Microevolution II

Question 1

What is a bottleneck?

Answer 1

A severe reduction in population size; there is a restricted group of individuals that contribute to the remaining genetic diversity.

Question 2

What causes a bottleneck effect?

Answer 2

This occurs when there is a drastic reduction in population size due to a sudden change in the environment. The resulting gene pool may no longer be reflective of the original population’s gene pool.

Question 3

If the population remains small after a bottleneck effect, what other effect affects its genetic diversity?

Answer 3

Genetic drift (only in small populations).

Question 4

What is the relationship between population size and genetic drift?

Answer 4

The smaller the sample size, the greater the chance that a random deviation from predictive results such as genetic drift can occur.

Question 5

When does the founder effect occur?

Answer 5

The founder effect occurs when a few individuals become isolated from a larger population. The allele frequencies in the smaller population are different from those in the parent population.

Question 6

What two processes produce the variation in gene pools that contributes to the differences among individuals?

Answer 6

1. Mutation
2. Sexual recombination

Question 7

What are mutations?

Answer 7

Mutations are changes in the nucleotide sequence of DNA and can involve changes of one (point mutations) or many nucleotides. Mutations cause new genes and alleles to arise.

Question 8

What are synonymous mutations?

Answer 8

Mutations that don’t change the encoded amino acid.

Question 9

What are nonsynonymous mutations?

Answer 9

Changes in nucleotides that change amino acids.

Question 10

Which types of mutations are typically harmful or deleterious?

Answer 10

Chromosomal mutations that delete, disrupt, or rearrange many loci.

Question 11

Why do males contribute more harmful mutations than females to their offspring?

Answer 11

In humans, the rate of point mutations is 5 times higher in sperm than eggs, so fathers contribute most harmful mutations.

Question 12

Where is mutation common and where is it rare?

Answer 12

Mutation is common on a per gamete (or per genome) basis but rare per gene.

Question 13

What characteristics describe most mutations?

Answer 13

Most mutations with phenotypic effects are deleterious and recessive.

Question 14

What are the two principle ways to not have random mating?

Answer 14

1. Assortative mating
2. Inbreeding

Question 15

What is assortative mating?

Answer 15

Like genotypes mate with each other, or avoid each other.

Question 16

What is inbreeding?

Answer 16

Mating among individuals that are more closely related than those drawn by chance from the population.

Question 17

What effect does positive assortative mating have?

Answer 17

It decreases heterozygosity for the gene(s) affecting the trait. On average, heterozygotes decrease if similar genotypes are pairing, but only for the loci affecting the trait.

Question 18

How does the number of heterozygotes change after each generation with complete positive assortative mating?

Answer 18

The number decreases by half.

Question 19

What effect does negative assortative mating have?

Answer 19

It increases heterozygosity for the gene(s) affecting that trait. On average, heterozygotes increase if dissimilar genotypes are pairing.

Question 20

What is the effect of inbreeding?

Answer 20

It changes genotype frequencies by increasing the proportion of homozygotes and reducing the proportion of heterozygotes across the entire genome. It the most extreme case (selfing), it has effects just like positive assortative mating, but across the whole genome.

Question 21

The genotype changes caused by assortative mating affect only which loci?

Answer 21

Those contributing to the phenotype.

Question 22

The genotype changes caused by inbreeding affect which loci?

Answer 22

All of the loci in the genome.

Question 23

Why can the results of inbreeding and assortative mating be reversed with one generation of random mating?

Answer 23

They only affect genotype frequencies (not allele ones) so their effects may be quite ephemeral (lasting for a short time).

Question 24

Why does inbreeding reduce fitness?

Answer 24

It generates offspring homozygous for deleterious alleles (inbreeding depression).

Question 25

What is genetic drift?

Answer 25

One of the basic mechanisms of evolution, it is the evolutionary equivalent of a sampling error.

Question 26

How does gene flow affect allele frequencies?

Answer 26

It can change them quite dramatically. Within a population, it can introduce or reintroduce alleles, increasing its genetic variation. By moving genes around, it can make distant populations genetically similar to one another, hence reducing the chance of divergence. In short, gene flow tends to reduce variation among populations over time.