Chapter 23

Random mutating

If individuals tend to mate within a subset of the population, such as their nearneighbors or close relatives (inbreeding), random mixing of gametes does not occur, and genotype

No gene flow

By moving alleles into or out of populations, gene flow can alter allele frequencies.

No natural

Differences in the survival and reproductive success of individuals carrying differentgenotypes can alter allele frequencies.

founder effect

Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.

bottleneck effect

Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.

What is microevolution?

Microevolution is evolutionary change below the species level; change in the allele frequencies in apopulation over generations.

What is the ultimate source of new alleles?

Mutation

What is the only mechanism that is adaptive, or improves the match between organisms and theirenvironment?

Natural selection

Which of the factors results in a random, nonadaptive change in allelic frequencies?

Natural selection is the only mechanism that consistently causes adaptive evolution.

In evolutionary terms, fitness refers only to the ability to leave offspring and contribute to the gene pool of the next generation. It may have nothing to do with being big, or strong, or aggressive. Define relative fitness.

Relative fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population.

How many mutations occurred in the exon areas? How many of these mutations altered the amino acid sequence of the protein?

Seventeen occurred in exon areas. Of these, only one substitution altered the amino acid sequence.

What is often the result of sexual selection?

Sexual dimorphism: A difference between the two sexes in secondary sexual characteristics. Balancing selection: Natural selection that maintains two or more phenotypic forms in a population.

Stabilizing: Directional: Disruptive:

Stabilizing: Removes extreme variants from the population and preserves intermediate types Directional: Shifts the overall makeup of the population by favoring variants that are at one extreme of the distribution Disruptive: Favors variants at both ends of the distribution

No mutation

The gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated.

Extremely large population size

The smaller the population, the more likely it is that allele frequencies will fluctuate bychance from one generation to the next (a process called genetic drift).

The Hardy-Weinberg principle is used to describe a population that is not evolving. What does this principle state?

This principle states that frequencies of alleles and genotypes in a population remain constant fromgeneration to generation, provided that only Mendelian segregation and recombination of alleles are at work.

What is the relative fitness of a sterile mule?

Zero

Which of the factors above tends to reduce the genetic differences between populations and make populations more similar?

gene flow

Of the three factors you previously listed, only one results in individuals that are better suited to their environment. Which is it?

natural selection

Natural selection: Genetic drift: Gene flow:

natural selection: Natural selection results in alleles being passed to the next generation in proportions that differ from those in the present generation. genetic drift: The process in which chance events cause allelic frequencies to fluctuate unpredictably from one generation to the next gene flow: The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes

Give four reasons why natural selection cannot produce perfect organisms.

1. Selection can act only on existing variations. 2. Evolution is limited by historical constraints. 3. Adaptations are often compromises. 4. Change, natural selection, and the environment interact.

How many total mutations are shown in the alcohol dehydrogenase gene?

43 substitutions + 5 insertions + 1 26bp deletion = 49 mutations

Chromosomal changes that delete, disrupt, or rearrange many loci at once are usually harmful. How does gene duplication occur? How might it play a role in evolution?

Gene duplication can occur due to errors in meiosis, slippage during DNA replication, or the activities of transposable elements. Duplications that do not have severe effects can persist over generations,allowing mutations to accumulate. The result is an expanded genome with new genes that may take on new functions, playing a major role in evolution.

What are the three main mechanisms that can cause changes in allele frequency?

Natural selection, genetic drift, and gene flow

Much of the genetic variation that makes evolution possible comes through sexual reproduction. What are the three mechanisms by which sexual reproduction shuffles existing alleles?

1. Crossing over 2. Independent assortment of chromosomes 3. Fertilization

What is a gene pool?

A gene pool consists of all copies of every type of allele at every locus in all members of the population.

Mutations are any change in the nucleotide sequence of an organism's DNA. These mutations providethe raw material from which new traits may arise and be selected. What occurs in a point mutation? Do point mutations always result in a change of phenotype?

A point mutation reflects a change in one base in a gene. Not all point mutations result in a change of phenotype because so much of the DNA in eukaryotic genomes does not code for protein products andbecause of the redundancy in the genetic code.

What is a population?

A population is a group of individuals of the same species that live in the same area and interbreed,producing fertile offspring.

Explain how a substitution error in an exon could have no effect on the amino acid sequence.

A substitution error will not cause a change in the reading frame, and, due to the redundancy in thegenetic code, substitutions in the third base of the codon often code for the same amino acid.

The greater the number of fixed alleles, the lower the species' diversity. What does it mean to say that an allele is fixed?

An allele is said to be fixed if only one allele exists for a particular locus in a population.