Biology 1B - Evolution RSAQ's

Uniformitarianism is an important assumption in historical science because:

without the uniformitarian assumption, scientists cannot determine what processes caused past events

Evolutionary biology can be used to… 

Inform practices that will decrease the development of antibiotic-resistant strains of bacteria.

 

Explain why the organisms we see are adapted to the environments they live in.

 

Help us understand the origins of novel viral pathogens.

Which is NOT a key idea in the theory of natural selection?

There are just enough resources for each generation of organisms.

In the Origin of Species, what was the point of Darwin’s discussion of the rudimentary legs of some snakes?

They indicate descent from a species with fully developed legs.

Which one of the following statements best describes the importance of homologous structures for Darwin’s argument?

Homologous structures indicate shared ancestry.

How did Darwin address the question of why transitional forms are rare?

Darwin claimed that transitional forms are not usually seen because, as the species continues to change, eventually there will not be living representatives of the transitional form.

Which observation did Darwin NOT attribute to shared ancestry among species?

When organisms are very different in adulthood, they don't share any similarities in their developmental process.

Which statement best describes the neo-Darwinian synthesis?

Evolution is caused by changes in allele frequencies within species.

The neo-Darwinian synthesis combines Darwin's theory of natural selection with Mendelian genetics, emphasizing that evolution is driven by genetic variation and inheritance.

Which of the following population samples is closest to the Hardy-Weinberg frequencies?

a. AA: 600, Aa: 300, aa: 100.

b. AA: 500, Aa: 500, aa: 500.

c. AA: 700, Aa: 200, aa: 100.

d. AA: 340, Aa: 320, aa: 340.

e. AA: 640, Aa: 320, aa: 40.

e. AA: 640, Aa: 320, aa: 40.

The observed frequencies (AA = 0.64, Aa = 0.32, aa = 0.04) equal the expected HW frequencies (AA = 0.80 x 0.80 = 0.64, Aa = 2 x 0.80 x 0.20 = 0.32, aa = 0.20 x 0.20 = 0.04).

If one individual in 1,000,000 has a genetic disease caused by a recessive Mendelian allele, roughly what fraction of individuals in a randomly mating population are heterozygous carriers of this disease allele?

2/1,000

If the frequencies of the three genotypes in a population, AA, Aa, and aa are 0.5, 0.2, and 0.3 (in order), the frequency of the A allele is:

0.6

List three conditions required for natural selection to occur.

a. Individuals in a population vary in the trait selection would act on.

b. The variations are, in part, passed from parent to offspring.

c. In every generation, some organisms are better at surviving than others.

d. Differential survival and/or reproduction is associated with different states of the character trait. The organisms with the more favorable states of the trait have higher survival and reproductive rates.

Explain why at least one of the conditions of natural selection is not random.

a. Individuals vary. This is not the best choice. The variation in a population may be there due to random processes (e.g. mutation, gene flow); however, it could also be the legacy of non-random events.

b. Variations are in part passed from parent to offspring. This is not the best answer. There is some randomness in what alleles are passed on, but the phenotypes of the offspring are determined by what their parents pass on to them.

c. In every generation, organisms are better at surviving than others. This is a good choice! Differential survival and/or reproduction driven by a phenotypic trait is not random. A beneficial trait may increase survival under certain conditions.

d. Organisms with more favorable traits have higher survival and reproductive rates. This is a good choice! Differential survival and/or reproduction driven by a phenotypic trait is not random. For example, the trait could increase the likelihood of reproductive success by being attractive to potential mates. The trait itself must increase fitness with respect to other character states in order for this to be natural selection.

Those who are homozygous for the S allele of the beta-globin gene have a disease known as sickle cell anemia which can cause early death. Those who are homozygous for the A allele are susceptible to malaria. Those who are heterozygous (AS) do not get sickle cell anemia and are less susceptible to malaria in malarial regions. What type of natural selection is occurring in these malarial regions?

Balancing Selection

Each nucleotide has 10^-9 chances of having a point mutation. There are 2.75 billion base pairs (1 base pair = 2 nucleotides) in the rat genome. (Source: NIH) What is the potential number of point mutations that can occur in the rat genome during one replication? What can ensure disadvantageous mutations do not get passed to later generations in the population?

About 6 potential point mutations, disadvantageous mutations that do not increase survival and reproductive rates are selected against in the population hence those organisms are less likely to survive and pass on those mutations.

Which of the following is NOT an example of genetic drift?

a. The chances of Huntington's disease is 1/10,000 in the USA. On the other hand, in San Luis, Venezuela almost 25% of the residents have Huntington’s disease. Turns out, one of the people who founded San Luis carried an allele for Huntington’s.

b. A drought causes a lake to dry out leaving a population of fish exposed. Predators are then able to eat most of the fish.

c. Cheetahs display very low variations as a result of risk of extinction due to pressures from climate change and habitat loss from the past.

d. A light colored mouse moves to a population of dark colored mice and begins reproducing.

d. A light colored mouse moves to a population of dark colored mice and begins reproducing.

What does the molecular clock hypothesis imply?

The rate of substitution is equal to the rate of neutral mutations.

What is the difference between genetic drift and gene flow?

Genetic drift refers to a random event that reduces the variation within a population, whereas gene flow refers to the random migration of alleles from one population to another thereby increasing variation within populations but decreasing variation between populations.

In the absence of gene flow, two populations of mice isolated from each other will:

tend to become more different from each other.

In lectures and labs, we have seen how Hardy-Weinberg equilibrium can be disrupted by: mutation, natural selection, gene flow, and genetic drift. For each of the following mechanisms, identify its effect (increase, decrease, or no effect) on variation: a) within a population and b) between two populations. Explain briefly.

Mutation

- Within a population: increase variation because mutations can result in different phenotypes between individuals of a population

- Between two populations: no effect because mutations in one population do not necessarily affect individual in another population

Natural selection

- Within a population: decrease variation because individuals with phenotypes better suited for the environment have higher survival and reproductive rates so the surviving members of a population will not have too much phenotypic variations

- Between two populations: no effect because natural selection occurring in one population does not necessarily affect another population

Gene flow

- Within a population: increase variation because other individuals from another population can introduce new variations into a population

- Between two populations: decrease variation because when individuals move between populations the two populations will become more similar

Genetic drift

- Within a population: decrease variation because genetic drift events can cause certain variants to disappear or become larger in number hence individuals will end up having more similarities than differences

- Between two populations: no effect because genetic drift is concerned with variations within one population and does not account for individuals in another population