A study showed that the mortality risk for human babies goes up as birth weight decreases below the average. Another study shows an increase in mortality risk as birth weight increases above the average. What can be said about human birth weight?
It is a trait that is shaped by stabilizing selection
Refer to the graphs below. Identify the type of selection indicated by the three graphs
A=directional selection; B=disruptive selection; C=stabilizing selection
In order for natural selection to change a trait within a population, what must be true about the trait?
The trait must have a genetic basis
Refer to the table below. Male birds in a population show a distribution of feather colors from dull to bright red. A biologist kept track of the numbers of males in three categories of feather color over seven generations, as shown in the table. Which of the following conclusions is consistent with the data?
The data provide evidence of disruptive selection.
A lizard population has three alleles for a particular gene—X1, X2, and X3. Two of these alleles are neutral (X1 and X2) and the third is deleterious (X3). In which of the following scenarios would you say that genetic drift is definitely operating?
Over time, the frequencies of X1 and X2 decrease, and the frequency of X3 increases.
What feature of a population makes it vulnerable to genetic drift?
Number of individuals in a population.
Refer to the table below. Four different populations of an owl species were studied. Data were collected on population sizes and the frequencies of alleles for one gene. The gene is not known to be under any selective pressures. If genetic drift is the only mechanism operating to change these allele frequencies over time, which population can be expected to show the greatest change and which can be expected to show the least change over time?
Greatest change=A; least change=C
Which of the following about genetic drift is true?
Genetic drift affects allele frequencies within a population.
Which statement about the genomes of organisms is false?
The total size of the genome of eukaryotes varies little from organism to organism
______ selection operates if individuals within a population with the smallest and largest body sizes have fewer offspring than those of normal body size
The frequency of one allele for a given gene locus with two alleles (A at frequency p and a at frequency q) in a population is known. Assume Hardy-Weinberg conditions hold true. Which statement is false?
The frequency of heterozygotes is given by (p + q)/N, where N is the number of individuals in the population.
The Hardy-Weinberg equilibrium is not applicable under which condition?
Asexual reproduction
A neutral mutation
is fixed in a population at a rate equal to the mutation rate
Which evolutionary process adapts populations to their environments?
Natural selection
You discover a population of seals and find it to be at Hardy-Weinberg equilibrium with respect to the A locus. Suppose that there are two alleles at this locus and the frequency of one of those alleles (the a-6 allele) is 0.4. Of the individuals that carry at least one a-6 allele, what percent are homozygotes?
Sexual recombination
can result in the elimination of harmful mutations
Mistakes in the replication of DNA
provide genetic variation
Which statement about synonymous mutations is true?
They do not change the phenotype
Refer to the figure below. What is occurring at step 2?
Directional selection
Refer to the figure below. Which description of the gene pool shown is correct
Frequency of X1X3 = 0.10
Which statement about selection is true?
Disruptive selection is the only type of selection that can produce a bimodal distribution.
Which observation would most seriously challenge the hypothesis that most noncoding DNA is slightly deleterious?
Species with larger population sizes have more noncoding DNA
Gene families are groups of _______ genes that arose by _______ and _______.
homologous; gene duplication; sequence evolution
A gene involved in neural development shows three times as many synonymous site substitutions than nonsynonymous ones. A likely explanation is that this gene
is under purifying selection
The frequency of an allele in a population of manatees is 0.15. If the population is at Hardy-Weinberg for this locus, what number of 600 individuals should be homozygous for this allele?
Which phenomenon is not an evolutionary mechanism?
Random mating
In explaining what we now call evolution, Darwin often used the phrase “descent with modification.” Fundamental to this idea is that
divergent species share a common ancestor
Suppose the size of a population of mustard plants is 6,000. According to genetic drift theory, what is the probability that a newly-arisen mutation will become fixed in this population?

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