Answer:
a. F1 genotype : IiBb F1 phenotype : Hairless
F2 genotype and phenotype :
I_B_ (hairless), iiB_ (straight), iibb (bent)
b. IiBb X iiBb
Explanation:
a. Fly 1 : pure breeding straight haired : iiBB
Fly 2 : pure breeding hairless with bent genotype : IIbb
Fly 1 X Fly 2 : iiBB X IIbb = IiBb (F1)
All the offspring will be hairless since there is one dominant I allele which will inhibit hair production regardless of the type of allele of other gene.
Two F1 flies will be crossed to obtain F2 flies. IiBb X IiBb :
I_B_ : hairless = 9
I_bb : hairless = 3
iiB_ : straight hair = 3
iibb : bent hair = 1
Hairless : straight : bent will be in 12 : 3 : 1 ratio.
b. The offspring of this cross :
hairless : I_ _ _
straight : iiB_
bent : iibb
There is a bent offspring which has both the recessive alleles of both the genes. Hence it must have obtained the two alleles from the two parents. So their genotype is _i_b and _i_b.
Half of the offspring are hairless as given by the ratio. This is only possible if the cross is between Ii and ii fly:
I i
i Ii ii
i Ii ii
So the genotype is Ii_b and ii_b.
The remaining hairy flies are in 3:1 ratio of straight to bent. This is only possible if the cross is between Bb and Bb fly:
B b
B BB Bb
b Bb bb
So the final genotype of the flies is IiBb and iiBb.
