SAT Subject Biology Practice Question 156: Answer and Explanation

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Question: 156

6. A horse has 64 chromosomes, while a zebra has 46. In rare cases, it is possible to cause these two species to hybridize, creating offspring that are

A. fertile, with 46 chromosomes
B. fertile, with 55 chromosomes
C. sterile, with 46 chromosomes
D. sterile, with 55 chromosomes
E. sterile, with 64 chromosomes

Correct Answer: D


A hybrid of two species with differing chromosomal numbers will be incapable of forming its own gametes and thus is considered sterile. In order to form a zygote, homologous chromosomes or each gamete must pair. Because zebra gametes will only possess the haploid number of 23 chromosomes and a horse's gamete a haploid number of 32, the resulting zygote will have 54 chromosomes.

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