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.
Why is it very unlikely that the offspring will have fully horse-like genetic characteristics?

Verified step by step guidance

1. Understand the chromosomal differences between the donkey and horse: A male donkey has 62 chromosomes (2n=62), while a female horse has 64 chromosomes (2n=64). When they mate, the mule inherits one set of chromosomes from each parent, resulting in a hybrid with 63 chromosomes (not an even number).
2. Recognize why mules are sterile: The odd number of chromosomes (63) prevents proper pairing during meiosis, which is necessary for the production of viable gametes. This sterility is a key reason why mules cannot typically reproduce.
3. Consider the rare event of a female mule giving birth: In this case, the mule must have produced a viable egg. This could occur if the mule's chromosomes underwent an unusual event, such as nondisjunction or partial pairing, allowing the formation of a functional gamete.
4. Analyze the genetic contribution to the offspring: The mule's gamete would contain a mix of donkey and horse chromosomes. When this gamete combines with the horse's sperm (which contains only horse chromosomes), the offspring would inherit a combination of donkey and horse genetic material, making it unlikely to be fully horse-like.
5. Conclude why the offspring is unlikely to be genetically fully horse-like: The mule's gamete introduces genetic material from both donkey and horse origins. This hybridization ensures that the offspring will have a mix of genetic characteristics, rather than being purely horse-like.

Key Concepts

Hybrid Sterility

Hybrid sterility occurs when the offspring of two different species, such as a mule (a cross between a horse and a donkey), are unable to reproduce. This is often due to differences in chromosome number and structure, which can lead to improper pairing during meiosis, resulting in gametes that are not viable.

Chromosome Number and Compatibility

The male donkey has 62 chromosomes, while the female horse has 64, leading to mules having an intermediate chromosome number of 63. This odd number of chromosomes complicates meiosis, making it difficult for mules to produce gametes that can successfully combine with those of a horse, thus limiting the genetic diversity and compatibility of any potential offspring.

Genetic Recombination

Genetic recombination is the process by which genetic material is exchanged between chromosomes during meiosis. In the case of a mule mating with a horse, the uneven chromosome numbers hinder effective recombination, making it unlikely for the offspring to inherit a complete set of horse-like genetic traits, as the genetic material may not align properly during gamete formation.