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. <span>Identify the chromosome numbers of the parents: a male donkey has 62 chromosomes (2n=62) and a female horse has 64 chromosomes (2n=64).</span>
2. <span>Understand that a mule, being a hybrid of a donkey and a horse, will have a chromosome number that is the sum of half the chromosomes from each parent: (31 from the donkey + 32 from the horse = 63 chromosomes).</span>
3. <span>Recognize that mules are typically sterile because they have an odd number of chromosomes (63), which prevents them from forming balanced gametes during meiosis.</span>
4. <span>Consider the rare event where a female mule gives birth, indicating some form of chromosomal anomaly or fusion that allowed for viable gamete formation.</span>
5. <span>Conclude that the offspring is unlikely to have fully horse-like genetic characteristics because it inherits a mix of chromosomes from both the mule (which has a mix of donkey and horse chromosomes) and the horse, leading to a unique genetic composition.</span>

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. In this case, mules are typically sterile because they have an intermediate number of chromosomes (63) that cannot evenly segregate during reproduction.

Chromosome Number and Compatibility

The chromosome number and compatibility between species play a crucial role in determining the viability of offspring. Horses have 64 chromosomes, while donkeys have 62, leading to mules having 63 chromosomes. This odd number complicates the formation of gametes, making it unlikely for a mule to produce offspring with a complete set of horse-like genetic characteristics, as the genetic material may not align properly during fertilization.

Genetic Recombination and Expression

Genetic recombination is the process by which genetic material is shuffled during meiosis, leading to offspring with a mix of traits from both parents. In the case of a mule mating with a horse, the recombination of genes may not produce a viable combination that resembles a horse due to the differences in chromosome structure and number. As a result, even if an offspring is produced, it is unlikely to exhibit fully horse-like characteristics due to the genetic incompatibility.