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

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 2gg 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 4Gg 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 1gg will have the genotype GG and the cross for strain 3gg 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.