PLEASE SHOW WORK For the next problem, assume that brown eyes (B) are dominant o

Question

PLEASE SHOW WORK

For the next problem, assume that brown eyes (B) are dominant over blue eyes (b), and right-handedness (R) is dominant over left-handedness (r). (In reality, modifying factors complicate the inheritance of these traits) A right-handed, blue-eyed man marries a right-handed, brown-eyed woman. They have two children, one left-handed and brown-eyed and the other right-handed and blue-eyed. By a later marriage with another woman who is also right-handed and brown-eyed, the man has nine children, all of whom are right-handed and brown-eyed. What are the genotypes of this man and his two wives?

Explanation / Answer

Answer:

Based on the information provided:

Brown eyes (B) are dominant over blue eyes (b)

Right handedness (R) is dominant over left handedness (r)

Man - Right handed, blue-eyed man (genotype = bbR_)

*empty space could be both dominant or recessive allele as it wont change the phenotype

marries a right handed, brown eyed woman (genotype = B_R_)

1) 2 children - one left handed and brown eyed (genotype = B_rr) - This is only possible if both father and mother carries a recessive left handed allele (r) so their genotype with respect handedness will be Rr

and second children right handed and blue -eyed (bbR_) - this is only possible if the first wife genotype for eye color is hetergozygous i.e. Bb and heterozgous for handedness Rr

2) later marriage with another woman - right handed and brown eyed (genotype = B_R_)

- 9 children - all right handed and brown eyed (genotype = B_R_)

Since father's genotype is bbRr and all the children from second wife carry atleast one dominant allele for brown eyes, therefore second wife should be homozygous dominant for eye color (BB). If she was heterozygous for eye color than atleast one or few children should have carried one recessive allele from her and in that case the children would have been blue eyed. But since none of the children has blue eyes that means second wife is homozygous dominant for eye color.

On a similar lines, with the same reasoning the second wife would also be homozygous dominant for handedness (RR).

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