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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?

  1. 1 and 3

  2. 1 and 4

  3. 2 and 3

  4. 2 and 4
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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'.