Question

In Drosophila, the allele for a normal grey body color G is dominant to ebony body & The following table summarises the results of several crosses.

S.No	Cross	Result
	Strain 1*gg	All wild type
	Strain 2*gg	1 wild type 1 ebony
	Stain 3*gg	All ebony
	Stain 4*Gg 3	3 wild type 1 ebony

Which strain both have the genotype Gg?
A. 1 and 3
B. 1 and 4
C. 2 and 3
D. 2 and 4

Answer 1

Hint: In Drosophila, the crossing involves the F 1 hybrid with the double recessive genotype. A test cross is a test which was introduced by Gregor Mendel, it is a test where the genotype of an organism showing the dominant phenotype is determined.

Complete answer:
The first cross which is in between the strain, 1 and gg will result in all wild-type offspring where it must be having the genotype GG. In this case, all the offspring will consist of genotype Gg which shows wild type character. In strain 3 the genotype gg will result in all offspring having an ebony body. Whereas strains 2 and 4 consist of genotype Gg. The cross for the strain 2*gg can be represented as:
gamete type g g
G Gg Gg
g gg gg
where it is seen that the offspring has 1 wild type and 1 ebony body which is grey as G is dominant. The cross for 4*Gg can be represented as:
gamete type G g
G GG Gg
g Gg gg
where it can be seen that the offspring has 3 wild types and 1 ebony body which is grey.
Hence, the correct option is ‘D’ 2 and 4

Note: The first strain which is the cross for the strain 1*gg will have the genotype GG and the cross for strain 3*gg the genotype will be gg, where in the first strain the result will be all wild type offspring and in the cross 3*gg the offspring will be having an ebony body.