Biology: Evolution & Ecology

What are the three primary observations Darwin used to infer the process of natural selection?

1. Individuals in a population vary in heritable traits. 2. A population can produce more offspring than can survive. 3. Species are generally adapted to their environments.

Contrast disruptive selection with stabilizing selection regarding their effects on phenotypic variance.

Disruptive selection favors individuals at both extremes of the phenotypic range, increasing variance, while stabilizing selection favors intermediate variants and reduces variance by acting against extremes.

Explain the bottleneck effect and its primary consequence on a population's gene pool.

The bottleneck effect occurs when a sudden environmental change drastically reduces population size. The resulting gene pool may no longer reflect the original population's genetic diversity, often leading to reduced variation.

Define gene flow and describe its typical effect on the genetic divergence between two neighboring populations.

Gene flow is the transfer of alleles into or out of a population due to the movement of fertile individuals or gametes. It tends to reduce genetic differences between populations over time.

Why is mutation considered the ultimate source of all genetic variation in a population?

Mutation is the only mechanism that creates entirely new alleles; other mechanisms like crossing over or independent assortment only reshuffle existing alleles.

In a population in Hardy-Weinberg equilibrium, if the frequency of a recessive allele (q) is 0.3, what is the frequency of the heterozygous genotype?

The frequency is 0.42. Using p + q = 1, p = 0.7. The frequency of heterozygotes is 2pq, so 2(0.7)(0.3) = 0.42.

Distinguish between allopatric and sympatric speciation mechanisms.

Allopatric speciation occurs when populations are geographically isolated, preventing gene flow. Sympatric speciation occurs in populations that live in the same geographic area, often through polyploidy or habitat differentiation.

What are homologous structures, and what do they reveal about the evolutionary history of different species?

Homologous structures are anatomical resemblances in different species that represent variations on a structural theme present in a common ancestor, indicating shared evolutionary descent.

How does molecular biology, specifically DNA sequencing, provide evidence for the 'Tree of Life'?

Molecular biology shows that all organisms share the same genetic code. The degree of similarity in DNA sequences between species correlates with how recently they shared a common ancestor.

Describe the difference between the exponential and logistic growth models in population ecology.

Exponential growth (dN/dt = rN) occurs under ideal conditions with unlimited resources, resulting in a J-shaped curve. Logistic growth (dN/dt = rN[(K-N)/K]) slows as the population approaches the carrying capacity (K), resulting in an S-shaped curve.