Population: Evolution

A population of domesticated sheep becomes stranded on a rocky island. Over many years, the physical traits of the sheep population are altered. Their wool became thicker and darker, their hooves became deeper and sturdier, and their ears became smaller and rounder.

These changes are an example of which process?

• evolution by artificial selection, because the changes in traits are unrelated to fitness

• evolution by artificial selection, because sheep are domesticated animals that were bred by humans

• evolution by natural selection, because the environment selected traits that increased fitness

• changes that do not involve evolution, because the population remained the same species

• changes that do not involve evolution, because the changes were too insignificant to affect fitness

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The graphs below show the changes in crab color at one beach from 1950 to 1990.

• Stabilizing selection, because one crab color was preferred over other colors.

• Stabilizing selection, because two crab colors were preferred over other colors.

• Directional selection, because two extreme colors were preferred over the more moderate color.

• Disruptive selection, because two extreme colors were preferred over the more moderate color.

• Adaptive radiation, because crabs of a single color evolved to form crabs of several colors.

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Two species each carry a gene for the production of the same enzyme. The DNA sequences of the two genes are very similar, but differ in several base pairs. Comparing and analyzing the DNA sequences would be MOST useful for making which of these inferences?

• determining whether or not the species share a common ancestor

• determining whether or not the species use the same genetic code

• identifying the physical differences in the bodies of the two species

• identifying the physical traits of the most recent common ancestor of the species

• approximating the time when the most recent common ancestor of the species was alive

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A gene for a trait has a dominant allele (B) and a recessive allele (b). The table describes the frequency of each allele in a population over a 60-year period. Assume that the size of the population remained relatively constant during this time.

• A mutation made the heterozygous genotype Bb more advantageous to individuals.

• The environment changed so that the heterozygous genotype Bb provided an advantage to individuals.

• The environment changed so that the homozygous recessive genotype bb provided an advantage to individuals.

• Random chance or genetic drift made the homozygous recessive genotype bb more common in the population.

• A mutation made allele B lethal, or deadly, to any individual who carried it.

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Darwin proposed that the Galapagos Islands were settled by a small population of a single species of finch. This species was the ancestor of all the finch varieties that Darwin had observed on the islands. According to the modern theory of evolution, which of the following events occurred during the evolution of the Galapagos finches?

I. Each finch species developed a unique genetic code for interpreting DNA.

II. Each finch species developed slightly different genes, due to mutations and sexual reproduction.

III.Subsets of the original population of finches became reproductively isolated from one another.

• I. only

• I. and II.

• II. and III.

• III. only

• I., II., and III.

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Naomi runs a computer simulation for a population of mice in a meadow ecosystem. The simulation begins with 100 mice, divided equally among brown and white variants. The variants are similar apart from their body color. A mating of a white and brown mouse may produce a speckled mouse, which is mostly brown with some white markings.

The table shows the numbers of each mouse variant over 7 reproduction cycles. Only adult mice are reported in the table.

• After cycle 2, a disease arrived that affected white mice only.

• After cycle 2, a predator arrived that saw white mice more easily than brown mice.

• After cycle 4, brown mice and white mice began living separately, and stopped interbreeding.

• After cycle 4, a predator arrived that saw white mice more easily than brown mice.

• After cycle 4, a disease arrived that affected brown mice only.

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Darwin developed a concept called geographic isolation to explain how species developed. Which observation provided the STRONGEST evidence for this concept?

• Native island species tend to be identical to species on the mainland and on neighboring islands.

• Native island species tend to be different from related species on the mainland and from neighboring islands.

• Fossils show that ancient species differed in many ways from species today.

• Some island species arrived naturally, while others were introduced through human activity.

• Structural variations among island species, such as the beaks of Galapagos finches, tend to help the animals survive.

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A population of a species of butterfly is released on a tropical island. Which condition is necessary for evolution by natural selection to alter the butterfly population over time?

• genetic variation among the members of the population

• a lack of competitors for food, water, and other resources

• relatively stable weather on the tropical island

• genetic uniformity among the members of the population

• approximately equal numbers of male and female members of the population

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Populations of two species of grasshoppers are introduced to a meadow ecosystem. Each species is adapted to eat grass and similar plants of the meadow, and they fill the same niche. According to Darwin’s ideas about competition, which of the following changes is MOST likely to occur?

• Only one population will thrive in the meadow; the other population will decrease to zero.

• Either both populations will thrive in the meadow, or neither population will thrive.

• Both populations will eventually remain constant at the same non-zero number.

• Both populations will eventually remain constant, but at different non-zero numbers.

• Both populations will increase and decrease in a cycle.

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A female fish may lay thousands of eggs at once. Which additional statement about fish is MOST useful for explaining how fish species can evolve by natural selection?

• All of the fish eggs are genetically identical with one another and with the female parent fish.

• The environment cannot support unlimited growth of the fish population, so only some fish eggs will mature to adults.

• After the female fish lays a clutch of eggs, neither parent tends to or cares for the eggs or offspring.

• Fish eggs will develop into embryos only if they are fertilized by sperm from the male fish.

• In certain species and under certain circumstances, a fish can switch genders.

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