​The AFLP technique generates polymorphic DNA fragments that are generally scored as dominant markers. However, a pair of DNA fragments (say ‘a’ and ‘b’) generated by AFLP can be termed as co-dominant, if on analysis of a large progeny of doubled haploids (DH) derived from an F₁ cross between two parents one with fragment ‘a’ and the other with ‘b’, it is observed that:​

Correct option is B

Explanation-

AFLP markers (dominant) show polymorphism.
Two parents:
          Parent 1 has fragment ‘a’,
          Parent 2 has fragment ‘b’.
F₁ hybrid has both fragments ‘a’ and ‘b’.
Doubled haploids (DH) are produced from gametes of the F₁.

Since the F₁ has both fragments 'a' and 'b', its gametes can carry either:
                           Only fragment ‘a’, or
                           Only fragment ‘b’.
AFLP markers are dominant and presence/absence is scored, and these are usually unlinked markers.
So, the gametes of F₁ will segregate such that:
                            50% gametes will carry fragment 'a'
                           50% will carry fragment 'b'
When these gametes are used to generate doubled haploids (DH), each DH individual will be homozygous for one gamete:
                            50% of DH progeny will show only fragment ‘a’
                            50% of DH progeny will show only fragment ‘b’
                              No DH progeny will have both or none

So, the correct answer is option B-  “50% of the progeny has fragment ‘a’ and the remaining have fragment ‘b’.”

Incorrect options-
Option A - "50% of the progeny has both ‘a’ and ‘b’ fragments and the rest have none."
Each DH individual arises from a single gamete. A gamete cannot have both ‘a’ and ‘b’, because they were contributed separately by each parent and are unlinked.
So no DH will have both fragments.
Also, none of the DHs will lack both fragments—every gamete must carry either ‘a’ or ‘b’, as those were the only variants present in the F₁.
Option C - "25% of the progeny has fragment ‘a’, 50% both ‘a’ and ‘b’, and the rest fragment ‘b’."
This pattern assumes a segregation ratio of 1:2:1, which is seen in typical Mendelian diploid F₂ populations—not in doubled haploids.
In DHs:
    No heterozygotes (i.e., both ‘a’ and ‘b’)
    No  1:2:1 ratio
So this is completely inconsistent with how haploids are generated and doubled.
Option D - "75% of the progeny has both the fragments, while 25% has either ‘a’ or ‘b’."
​Again, no doubled haploid can carry both fragments. DHs are derived from a single F₁ gamete, which only carries one fragment. Thus, having 75% DHs with both fragments is not possible. Also, the ratio doesn’t match expected 1:1 segregation (i.e., 50% ‘a’, 50% ‘b’).