If an allele is recessive and lethal in homozygotes before they reproduce,
a. The allele will be removed from the population by natural selection in approximately 1,000 years.
b. The allele will likely remain in the population at a low frequency because it cannot be selected against in heterozygotes.
c. The fitness of the homozygous recessive genotype is 0.
d. Both b and c are correct.

Verified step by step guidance

1. Step 1: Understand the problem. The question involves a recessive allele that is lethal in homozygous individuals before reproduction. This means individuals with two copies of the recessive allele (homozygous recessive) do not survive to pass on their genes. The problem asks us to evaluate the fate of this allele in the population and its implications for fitness and natural selection.
2. Step 2: Recall the concept of fitness. Fitness in biology refers to an organism's ability to survive and reproduce. If the homozygous recessive genotype is lethal before reproduction, its fitness is effectively 0 because individuals with this genotype cannot contribute to the next generation.
3. Step 3: Consider the role of heterozygotes. In a population, heterozygous individuals (carrying one dominant and one recessive allele) are not affected by the lethal effects of the recessive allele. This means the recessive allele can persist in the population through heterozygotes, even though homozygous recessive individuals do not survive.
4. Step 4: Analyze the implications for natural selection. Natural selection cannot act directly on the recessive allele in heterozygotes because it does not affect their survival or reproduction. As a result, the allele is likely to remain in the population at a low frequency, rather than being completely eliminated.
5. Step 5: Combine the insights. Based on the above reasoning, the correct answer is likely 'd' because both 'b' (the allele remains at a low frequency) and 'c' (the fitness of the homozygous recessive genotype is 0) are true statements.

Key Concepts

Recessive Alleles

Recessive alleles are variants of a gene that do not manifest their traits in the presence of a dominant allele. For an organism to express a recessive trait, it must inherit two copies of the recessive allele, one from each parent. This concept is crucial for understanding how certain traits are passed on and how they can remain hidden in a population.

Natural Selection

Natural selection is the process through which certain traits become more or less common in a population based on their impact on survival and reproduction. Alleles that confer a survival advantage tend to increase in frequency, while those that are detrimental, such as lethal recessive alleles in homozygotes, are likely to be eliminated over time. This concept helps explain the dynamics of allele frequencies in populations.

Genotype Fitness

Genotype fitness refers to the reproductive success of a particular genotype relative to others in the population. A genotype with a fitness of 0, such as homozygous recessive individuals for a lethal allele, means that these individuals do not survive to reproduce, effectively removing that allele from the gene pool. Understanding fitness is essential for predicting how alleles will behave in a population over generations.