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?

Verified step by step guidance

1. Step 1: Understand the chromosome numbers of the parents involved in the mating. A male donkey has 62 chromosomes (2n=62), and a female horse has 64 chromosomes (2n=64). Mules are hybrids formed by combining half the chromosomes from each parent.
2. Step 2: Determine the chromosome number of the mule. Since mules inherit half of their chromosomes from the donkey and half from the horse, the mule will have (62/2) + (64/2) chromosomes. Use this formula to calculate the mule's chromosome count.
3. Step 3: Consider the offspring of the mule and horse mating. The mule contributes half of its chromosomes to the offspring, and the horse contributes half of its chromosomes. Use the mule's chromosome count from Step 2 and the horse's chromosome count (64) to calculate the offspring's chromosome number.
4. Step 4: Add the contributions from the mule and the horse to determine the total chromosome count of the offspring. This involves summing half of the mule's chromosomes and half of the horse's chromosomes.
5. Step 5: Verify the result conceptually. Since mules are typically sterile due to uneven chromosome pairing, this rare event suggests that the mule's reproductive cells were able to contribute a viable set of chromosomes. Ensure the calculated chromosome number aligns with the expected hybridization pattern.

Key Concepts

Chromosome Number in Species

Different species have distinct chromosome numbers, which are crucial for understanding hybridization. In this case, donkeys have 62 chromosomes (2n=62) and horses have 64 chromosomes (2n=64). When these two species mate, their offspring, mules, inherit a mix of chromosomes but typically have an intermediate number, resulting in 63 chromosomes (2n=63), making them sterile due to uneven chromosome pairing during meiosis.

Hybrid Sterility

Hybrid sterility occurs when the offspring of two different species are unable to reproduce. Mules, the offspring of a male donkey and a female horse, are a classic example of this phenomenon. They possess an odd number of chromosomes (63), which complicates meiosis, preventing the formation of viable gametes. However, rare instances, like the one described, can lead to unexpected reproductive outcomes.

Chromosome Contribution in Hybrid Offspring

In the case of a mule mating with a horse, the chromosome contribution from each parent is essential to determine the offspring's chromosome number. The mule has 63 chromosomes, while the horse contributes 64. Therefore, the mule-horse offspring would inherit a total of 63 (from the mule) + 64 (from the horse) = 127 chromosomes, which is an unusual scenario but illustrates the complexities of hybrid genetics.