Bio Ch. 23

What are the five conditions that must be met for the Hardy-Weinberg theorem to be valid?

(1) The population is very large. (The effect of chance on changes in allele frequencies is greatly reduced.) (2) Matings are random. (Individuals show no mating preference for a particular phenotype.) (3) There are no net changes in the gene pool due to mutation. (Mutation from A to a equals mutation from a to A.) (4) There is no migration of individuals into and out of the population, i.e. no gene flow (transfer of alleles between populations). (5) There is no natural selection; all genotypes are equal in reproductive success

Population

A population is a localized group of individuals capable of interbreeding and producing fertile* offspring.

What is meant by the term "heterozygote advantage"?

Some individuals who are heterozygous at a particular locus have greater fitness than homozygotes. Natural selection will tend to maintain two or more alleles at that locus. The sickle-cell allele causes mutations in hemoglobin but also confers malaria resistance. It exemplifies the heterozygote advantage.

What are the two processes that contribute to genetic variation and make evolution possible? Which is of greater importance for producing genetic differences?

1. mutations 2. sexual reproduction sexual reproduction is far more important that mutation bc of 1. crossing over 2. independent assortment 3. fertilization their comined effect ensure that sexual reproduction arranges existing alleles into new conbinations each generation

What three major factors alter allele frequencies and bring about most evolutionary change?

1. Natural selection 2. Genetic Drift 3. Gene Flow

Why is natural selection unable to fashion perfect organisms?

1. Selection can only edit existing variations. 2. Evolution is limited by historical constraints. 3. Adaptations are often compromises. 4. Chance, natural selection and the environment interact. Natural selection operates on a "better than" basis. The evidence for evolution can be seen in the many imperfections of the organisms it produces.

What comprises a gene pool?

A gene pool consists of all gene loci in all individuals of the population The gene pool is the total aggregate of genes in a population at any one time

Be able to explain how diploidy and balancing selection help to preserve genetic variation within a population.

Diploidy maintains genetic variation in the form of hidden recessive alleles Balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population - balancing selection leads to a state called balanced polymorphism Why isn't the bad allele just removed from the environment? bc of diploidy

Be able to distinguish among the three modes of selection: directional, disruptive and stabilizing.

Directional selection favors individuals at one end of the phenotypic range. Disruptive selection favors individuals at both extremes of the phenotypic range. Stabilizing selection favors intermediate variants and acts against extreme phenotypes.

Gene Flow

Gene flow consists of genetic additions or subtractions from a population, resulting from movement of fertile individuals or gametes. Gene flow causes a population to gain or lose alleles. It tends to reduce differences between populations over time.

What is meant by the term "frequency-dependent selection"?

In frequency-dependent selection, the fitness of any morph declines if it becomes too common in the population.

Be able to distinguish between the terms "intra" and "intersexual" selection.

Intrasexual selection is competition among individuals of one sex for mates of the opposite sex. Intersexual selection occurs when individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex. Selection may depend on the showiness of the male's appearance.

What is microevolution? What is the smallest unit of evolution?

Microevolution is the change in the genetic makeup (allele frequencies) of a population over time.

Neutral Variation

Neutral variation is genetic variation that appears to confer no selective advantage. For example, most of the DNA base differences between humans are found in untranslated parts of the genome that appear to confer no selective advantage.

Know and be able to apply the Hardy Weinberg equation: p2 +2pq + q2 = 1.

P + Q = 1 (frequency of alleles) p^2 +2pq + q^2 = 1 (frequency of genotype)

What is population genetics?

Population genetics is the study of the distribution and change in frequency of alleles within populations

What is the Hardy-Weinberg Theorem? What does it state?

The Hardy-Weinberg principle describes a population that is not evolving. It states that frequencies of alleles and genotypes in a population's gene pool remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work. Mendelian inheritance preserves genetic variation in a population. Such a gene pool is said to be in Hardy-Weinberg Equilibrium.

What is the bottle neck effect? founder effect?

The bottleneck effect is a sudden reduction in population size due to a change in the environment. The resulting gene pool may no longer be reflective of the original population's gene pool. Understanding the bottleneck effect can increase understanding of how human activity affects other species. The founder effect occurs when a few individuals become isolated from a larger population. Allele frequencies in the small founder population can be different from those in the larger parent population.

Gene Pool

The gene pool is the total aggregate of genes in a population at any one time. The gene pool consists of all gene loci in all individuals of the population.

What is meant by the term "relative fitness"?

The phrases "struggle for existence" and "survival of the fittest" are commonly used to describe natural selection but can be misleading. Reproductive success is generally more subtle and depends on many factors. Fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals. Relative fitness is the contribution of a genotype to the next generation, compared with contributions of alternative genotypes for the same locus.

Genetic Drift

The smaller a sample, the greater the chance of deviation from a predicted result. Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next. Genetic drift tends to reduce genetic variation through losses of alleles. Effects of Genetic Drift: A Summary 1. Genetic drift is significant in small populations 2. Genetic drift causes allele frequencies to change at random 3. Genetic drift can lead to a loss of genetic variation within populations 4. Genetic drift can cause harmful alleles to become fixed