Mating between a male donkey (2n=62) and a female horse (2n=64) produces sterile mules. Recently, however, a very rare event occurred—a female mule gave birth to an offspring by mating with a horse.

How many chromosomes does the mule–horse offspring carry?

Key Concepts

Chromosome Number in Species

Different species have distinct chromosome numbers, which are crucial for understanding hybridization. In this case, the male donkey has 62 chromosomes, while the female horse has 64. The resulting mule, a hybrid, typically has an intermediate chromosome count of 63, but is usually sterile due to the mismatch in chromosome numbers.

Hybrid Sterility

Hybrid sterility occurs when the offspring of two different species are unable to reproduce. Mules, resulting from the mating of a donkey and a horse, are generally sterile because their uneven chromosome count prevents proper gamete formation. However, rare exceptions, like the female mule in this scenario, can occur, leading to potential reproduction.

Chromosome Contribution in Offspring

When two organisms mate, the offspring inherit a combination of chromosomes from both parents. In this case, if the female mule (63 chromosomes) mates with a horse (64 chromosomes), the offspring could inherit a mix of these chromosomes. The possible chromosome counts for the mule-horse offspring could be 63 or 64, depending on the gametes contributed by the mule.