Chapter 4: Genes and Their Evolution

Which of the following statements about the founder effect is/are correct?

- A founder population's genetic ratios diverge from the parent population's after isolation - A founder population is small, usually less than a few hundred members - The genetic ratios in a founder population are not representative of the parent population

Which of the following must be true in order for a specific allele in a population to remain in a state of equilibrium?

- No mutation, natural selection, or gene flow occur in relation to a specific allele - The population is large - Mating is random

The chemical phenylthiocarbamide (PTC) can be tasted only by certain people. Identify what is correct about PTC and what is incorrect.

- PCT tasters have the dominant allele, T - PTC is similar to a chemical found in bitter-tasting foods

Which of the following can lead to reproductive isolation?

- a mountain range - a large body of water - separated landmasses

Which of the following are examples of hemoglobinopathies (blood diseases related to hemoglobin) that provide a strong selective advantage in areas where malaria is prevalent?

- sickle-cell anemia - thalassemia - glucose-6-phosphate dehydrogenase (G6PD) deficiency

As shown in the maps, sickle cell anemia and malaria have roughly the same distribution in sub-Saharan Africa. Place in chronological order the events that led to this linkage of diseases.

1. The Bantu people migrated South from Cameroon and Nigeria 2. The Bantu cleared large portions of forest in Southern Africa in order to plant crops 3. A dramatic increase in soil erosion occurred and pools of water began to collect 4. People with sickle-cell allele had an adaptive advantage and survived malaria in greater numbers

In regards to sickle-cell anemia, the ____ genotype is beneficial because it allows for resistance to malarial infection without risk of death.

AS The AS genotype means that an individual has one healthy allele (A) and one sickle-cell allele (S). Although two sickle-cell alleles would mean that a person has sickle-cell anemia and is at risk of death, one sickle-cell allele allows a person to be resistant to malarial infection while only having minor complications from the presence of the S allele.

Microevolution

Change in allele frequencies in a population over generations.

All human populations have the same genetic frequencies.

FALSE

Genetic drift occurs more often in exogamous human groups.

FALSE

Populations that are geographically situated next to one another always experience gene flow.

FALSE

The principle used to determine whether an allele is experiencing evolution is called the ___________ law of equilibrium.

Hardy-Weinberg

____________ refers to the changes in allele frequencies that occur from one generation to the next.

Mircoevolution

______________ is the only source of new genetic variation in a population.

Mutation

Huntington's chorea is a genetic abnormality that causes degeneration of parts of the brain that control body movement and abilities such as speech production, triggering involuntary jerky movements of the arms and legs as well as dementia. A person needs only one allele from a parent to have the disease. Why has such a debilitating disease not been removed from the gene pool?

People pass the gene on before they know that they have the disease

point mutation

Replacement of a single nitrogen base with another base, which may or may not affect the animo acid for which the triplet codes

Which of the following are true?

Some gene frequencies remain the same, while others change over time.

Most mutations are due to random changes in the DNA (spontaneous), rather than due to exposure to toxic environmental circumstances (induced).

TRUE

The frequency of alleles does not change from one generation to the next

The population is in equilibrium

The frequency of alleles changes from one generation to the next

The population is not in equilibrium

Gene flow _____________ the genetic variation between two populations

decreases

A ___________ is a local population of organisms that have similar genes, interbreed, and produce offspring.

deme

natural selection

favoring of individuals with characteristics that enhance survival and reproduction

genetic drift

genetic change due to chance

mutation

heritable change in structure or amount of DNA

Macroevolution

large-scale evolutionary changes that take place over long periods of time

transposable element

mobile pieces of DNA that can copy themselves into entirely new areas of chromosomes

In a small population, genetic drift operates over a __________.

relatively short period of time

stabilizing selection

selection against the extremes of the phenotypic distribution, decreasing the genetic diversity for this trait in the population

disruptive selection

selection for both extremes of the phenotypic distribution; may eventually lead to a speciation event

directional selection

selection for one allele over the other alleles, causing the allele frequencies to shift in one direction

frameshift mutation

the change in a gene due to the insertion or deletion of one or more nitrogen bases, which causes the subsequent triplets to be rearranged and the codons to be read incorrectly during translation

What does fitness measure?

the number of offspring that an individual has

gene flow

transfer of genes across population boundaries

Perhaps the best evidence ever documented of natural selection operating on a heritable trait concerns a type of moth, Biston betularia, found in England. Prior to the Industrial Revolution, these moths were ___________.

white peppered with black