A horse has 2n = 64 and a donkey has 2n = 62. The hybrid of these two species, the mule, has 63 chromosomes and is sterile. Why are mules sterile?
A) Their zygotes cannot complete the first mitotic division to form the two-cell stage.
B) They cannot physically mate with each other.
C) They cannot physically mate with horses and donkeys.
D) They lack homologous chromosomes and cannot undergo meiosis.

Question

Quizplus · Accepted Answer

Mules are sterile because they have an odd number of chromosomes (63), which means they lack homologous pairs for each chromosome. This prevents them from undergoing normal meiosis, as homologous chromosomes cannot pair up and segregate properly during meiosis I, leading to gametes with an incorrect number of chromosomes.

A Horse Has 2n = 64 and a Donkey Has