Biology Chapter 21 Review

3 sources of new gene combinations

1. Crossing over 2. Independent assortment 3. Fertilization

2 sources of genetic variation

1. Mutation 2. Gene duplication

3 mechanisms for changing allele frequency

1. Natural selection 2. Genetic drift 3. Gene flow

5 parts of the Hardy-Weinberg principle that characterize a non-evolving population

1. No mutations 2. Randome mating 3. No natural selection 4. Extremely large population size 5. No gene flow

4 reasons why natural selection cannot fashion perfect organisms

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

4 main effects of genetic drift

1. is significant in small populations 2. can cause allele frequencies to change at random 3. can lead to a loss of genetic variation within populations 4. can cause harmful alleles to become fixed

There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in population 2, all with genotype AA. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is most likely an example of A) genetic drift. B) gene flow. C) disruptive selection. D) nonrandom mating.

A) genetic drift.

If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus? A) gene variability = 0%; number of alleles = 0 B) gene variability = 0%; number of alleles = 1 C) gene variability = 0%; number of alleles = 2 D) gene variability > 0%; number of alleles = 2

B) gene variability = 0%; number of alleles = 1

No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is A) new mutations that occurred in the preceding generation. B) genetic drift due to the small size of the population. C) the reshuffling of alleles in sexual reproduction. D) geographic variation within the population. E) environmental effects.

C) the reshuffling of alleles in sexual reproduction.

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2? A) 0.7 B) 0.49 C) 0.21 D) 0.42

D) 0.42

Natural Selection changes allele frequencies because some ____________ survive and reproduce more successfully than others. A) alleles B) loci C) gene pools D) Individuals

D) Individuals

Sparrows with average-sized wings survive severe storms better than those with longer or shorter wings, illustrating A) the bottleneck effect. B) disruptive selection. C) frequency-dependent selection. D) stabilizing selection.

D) stabilizing selection.

Advantage of heterozygote (with example)

It is when heterozygotes have a higher fitness than homozygotes. Ex. Sickle cell allele causes deleterious mutations in hemoglobin as homozygous recessive but it also confers malaria resistance. So being heterozygous gives one the protection from malaria while not giving the harmful effects of mutations to hemoglobin

Disruptive Selection

favors individuals at both extremes of phenotypic range

Directional Selection

favors individuals at one end of phenotypic range

Stabilizing Selection

favors intermediate variants and acts against extremes