Chapter 8 Solutions — Heredity

Trait B is likely to have arisen earlier.

In asexual reproduction, offspring are nearly identical clones of the parent. A new trait arises due to a mutation (an error in DNA copying) in one individual, then spreads through the population as that individual and its descendants reproduce.

Since asexual reproduction produces clones, the only way a trait spreads is through successive generations of reproduction. The longer a trait has been present, the more generations have passed and the higher its frequency in the population.

- Trait B is present in 60% of the population ⇒ it has had more generations to accumulate ⇒ it arose earlier.

- Trait A is present in only 10% of the population ⇒ it has had fewer generations to spread ⇒ it arose more recently.

Therefore, trait B is the older trait that arose earlier in the population.

Variations in a species promote survival by ensuring that at least some individuals can survive when environmental conditions change.

Environmental factors such as temperature, food availability, disease, and predators are not constant. If all individuals in a population were genetically identical, a single drastic change in the environment could wipe out the entire population.

Variations act as insurance for the species. For example:

- If water temperature rises sharply, bacteria that happen to have a heat-resistant variation will survive and reproduce.

- Bacteria without this variation will die out.

- The population as a whole survives because of the pre-existing variation.

Not every variation benefits every individual, but the population benefits because some variants will be suited to the new conditions. The individuals best adapted to the current environment are more likely to survive and pass on their traits to the next generation.

Thus, variations increase the chances that a species will continue to exist even when the environment changes.