Question

Hybrid breakdown occurs when interspecies hybrids a do not develop past the early embryonic stages. b have a reduced life span. c are infertile. d are fertile but produce offspring with reduced viability and fertility. e produce offspring that express the traits of only one of the original species.

Short answer

The correct answer is 'd'. Hybrid breakdown occurs when the interspecies hybrids are fertile but their offspring have reduced viability and fertility.

Step-by-step solution

Understand key definitions

First, one must understand what 'hybrid breakdown' means. It refers to the situation where interspecies hybrids are less fit than their parents. This can manifest in different ways.

Evaluate each option individually

Now, let's evaluate each of the presented options to determine which one correctly describes hybrid breakdown.

Select the correct option

The correct answer, in this case, is 'd'. Hybrids could potentially be fertile but they produce offspring that have reduced viability and fertility, indicating they are less 'fit' than their parents, which exactly qualifies as hybrid breakdown.

Key concepts

Interspecies Hybrids

Interspecies hybrids are offspring resulting from the mating of parents from two different species. These hybrids inherit genetic material from both parent species. Because of this, hybrids can sometimes have unique combinations of traits.

However, despite their unique qualities, hybrids often face challenges in survival or reproduction. In the wild, hybridization can occur naturally, like with the mule, a cross between a donkey and a horse.

• Hybrids are fascinating because they can blend characteristics not found in either parent species alone.
• However, their creation can lead to complications, such as genetic incompatibilities, affecting their overall viability and fertility.

Fertility

Fertility in hybrids refers to their ability to reproduce successfully. In interspecies hybrids, fertility can vary greatly. Some hybrids, like the mule, are almost universally infertile and cannot produce offspring.

Others may be fertile themselves, but if they reproduce, their offspring could exhibit signs of reduced fertility.

• Fertility is often compromised in hybrids due to genetic differences between the parent species.
• Despite being fertile, hybrids can produce offspring with diminished reproductive capabilities.

The level of fertility can also serve as an indicator of how closely related the parent species are, genetically.

Viability

Viability pertains to the ability of the hybrid offspring to survive and thrive. It's a crucial aspect that affects whether the hybrid can live a healthy and fulfilling life.

Hybrids might initially appear strong, but issues can arise in their offspring. This reduced viability often includes shorter lifespans or increased susceptibility to disease.

• Reduced viability can lead to hybrid breakdown, where subsequent generations become weaker or less healthy.
• The environment can also affect a hybrid's viability, influencing its ability to adapt and survive.

In many cases, hybrids' initial apparent viability may mask underlying genetic issues that only become prominent in their progeny.

Genetic Incompatibility

Genetic incompatibility occurs when the genetic makeup of hybrid individuals leads to complications. This is due to differences in parental genes, which might not work well together.

As a result, incompatible genes can manifest in the form of reduced fertility or viability in hybrid offspring.

• Genetic incompatibility is a significant challenge facing interspecies hybrids.
• These incompatibilities can result in a range of negative outcomes, such as developmental issues or health problems.

It is this genetic incompatibility that often leads to hybrid breakdown, as these underlying issues get magnified over generations, reducing the success rate of hybrid offspring.