23. Chromosome number can evolve by smaller-scale changes than duplication of en

Question

23. Chromosome number can evolve by smaller-scale changes than duplication of entire chromosome sets. For example, domestic horses have 64 chromosomes per diploid set while Przewalski's horse, an Asian subspecies has 66. Przewalski's horse is thought to have evolved from an ancestor with 2n = 64 chromosomes. The question is, where did its extra chromosome pair originate? (A) Generate a hypothesis explaining the origin of the new chromosome in Przewalski's horse, examine the adjacent figure. This drawing shows how certain chromosomes synapse in the hybrid offspring of a domestic horse-Przewalski's horse mating. The remaining chromosomes show a normal 1:1 pairing. (B) Do you think this change in chromosome number involved a change in the number of genes or alleles present? Explain your answer.

Explanation / Answer

1) .The addition of one or more set of chromosomes,identical to the normal haploid complements of the same specieces,results in aneuploidy.It occurs due to the non disjunction during the meiosis.Here shown is tetrasomy condition(2n+2).

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