Question

Refer to the following scenario. A cruise ship with 500 people on board crashes on a deserted island. They like the island so much that they decide to stay. There is a small number of people on board with red hair, an autosomal recessive trait. Assume that red hair provides no increase in fitness. 7\. What is most likely to occur with respect to the number of red-haired individuals on the island? (A) There will be no change in the overall number of redhaired people in the population over time. (B) Convergent evolution will occur, with all people eventually becoming red- haired. (C) It is likely that over many generations, the proportion of red-haired people in the population will increase. (D) Red-haired people will probably decrease in the population over many generations.

Short answer

The most likely outcome with respect to the number of red-haired individuals on the island is that there will be no significant change in the overall number of red-haired people in the population over time (Option A). This is because red hair is an autosomal recessive trait with no fitness advantage or disadvantage, and convergent evolution is not relevant in this scenario.

Step-by-step solution

Autosomal Recessive Trait

In this scenario, red hair is described as an autosomal recessive trait, which means an individual must inherit two copies of the recessive gene (one from each parent) in order to express the trait. Therefore, the prevalence of red hair in the population will depend on the frequency of the recessive alleles.

Fitness and Evolution

Fitness refers to how well an organism can reproduce and survive in its environment. In this scenario, it's stated that red hair provides no increase in fitness. As a result, having red hair would not be advantageous or disadvantageous from an evolutionary standpoint.

Convergent Evolution

Convergent evolution refers to the process by which unrelated organisms independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. In this scenario, convergent evolution is not likely to be the cause of an increase in red-haired individuals, as there is no specific advantage of having red hair on the island.

Answering the Question

Based on the above analysis and understanding of genetics and evolution, we can now evaluate the given options: (A) Since red hair provides no increase in fitness, there will be no selective pressure to increase or decrease the number of redhaired people in the population over time. Thus, the frequency of the alleles leading to red hair will remain constant in the population, as long as other factors (i.e., random genetic drift or migration) do not impact the gene pool. (B) Convergent evolution is not relevant here, as there is no advantage to having red hair that would cause other people to eventually become red-haired. (C) The proportion of red-haired people in the population might change over generations due to genetic drift or migration. But since red hair does not provide any increase in fitness, it is unlikely that the proportion would consistently and significantly increase. (D) Red-haired people will not necessarily decrease in the population over many generations, since red hair does not provide any fitness disadvantage. Based on this analysis, we can conclude that Option (A) is the most accurate: There will likely be no significant change in the overall number of red-haired people in the population over time.

Key concepts

Autosomal Recessive Trait

An autosomal recessive trait requires two copies of a recessive allele, one from each parent, for the trait to be expressed. Red hair, as mentioned in the exercise, is an example of such a trait. This model of inheritance means that if individuals with only one copy of the gene (carriers) mate, there's a 25% chance their offspring will express the trait. Carriers do not express the trait because they have one dominant allele masking the recessive one.

• Autosomal recessive traits can remain hidden in the gene pool for generations.
• The prevalence of such traits depends greatly on the initial frequency of the recessive gene and mate choice.
• Individuals with two recessive alleles for a particular trait will express the trait physically.

In a closed population like the island scenario, unless the allele confers some advantage or disadvantage, the proportion of recessive traits would not be expected to change much outside the influence of random genetic drift or new mutations.

Fitness in Biology

In biological terms, fitness refers to an individual's ability to pass on its genes to the next generation. More offspring means greater fitness. Fitness is often confused with strength or health, but in evolutionary biology, it specifically addresses reproductive success.

• Fitness depends on both survival to reproductive age and reproductive success.
• Adaptations that increase fitness are more likely to be passed on and become more common in a population.
• Neutral traits, which neither increase nor decrease fitness, are subject to genetic drift rather than natural selection.

As in the cruise ship scenario, if red hair does not lead to a higher or lower number of offspring, it is considered neutral. This neutral status implies that red hair's frequency in the population may only change due to factors other than natural selection, such as genetic drift.

Convergent Evolution

Convergent evolution occurs when unrelated organisms independently evolve similar traits, usually because they are adapted to similar environments or ecological niches. This process highlights how similar environmental pressures can shape the evolution of species in a comparable manner.

• Examples of convergent evolution include the development of wings in bats and birds, allowing them to fly despite not being closely related.
• Convergent evolution does not imply that all traits within a population will become homogenous.
• It is driven by similar survival challenges rather than shared genetics.

In the context of the red hair trait on the island, there is no environmental pressure favoring red hair, meaning that convergent evolution would not be an applicable concept for predicting the trait's frequency within this population.

Genetic Drift

Genetic drift refers to the random fluctuations in the frequencies of alleles from one generation to the next. These changes are most pronounced in small populations where chance events can have a larger effect on the gene pool.

• Genetic drift can lead to the loss or fixation of alleles over time.
• It is a mechanism of evolution that acts independently of natural selection.
• Bottlenecks and founder effects are examples where genetic drift can have significant impacts on population genetics.

The island scenario is a classic case where genetic drift could come into play. The limited size of the population means random events—like a few high-reproductive red-haired individuals or a disease affecting only non-red-haired individuals—could alter allele frequencies significantly without fitness advantages or disadvantages associated with having red hair.