When researchers cross a fluidly Drosophila melanogaster wit

When researchers cross a fluidly (Drosophila melanogaster) with scalloped-shaped wings with a true breeding wild type fly with normal wings, 87 of the offspring have scalloped wings and 90 have normal wings. If they cross two flies with scalloped-shaped wings, 133 of the offspring have scallop-shaped wings and 67 have normal wings. Explain these results and draw the Punned squares. Use for the normal allele and for the scalloped allele. In the silkworm, translucent skin (Z^od) is recessive to the opaque skin (Z*) and is a Z-linked phenotype. a. What is the difference between a ZZ-ZW and XX-XY sex determination system? Can a female silkworm inherit the Z^od allele from her father or mother or both? Can a male silkworm inherit the allele from his father or mother or both?

Solution

2.(a) Most creatures from human to fruit flies have the X and Y chromosomes while birds, butterflies, silkworm, snakes, etc have ZW chromosomes instead. There are many differences between XY and ZW sex determination system.

They do not share any genes at all. Moreover, they flip the sex determination system. The male sex has a ZZ chromosome while the female sex has a ZW chromosome. In one system males are heterogametic, with XY chromosomes, and in the other system they are homogametic, with ZZ chromosomes. This may be due to strenuous male competition in animals with the the ZW system. There\'s sexual competition in most species, of course, but XY males compete in a way that demonstrates overall fitness, while ZZ males compete in a way that demonstrates traits which make them fit as a male, but would be disastrous for females. The most dramatic example is the peacock. The males\' stunning tails help them attract mates, but if the tail were inherited by a female it would get her eaten by a predator.