Chapter 21 Q/A

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21.1 Q/A

1) Why is genetic variation in a population important?

Genetic variation allows for specialization in an environment, and thus survival OR the elimination of a harmful gene.

2) How do mutations create genetic variability?

Because mutations cause changes in the genome, which then causes genetic variability

3) Are new alleles made through sexual reproduction and independent assortment?

No?

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21.2 Q/A

1) Explain the statement “It is the population, not the individual that evolves.”

Individuals cannot evolve because our DNA doesn't change fast enough, however, small changes passed down from parent to child can accumulate for a change in the population.

2) What is the gene pool of a population? What are genotype, phenotype, and allele frequencies in a population?

The gene pool of a population is the sum of a population's genetic material. Genotype frequencies are how often a certain genotype comes up in a population, Phenotype frequencies are how often a certain phenotypic comes up in a population, and allelic frequencies are how often a certain allele comes up in a population.

3) What are the sources of genetic diversity within the gene pool of a population? What forces promote changes in allele frequencies in the gene pool of a population?

Mutations, nonrandom breeding, predation, the introduction of new alleles, or a small population. These are examples of forces which cause genetic diversity within a gene pool and changes in allelic frequencies.

4) What is the Hardy-Weinberg principle? What is the significance of the Hardy-Weinberg principle in discussions of evolution?

Without any sources of favoritism, there will be no evolution, the frequencies should be equal to the number of organisms with the trait.

5) List the five conditions that must be met for a population to remain in Hardy-Weinberg equilibrium (genetic equilibrium).

1) Random mating of all genotypes

2) No new mutations arise in this population

3) The population is very large (to avoid sampling errors)

4) No migration occurs between this population and another one —no exchange of alleles with other populations

5) No natural selection is occurring at this genetic locus in this population

6) Write the Hardy-Weinberg equation. Understand what the variables in the equation mean.

p + q = 1

p is the frequency of the dominant allele in the population

q is the frequency of the recessive allele in the population. (These are for phenotypes)

p 2 + 2 pq + q 2

(Same as above but for genotype.)

7) Use the equation to calculate allele frequencies when the frequency of homozygous recessive individuals in a population is 25%.

8) In humans, the Rh factor genetic information is inherited from our parents, but it is inherited independently of the ABO blood type alleles. In humans, Rh+ individuals have the Rh antigen on their red blood cells, while Rh− individuals do not. There are two different alleles for the Rh factor known as Rh+ and rh. Assume that a dominant gene Rh produces the Rh+ phenotype, and that the recessive rh allele produces the Rh− phenotype. In a population that is in Hardy-Weinberg equilibrium, if 160 out of 200 individuals are Rh+, calculate the frequencies of both alleles.

Total Dominant: 0.552764045

recessive: 0.4472135955

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21.3 Q/A

1) How do negative assortative mating and positive assortative mating impact genotypic frequencies and heterozygosity?

Positive assortative mating increases homozygosity. Decreases genetic variability.

negative assortative mating increases Heterozygosity Increases genetic variability.

2) How do mutations impact allele frequencies?

They can introduce new alleles which will be used.

3) Which type of population is most likely to be affected by genetic drift?

Small populations.

4) Distinguish between the bottleneck effect and the founder effect. How do they

affect a population?

The Bottleneck Effect

When bottlenecks occur, genetic drift becomes a major evolutionary force. Genetic bottlenecks are rapid and severe declines in the number of individuals in the population, followed by an increase in different allele frequencies. What are some happenings that could cause this process? After the bottleneck, the allelic frequencies in the population may be markedly different than before the decline.

The Founder Effect:

The founder effect occurs when a few “founders” establish a new colony. This type of genetic drift occurs when a small fraction of a population establishes a new colony; this is common in island populations.

The bottleneck effect can significantly reduce the population, either putting it at risk for extinction or forcing the best genes to emerge.

The founder effect will cause the group's unique genes to emerge since the small fraction has been isolated into a new environment.

5) Describe how gene flow can act to reduce genetic differences between adjacent populations.

The two populations will share genetically unique individuals who will bring their population's unique traits to the other and the two will mix, creating a more uniform pocket.

6) A formerly large, random-mating population switches to a high rate of inbreeding. As a consequence, what is likely to happen?

Genetic drift will decrease, homozygosity will increase, and certain genes will crop up more and more often.

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21.4 Q/A

1) There are three modes of natural selection. Distinguish among directional, disruptive, and stabilizing selection. Give an example of each mode of selection.

Stabilizing selection selective force in the environment favors intermediate phenotypes (a classic example is human birth weight) and results in reduced variation in a population.

Directional selection selective force favors one phenotype over another; it favors one extreme of the normal distribution over the other phenotypes. For example, the Galapagos finches are an example of directional selection by diversification into many different species.

Disruptive selection the selective force favors phenotypic extremes and selects for 2 or more different phenotypes. This may result in splitting a population into 2 or more separate species.

2) Describe an example of sexual selection.

Sexual Selection is where certain traits make an individual more desirable as a mate and will, therefore, have more mating opportunities than individuals that do not have these traits. Women wearing high heels is an example of this.

3) Relative to asexual reproduction, sexual reproduction increases genetic diversity within populations through what two mechanisms?

Directional and Stabilizing selection.

4) Light and dark-colored oysters have an advantage over their medium-colored relatives. Light-colored oysters blend into the rocks in the shallows, and the dark oysters blend better into the shadows. The ones in the intermediate range show up against either backdrop, making them easier prey. What kind of selection is this?

Disruptive Selection

5) Why can't natural selection make perfect organisms? (i.e. why can't I have wings to avoid having to deal with traffic?)

Because natural selection doesn't deal with perfection. It only deals with what the species needs. If a species is a land-dwelling ape, it won't evolve wings to fly because there is no reason to invest the time and energy in evolving a complex structure to allow for flying.