21. A cruciform structure of chromosome during meiosis is a characteristic feature of:
(1) Translocation (2) Inversion
(3) Deletion (4) Duplication
Detailed explanation of options:
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Translocation – correct
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In a reciprocal translocation, segments are exchanged between two non-homologous chromosomes.
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In a heterozygote, there are two normal and two translocated chromosomes. During prophase I, homologous regions of all four try to pair, forming a cross-shaped “cruciform” or quadrivalent structure.
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This cruciform configuration is diagnostic of reciprocal translocation in meiosis.
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Inversion
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Inversion flips a segment within a single chromosome.
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In an inversion heterozygote, pairing of the normal and inverted homolog produces an “inversion loop,” not a cruciform cross.
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Only two homologous chromosomes are involved, so it does not make a four-armed cross.
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Deletion
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A deletion removes a segment from one homolog.
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During pairing, the normal homolog forms a single unpaired loop to match the shortened partner; again, this is a loop, not a cruciform with four arms.
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Duplication
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A duplication repeats a segment on one homolog.
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During pairing with the normal homolog, the extra segment often loops out on the duplicated chromosome.
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This also produces a loop configuration, not a cross.
Therefore, a cruciform (cross-shaped) chromosome structure during meiosis is a characteristic feature of a reciprocal translocation, so option (1) Translocation is correct.
