In man, brown eyes (B) are dominant over blue eyes (b) and normal skin pigmentat

Question

In man, brown eyes (B) are dominant over blue eyes (b) and normal skin pigmentation (N) is dominant over albinism (n). A brown eyed, albino man whose mother had blue eyes and normal skin pigmentation and whose father was albino marries a blue eyed, normally pigmented woman whose father had brown eyes and was albino. (a) What is the woman's genotype? (b) What proportion of the couple's offspring would be expected to have brown eyes and normal skin pigmentation? (c) What proportion of the couple's offspring would be expected to have genotype Bbnn? (d) If the man were to marry a woman with the same genotype as his present fatherinlaw, what proportion of the offspring would be expected to have blue eyes and be albino? (e) If the woman were to marry a man with the same genotype as her present motherin-law, what proportion of the offspring would be expected to be of genotype bbNN?  

Explanation / Answer

Man's Father Genotype= Bbnn (Father is carrier for blue eye gene)

Man's Mother Genotype= bbNn (carrier for albino gene)

Man's genotype=

Bbnn      x             bbNn

(Father)                   (mother)

Gametes: Bn, bn                    bN, bn

bN

bn

Bn

BbNn

Bbnn

bn

bbNn

bbnn

               Man’s Genotype = Bbnn (Brown eye and albino)

Woman's Father Genotype = Bbnn (Brown eye and albino)

(Man)                                                    (Woman)

Gametes: Bn, bn                                   bN, bn

bN

bn

Bn

BbNn

Bbnn

bn

bbNn

bbnn

BbNn;      Brown eye and normal pigment (25%)

Bbnn       Brown eye and albino (25%)

bbNn       blue eye and normal pigmented (25%)

bbnn        blue eye and albino (25%)

25% offspring would be expected to have brown eyes and normal skin pigmentation (BbNn)

Bbnn                      x             Bbnn

(man)                                     (woman with same genotype)

Gametes                 Bn, bn

Bn

bn

Bn

BBnn

Bbnn

bn

Bbnn

bbnn

25% offspring would be expected to have genotype bbnn (blue eye and albino)

bbNn                      x             bbNn

(woman)                                 (man with same mother-in-law genotype)

Gametes:                bN, bn

bN

bn

bN

bbNN

bbNn

bn

bbNn

bbnn

25% offspring would be expected to have genotype bbNN

bN

bn

Bn

BbNn

Bbnn

bn

bbNn

bbnn

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