = 49.5%
Ab = 49.5%
Recombinant gametes: ab = 0.5%
AB = 0.5%
c. Normal father; albino & sickle-cell mother: Normal male: AB/AB * Albino, sickle female: ab/ab
Daughter: AB / ab
Parental gametes: AB = 49.5%
ab = 49.5%
Recombinant gametes: Ab = 0.5%
aB = 0.5%
d. Prob (child is aa bb) = 0.5% (ab from man) . 49.5% (ab from woman)
= 0.25%
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