In chickens, a single mutation has a dominant effect on neck feathers (causing the chickens to...
In chickens, a single mutation has a dominant effect on neck feathers (causing the chickens to have "naked necks") and a recessive effect on viability (causing the chickens to die early). Let N be the mutant allele and n the wild-type allele.
A) Male chickens with naked necks are crossed to females with normal neck feathers. Think about the genotypes of those chickens. Among the F1 progeny, what % naked neck versus normal neck feather adult chickens do you expect?
B) Male chickens with naked necks are crossed to females with naked necks. Among the F1 progeny, what % naked neck versus normal neck feather adult chickens do you expect?
Homework Answers
A) The naked males could be having Nn or NN genotype. If Male is NN, crossing them with normal feathered females, nn would result in all the progenies produced having Nn genotype and nacked neck characteristic.
If male is Nn and the female is nn then the cross would be
| Gametes(Females/Males) | N | n |
| n | Nn (Nacked) | nn (Normal) |
| n | Nn(Nacked) | nn (Normal) |
Here 50% of the F1 progeny will have naked neck whereas the remaining 50% will be normal.
B) Male chickens with naked necks (NN/Nn) are crossed to females with naked necks (NN/Nn)
If males are NN and females are also NN, all the F1 progenies will also be NN and will have nacked neck.
If males are NN and females are Nn or vice versa, then again all the progenies will be showing naked neck.
| Gametes(Females/Males) | N | N |
| N | NN(Nacked) | NN(Nacked) |
| n | Nn(Nacked) | Nn(Nacked) |
If both males and females are Nn, then 25% will be Normal and 75% will be nacked.
| Gametes(Females/Males) | N | n |
| N | NN (Nacked) | Nn (Nacked) |
| n | Nn(Nacked) | nn (Normal) |
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