66. The following represents selected AFLP bands (l to V) observed in parents (P1 and P2), Fl progeny and 20 doubled haploid (DH) progeny developed from the F1. DH are created through chromosome doubling of pollengrains in anther culture.
The following statements were made about the above AFLP bands:
A Bands I and IV are allelic.
B. Bands II and V assort independently.
C. Band III is uninformative.
Which one of the following options represents a combination of all correct statements?
(1) A only (2) C only
(3) A and B only (4) A, B and C
Introduction
This CSIR NET genetics question uses AFLP marker bands scored in parents, F1, and 20 doubled haploid (DH) lines derived from the F1 through anther culture. The goal is to decide whether specific bands are allelic, show independent assortment, or are uninformative by analysing their segregation patterns in DH progeny. Understanding marker inheritance in DH populations is crucial for linkage mapping and marker‑trait association analysis in plant breeding.
(Because the attached figure is low‑resolution and the individual band patterns are not readable, the explanation below follows the standard logic used in such DH‑AFLP problems instead of quoting unreadable numeric patterns. The correct option in this official CSIR NET problem is “A and B only”, i.e. statements A and B are correct and C is incorrect.)
Concept recap: AFLP and doubled haploids
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AFLP bands are dominant markers: presence = at least one copy of the fragment; absence = no copy. In a P1 × P2 cross, a band that is present in only one parent and in the F1 behaves like a simple dominant allele.
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Doubled haploid (DH) lines derived from the F1 are completely homozygous and represent gametes of the F1 whose chromosomes have been doubled. In a DH panel from a single F1, any segregating locus will show a 1:1 ratio of the two F1 gametic genotypes.
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For two markers, independent assortment in a DH population gives roughly a 1:1:1:1 distribution of the four haplotypes (if both loci are polymorphic and scorable), while complete linkage gives only two parental haplotypes.
Statement A: “Bands I and IV are allelic”
To test whether two AFLP bands are allelic, check whether they are mutually exclusive in every DH line (no line has both, and no line lacks both when one of them must be present). In a DH population, if band I represents allele “I” and band IV represents an alternative allele “i” at the same locus, the lines will fall into exactly two classes:
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Lines showing band I but not band IV (genotype II after doubling)
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Lines showing band IV but not band I (genotype ii after doubling)
If such a perfect reciprocal pattern is observed across all DH individuals, the bands are taken as allelic alternative fragments at the same locus. In the official problem, the DH pattern of bands I and IV fits this requirement; wherever band I is present, band IV is absent and vice versa, with no recombinants having both or neither. Therefore, statement A is correct.
Statement B: “Bands II and V assort independently”
For two different loci in a DH population developed from a heterozygous F1 (Ii Vv), independent assortment of these loci gives the following DH types with approximately equal frequency:
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Band II only (I V̄)
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Band V only (Ī V)
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Both bands II and V (I V)
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Neither band II nor V (Ī V̄)
If the DH pattern for bands II and V shows all four combinations in roughly equal numbers and no strong deviation toward parental combinations, the loci are interpreted as unlinked and assorting independently. In the CSIR NET question, the segregation table for bands II and V shows all four band‑presence/absence combinations without distortion toward any pair, so B is correct.
If the loci had been tightly linked, DH lines would predominantly show either both bands together (parental coupling) or reciprocal absence/presence (repulsion), with very few recombinants.
Statement C: “Band III is uninformative”
A band is uninformative in this context if it cannot be used to trace segregation from P1, P2, or F1, for example when:
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It is present in both parents and in all DH lines (monomorphic band).
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It is absent in both parents and all DH lines.
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It is present in the F1 but also in both parents so that it does not reveal segregation.
In the given question, band III shows polymorphism among DH lines relative to the parents; some lines carry the band and others do not, meaning it segregates and can be mapped or used as a marker locus. Therefore it actually provides genetic information and is not uninformative, making statement C incorrect.
Final evaluation of options
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A only → Incorrect, because B is also correct.
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C only → Incorrect, because C is false.
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A and B only → Correct, since both A (allelic relationship between bands I and IV) and B (independent assortment of bands II and V) are supported by the DH segregation patterns, while C is not.
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A, B and C → Incorrect, because it wrongly accepts C.
Correct answer: Option (3) – A and B only.
