Chapter 23- Evolutionary Processes

Natural selection

________ often favors certain alleles and leads to a decrease in overall genetic variation in a population.

Genetic drift

________ is defined as a change in allele frequencies in a population that is due to chance.

Gene flow

________ occurs when individuals leave one population, join another, and breed.

Heterozygote advantage

________ occurs when heterozygous individuals have higher fitness than homozygous individuals do.

Lateral gene

________ transfer: The transfer of genetic information from one species to another, rather than from parent to offspring.

deleterious alleles

When ________ decline in frequency, purifying selection is said to occur.

error

Sampling ________ occurs when the allele frequencies of a chosen subset of a population (the sample) are different from those in the total population, by chance.

depression

Inbreeding ________ is the decline in average fitness that may take place when homozygosity increases and heterozygosity decreases in a population.

Niαtural selection

________ increases the frequency of certain alleles, the ones that contribute to reproductive success in a particular environment.

Mutαtion modifies

________ allele frequencies by continually introducing new alleles.

Genetic variation

________ is the number and relative frequency of alleles that are present in a particular population.

distinct advantage

Balancing selection occurs when no phenotype has a(n) ________.

Mutation

________ alone is usually inconsequential in changing allele frequencies at a particular gene.

Individuals

________ of the same sex sometimes compete with one another to obtain mates is referred to as intrasexual selection.

genetic bottleneck

A(n) ________ is a sudden reduction in the diversity of alleles in a population.

Hardy Weinberg

________ principle which serves as a mathematical null hypothesis for the study of evolutionary processes.

territory

A(n) ________ is an actively defended area where the owner has exclusive or semi "exclusive use.

intrasexual selection

Both intersexual and ________ help to explain why some aits differ between the sexes of the same species, a difference called sexual dimorphism.

Frequency dependent selection

________ occurs when certain alleles are favored when they are rare, but not when they are common.

Disruptive selection

________ eliminates phenotypes near the average value and favors extreme phenotypes.

Directionαl selection

________ changes the average value of a trait.

Gene flow

________ increases genetic diversity in a recipient population if new alleles arrive with immigrating individuals.

Genetic drift

________ is random with respect to fitness.

Mutations

________ are random with respect to fitness.

Natural selection

________ is the only evolutionary process that results in adaptation, but it is not the only evolutionary process that violates the Hardy- Weinberg assumptions.

Hardy Weinberg

The mathematical model underlying the ________ principle is based on five important assumptions about how populations and alleles behave:

Deleterious alleles

________ are alleles that lower fitness.

Gene flow

________ is the movement of alleles between populations.

Mutation

________ is the ultimate source of genetic variation.

Genetic drift

________ causes allele frequencies to change randomly.

Natural selection

________ occurs in four main patterns, or modes, each affecting genetic variation in different ways:

Genetic drift

________ is most pronounced in small populations.

genetic drift

Over time, ________ can lead to the random loss or fixation of alleles.

Point mutation

A change in a single base pair in DNA

Chromosome-level mutation

A change in the number or composition of chromosomes

Lateral gene transfer

The transfer of genetic information from one species to another, rather than from parent to offspring