Moodle Quiz Questions Flashcards
How do you calculate the total number of alleles present at a single locus in a population?
a. It varies depending on the locus
b. For a diploid population it’s the total population size Xs 2
c. It’s the same as the population size
b. Population size = N = the number of individuals in the population. Each diploid individual has 2 alleles at each locus, therefore the population has 2N alleles at each locus.
Genetic drift has a bigger effect on allele frequencies in a _______ population.
a. larger
b. smaller
b. Genetic drift is a change in allele frequency due to chance. Random events can have a bigger effect in a smaller population.
Do deleterious alleles ever increase in frequency in a population?
a. No. Natural selection prevents it.
b. Yes, sometimes.
b. If an allele is not too severely deleterious, it can increase in frequency due to genetic drift. [There’s also mutation, which causes a new allele’s frequency to increase from 0 to 1/(2N).]
True/False: For natural selection to operate, there needs to be variation among individuals in a population.
TRUE, natural selection can only work if there are differences between individual organisms in the traits they possess
True/False: For natural selection to operate, the heritable variation within a population must affect the likelihood that an individual can survive to adulthood (reproductive age).
FALSE natural selection can also work if the variation affects number of offspring, or generation time, or anything else that affects reproductive success. Survival is just one component of reproductive success.
Because of a drought in 1977, a population of Galapagos finches wound up having a larger average beak size
(pp. 456-458.). Average beak size increased because
a. individual birds’ beaks got bigger because they were forced to crack tough seeds
b. bigger-beaked birds were much better at reproducing than smaller-beaked birds
c. most of the smaller-beaked birds died
c
True/False: Evolution has resulted in a “ladder” of living beings, with more highly evolved species towards the top.
FALSE Evolution results in a tree, not a ladder
If the frequency of the B allele is 0.2, what is the frequency of the BB homozygote?
a. .004
b. .02
c. .04
d. .2
e. .4
c. If you draw one allele (gamete) from the population at random, the probability of drawing allele B is 0.2. If you draw 2 alleles (2 gametes to make a zygote), the probabability that both are B is equal to the probability that the first one is B (0.2) times the probability that the 2nd one is B (0.2). The genotype frequency of the BB homozygote = (allele frequency of B) squared = 0.2 X 0.2 = 0.04 = 4%.
Evolutionary biologists working with a wild population often report the population’s “heterozygosity”. This is simply the proportion of individuals that are heterozygous (for any combination of alleles) at a given locus. (Often it is measured at several different loci and then the average heterozygosity across all the different loci is reported.) In general we should expect heterozygosity to be ____________ correlated with population size.
a. positively
b. negatively
c. not at all
a. Large populations usually have more genetic diversity, which would lead to (be measurable as) higher heterozygosity.
Of the types of natural selection on continuous traits, which type does NOT reduce the amount of genetic variation underlying the trait?
a. directional selection
b. stabilizing selection
c. disruptive selection
c.
True/false: Rare-allele advantage is a form of balancing selection
True. If rare alleles have a selective advantage this will maintain genetic diversity at one locus.
Birth weight in humans is an example of a trait that is under
a. directional selection
b. stabilizing selection
c. disruptive selection
b. This example is given on p. 473
True/False: Stabilizing selection is a form of balancing selection
False. Stabilizing selection stabilizes a multigenic TRAIT and REDUCES variation. Balancing selection maintains intermediate ALLELE FREQUENCIES and MAINTAINS OR INCREASES variation. See pp. 447.
True/False: Heterozygote advantage is a form of balancing selection.
True. Balancing selection is selection that maintains genetic diversity at a single locus, and selection in favor of heterozygotes is a form of balancing selection
If you are doing an artificial selection experiment, which lab population would you expect would show a greater response to selection (greater change in mean trait value under directional selection)?
a. a lab population that was sampled from a small wild population
b. a lab population that was sampled from a large wild population
b. A lab population that was sampled from a large wild population would likely have greater genetic diversity across the whole genome and therefore, all else being equal, would be more likely to show a greater response to selection for any particular trait.
