Question

Population geneticists study changes in the nature and amount of genetic variation in populations, the distribution of different genotypes, and how forces such as selection and drift act on genetic variation to bring about evolutionary change in populations and the formation of new species. From the explanation given in the chapter, what answers would you propose to the following fundamental questions? (a) How do we know how much genetic variation is in a population? (b) How do geneticists detect the presence of genetic variation as different alleles in a population? (c) How do we know whether the genetic structure of a population is static or dynamic? (d) How do we know when populations have diverged to the point that they form two different species? (e) How do we know the age of the last common ancestor shared by two species?

Short answer

Answer: Geneticists calculate the heterozygosity and the allelic diversity of the population to determine the amount of genetic variation. Question: How do geneticists detect the presence of genetic variation as different alleles in a population? Answer: Genetic variation is detected through techniques such as DNA sequencing, PCR amplification, and gel electrophoresis, which help identify variations like SNPs and indels. Question: How do we know whether the genetic structure of a population is static or dynamic? Answer: By studying changes in allele frequencies through time, geneticists can determine if the population's genetic structure is static (constant allele frequencies) or dynamic (significant changes in allele frequencies). Question: How do we know when populations have diverged to the point that they form two different species? Answer: Reproductive isolation and genetic divergence are studied, with distinct species formation indicated by the inability to produce viable, fertile offspring and a greater degree of genetic divergence. Question: How do we know the age of the last common ancestor shared by two species? Answer: The age of the last common ancestor can be estimated using molecular clock methods, by measuring genetic divergence and assuming a constant rate of genetic change. Fossil evidence and geological information are also used to corroborate these estimates.

Step-by-step solution

a) Measuring genetic variation in a population

To determine the amount of genetic variation in a population, geneticists calculate the heterozygosity and the allelic diversity of the population. Heterozygosity is the proportion of heterozygous individuals (having different alleles of a gene) in the population, while allelic diversity is the number of different alleles present for a particular gene. Geneticists analyze multiple genes in order to have an accurate estimation of overall genetic variation in the population.

b) Detection of genetic variation as different alleles

Genetic variation can be detected through various techniques, including DNA sequencing, polymerase chain reaction (PCR) amplification, and gel electrophoresis. These techniques enable geneticists to compare the DNA of different individuals within a population and identify genetic variations, such as single nucleotide polymorphisms (SNPs) and insertion-deletion events (indels), that represent different alleles.

c) Determining if a population's genetic structure is static or dynamic

To determine whether the genetic structure of a population is static or dynamic, geneticists study changes in allele frequencies through time. They collect and compare genetic information from individuals across generations and analyze the changes in allele frequency patterns. If there are significant changes in allele frequencies, the population's genetic structure would be considered dynamic, whereas if the allele frequencies remain constant, the population's genetic structure would be considered static.

d) Identifying the divergence of populations into different species

Determining when populations have diverged to the point of forming distinct species typically involves studying reproductive isolation and genetic divergence. Reproductive isolation occurs when two populations can no longer produce viable, fertile offspring, resulting in the formation of distinct species. Genetic divergence can be quantified by comparing DNA sequences between the populations, with a greater degree of divergence indicating a greater likelihood of speciation.

e) Estimating the age of the last common ancestor shared by two species

The age of the last common ancestor shared by two species can be estimated using molecular clock methods. This involves comparing and measuring the genetic divergence between the species and assuming a constant rate of genetic change over time. Applying this rate of change to the observed genetic differences, geneticists calculate the time elapsed since the last common ancestor shared by the two species. Additionally, they use fossil evidence and geological information to corroborate these estimates.