Question

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

S. No.	Cross	Result
1.	strain 1*gg	all wild-type
2.	strain 2*gg	1 wild type: 1 ebony
3.	strain 3*gg	all ebony
4.	strain 4*Gg	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

The correct option is D 2 and 4

The first cross between strain 1 and gg result in all wild-type offspring, it must have genotype GG. As in that case, all offspring will have Gg genotype hence showing wild-type character. Similarly, strain 3 must have genotype gg resulting in all ebony bodied offspring.

While, strain 2 and 4 have genotype Gg.

Cross for strain 4*Gg can be shown as:-

Gamete type	G	g
G	GG	Gg
g	Gg	gg

Here, it can be seen that offspring have 3 wild type:1 ebony as grey body ( wild type ) colour G is dominant.

Cross for strain 2*gg can be shown as:-

Gamete type	g	g
G	Gg	Gg
g	gg	gg

Here, it can be seen that offspring have 1 wild type: 1 ebony as grey body ( wild type ) colour G is dominant. So, the correct option is '2 and 4'.