BIO202 22.2, 23.4

Which of the following are causes of evolutionary change?

-genetic drift -gene flow -mutation -natural selection

What is the frequency of the A1A2 genotype in a population compose of 20 A1A1 individuals, A1A2 individuals, and 100 A2A2 individuals?

0.4(Why: the calculation to determine the frequency of the A1A2 genotype is: 80 A1A2 individuals / (20+80+100) total individuals=0.4, the frequency of the A1A2 genotype.

A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.What proportion of the population is probably heterozygous (Aa) for this trait?

0.50

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3

Rank the following one-base point mutations (from most likely to least likely) with respect to their likelihood of affecting the structure of the corresponding polypeptide.1. insertion mutation deep within an intron2. substitution mutation at the third position of an exonic codon3. substitution mutation at the second position of an exonic codon4. deletion mutation within the first exon of the gene

4,3,2,1

Which of the following are basic components of the Hardy-Weinberg model?

Frequencies of two alleles in a gene pool before and after many random matings.(Why: Hardy and Weinberg were trying to determine how and whether allele frequencies in a population change from one generation to the next.

Which of the following evolutionary forces could create new genetic information in a population?

Mutation(Why: mutations, which are changes in a cell's DNA, can introduce new genetic information in a population.)

The three major mechanisms of evolution differ in how they work, and as a result often have different effects on a population. Review your understanding of natural selection, genetic drift, and gene flow by sorting the statements below into the correct bins. Drag each statement into the appropriate bin depending on whether it applies to natural selection, genetic drift, or gene flow.

Natural Selection Consistently causes a population to become better adapted to its environment A result of differential success in reproduction Cannot cause a harmful allele to become more common. Genetic Drift Responsible for the founder effect Responsible for the bottleneck effect Causes allele frequencies to fluctuate randomly. Gene flow Can introduce new alleles into a population's gene pool A result of the movement of fertile individuals or their gametes

Which of the following evolutionary forces results in adaptive changes in allele frequencies?

Selection(Why: selection is the only evolutionary force that consistently results in adaptation. Mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations.)

Which of the following statements is not a part of the Hardy-Weinberg principle?

The genotype frequencies in the offspring generation must add up to two.(Why: This statement is not true; the genotype frequencies in the offspring generation must add up to one.

A population of squirrels is preyed on by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome?

disruptive selection

Stabilizing selection __________.

favors intermediate variants in a population

The evolutionary effects of genetic drift are greatest when _____.

the population size is small

On an evolutionary tree __________

homologous characteristics form a nested pattern

Genetic variation _____.

must be present in a population before natural selection can act upon the population

The original source of all genetic variation is _____.

mutation

According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if _____ is the only process that affects the gene pool.

sexual selection

Selection that acts over evolutionary time to preserve traits that increase an individual's ability to mate is known as __________.

sexual selection

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

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, _____.

the allele's frequency should not change from one generation to the next

How does diploidy help to preserve genetic variation?

It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes.

What is the importance of neutral variation in evolution?

Neutral variation increases genetic variation, allowing a population to carry more alleles that may help it respond to environmental change.

What is the frequency of the A1 allele in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?

The frequency of the A1 allele is 0.3.(Why: the frequency of the A1 allele is p=(number of a1 alleles) / (total of all alleles) = [(2(20) + 80] / [(2 x 20) + (2 x 80) + (2 x100)]= 0.3

The fruit fly Drosophila melanogaster has an allele that confers resistance to DDT and similar insecticides. Laboratory strains of D. melanogaster have been established from flies collected in the wild in the 1930s (before the widespread use of insecticides) and the 1960s (after 20 years of DDT use). Lab strains established in the 1930s have no alleles for DDT resistance. In lab strains established in the 1960s, the frequency of the DDT-resistance allele is 37%. Which statement is correct?

The evolutionary fitness associated with the heritable trait of DDT resistance changed once DDT use became widespread.

What genotype frequencies are expected under Hardy-Weinberg equilibrium for a population with allele frequencies of p = 0.8 and q = 0.2 for a particular gene?

The expected genotype frequencies are 0.64, 0.32, and 0.04 for A1A1, A1A2, and A2A2, respectively.(Why: the expected frequency of the A1A1 genotype is p^2=(0.8)(0.8)=0.64; the expected frequency of the A1A2 genotype is 2pq=2(0.8)(0.2)=0.32; the expected frequency of the A2A2 genotype is q^2=(0.2)(0.2)=0.4. To verify your calculations, confirm that the three frequencies add up to one.

Which statement correctly describes the role of chance in evolution?

The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA.

Antibiotic resistance in bacteria is an example of which of the following?

directional selection

True of false? The Hardy-Weinberg model makes the following assumptions: no selection at the gene in question; no genetic drift; no gene flow; no mutation; random mating.

True(Why: these are 5 assumption of the Hardy-Weinberg model)

Which type of selection maintains stable frequencies of two or more phenotypic forms in a population?

balancing selection

An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake? An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?a genetic bottleneckdirectional selectiona founder eventdisruptive selection

bottleneck effect

Which of the following is the most predictable outcome of increased gene flow between two populations?

decreased genetic difference between the two populations

Which of the following descriptions illustrates phenotype variation caused by environment?

diet of caterpillars changes their morphology

Soon after the island of Hawaii rose above the sea surface (somewhat less than one million years ago), the evolution of life on this new island should have been most strongly influenced by _____.

founder effect

What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?

founder effect

Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing _____.

gene flow

Refer to the paragraph on dark-eyed junco birds. The UCSD campus male junco population tails were, on average, 36% white, whereas the tails of males from nearby mountain populations averaged 40-45% white. If this observed trait difference were due to a difference in the original colonizing population, it would most likely be due to _____

gene flow between populations

Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?

genetic drift

Generation-to-generation change in the allele frequencies in a population is _____.

microevolution

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

metaphrase I

Refer to the paragraph on dark-eyed junco birds. The UCSD campus male junco population tails are about 36% white, whereas the tails of males from nearby mountain populations are about 4045% white. The founding stock of UCSD birds was likely from the nearby mountain populations because some of those birds overwinter on the UCSD campus each year. Population sizes on the UCSD campus have been reasonably large, and there are significant habitat differences between the UCSD campus and the mountain coniferous forests; UCSD campus has a more open environment (making birds more visible) and a lower junco density (decreasing intraspecific competition) than that in the mountain forests. Given this information, which of the following evolutionary mechanisms do you think is most likely responsible for the difference between the UCSD and mountain populations?

natural selection

Crossing over, resulting in an increase in genetic variation, occurs between _____.

nonsister chromatids of homologous chromosomes