Ch 21: The Evolution of Populations Flashcards
In a population with two alleles, B and b, the allele frequency of b is 0.4. What would be the frequency of heterozygotes if the population is in Hardy-Weinberg equilibrium?
0.48
( 2 x 0.4 (b) x 0.6 (B) )
(- heterozygotes = 2pq)
Selection that acts over evolutionary time to preserve traits that increase an individual’s ability to mate is known as __________.
sexual selection
Genetic analysis of a large population of mink inhabiting an island in Michigan revealed an unusual number of loci where one allele was fixed. Which of the following is the most probable explanation for this genetic homogeneity?
A very small number of mink may have colonized this island, and this founder effect and subsequent genetic drift could have fixed many alleles.
An increase in the number of antibiotic-resistant individuals in a population of bacteria is an example of __________.
directional selection
In the context of a population, how is evolution defined?
Evolution is a change in a population’s allele frequencies over generations.
Assume a population is in Hardy-Weinberg equilibrium for a character with these genotypic frequencies: AA = 0.25, Aa = 0.50, and aa = 0.25. If you remove all the homozygous dominants and allow the remaining population to reproduce (again under Hardy-Weinberg conditions), what will be the frequency of homozygous dominants in the next generation?
0.11
(Since 2 x 0.25 = 0.50, one = 0.
AA (q) = 0, Aa (2pq) = 2/3 aa (p) = 1/3.
p^2 = 0.11)
A population of squirrels is preyed on by small hawks at maturity. The smaller adult squirrels can escape into burrows. The larger adult squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. This is an example of __________.
disruptive selection
A population of 15 birds inhabits a small island. Ten of the birds are dark brown, and five of them are light brown. By chance, two of the dark brown birds and three of the light brown birds die before producing any offspring. All of the birds in the next generation are dark brown. This change in phenotypic frequency can be attributed to __________.
genetic drift
The average heterozygosity of Drosophila melanogaster is estimated to be about 14%, which means that __________.
on average, 14% of a fruit fly’s gene loci are heterozygous
In a particular central African population, 4% are born with sickle-cell disease (they are homozygous recessive at a hemoglobin loci). If this population is in Hardy-Weinberg equilibrium, what percentage of the population is heterozygous at the relevant allele and has the selective advantage of being more resistant to malaria?
32%
(4% = 1/population = 0.04
sqrt 0.04 = 0.2
1-0.2 = 0.8
2 x 0.2 x 0.8 = 0.32 = 32%)
Which of the following mechanisms can alter allele frequencies?
All of the listed responses are correct.
Birds with average-size wings survived a severe storm more successfully than other birds in the same population with longer or shorter wings. If severe storms occur regularly, then over time, one should expect these storms to bring about __________.
stabilizing selection
Which of the following sets of conditions is required for Hardy-Weinberg equilibrium?
Random mating, no natural selection, and a large population
An earthquake hits a small island. All but a few individuals of a lizard species are eliminated in this catastrophe, and an allele is lost from the population. This is an instance of __________.
the bottleneck effect
Which of the following provides most of the genetic variation found among individuals in plant and animal populations?
Sexual reproduction
A scientist observes that the height of a certain species of asters decreases as the altitude on a mountainside increases. She gathers seeds from samples at various altitudes, plants them in a uniform environment, and measures the height of the new plants. All of her experimental asters grow to approximately the same height. From this she concludes __________.
the height variation she initially observed was an example of environmental influence
Which of the following is a true statement concerning sexual selection?
Sexual selection can result in sexual dimorphism.
In a large population of randomly breeding organisms, the frequency of a recessive allele is initially 0.3. There is no migration and no selection. Humans enter this ecosystem and selectively hunt individuals showing the dominant trait. When the gene frequency is reexamined at the end of the year, __________.
the frequency of the homozygous dominants will go down, the frequency of the heterozygous genotype will go down, and the frequency of the homozygous recessives will go up
