Bio 100 - Chapter 13

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

2-3 [ These crossover events increase the genetic variation among gametes. ]

Which of these individuals is a homozygous genotype?

AA [ When both of the alleles of a given gene pair are the same, the individual is homozygous for that gene. ]

Suppose that every few years, all people over 6 feet tall do not have any children. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency. [ A reduction in "tallness" alleles is the change expected as a result of this type of selection. ]

Small lizards have difficulty defending their territory, but large lizards are more likely to be preyed upon by owls. Which type of selection would act on body size in these lizards under these conditions?

Stabilizing selection [ Stabilizing selection does not change the mean of the population; only the extreme phenotypes (large and small lizards) become less common ]

The human immune system cannot effectively suppress the HIV virus on its own. What key feature of HIV makes it so hard to beat?

The HIV virus has an extremely high rate of mutation.

The wing of a bat is homologous to the _____ of a whale.

flipper [ The bones of a bat wing and a whale flipper are homologous. ]

The ease with which humans travel across the globe is likely to increase _____.

gene flow [ When people travel or migrate, they take their alleles with them. ]

All the genes in a population are that population's _____.

gene pool [ All the alleles of all the genes of a population make up a gene pool. ]

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.

genetic drift [ Modern travel and migration decreases the chances of there being a small, isolated population. ]

Which of the following are causes of evolutionary change?

genetic drift, natural selection, gene flow, mutation

In a population with brown and green alleles for color, genetic drift

has more effect on the evolution of a small population. [ Genetic drift affects the evolution of small populations more than it affects the evolution of large populations. ]

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

metaphase I [ This describes metaphase I. ]

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

microevolution [ Generation-to-generation change in the allele frequencies in a population is the definition of microevolution. ]

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

nonsister chromatids of homologous chromosomes [ This process produces chromosomes containing genes inherited from both parents. ]

If color is an inherited trait in beetles, and birds are more likely to eat brown beetles than green beetles,

the frequency of the green allele will increase. [ If birds are more likely to eat brown beetles than green beetles, then green beetles will survive and reproduce more than brown beetles. This causes the frequency of the green allele to increase. ]

True or False. In the example described in the tutorial, the red amoebas survived the catastrophic event, and all future generations of amoebas were red because the red amoebas had a higher reproductive rate than the blue ones.

False [ After the catastrophic event, all future generations of amoebas were red because all blue amoebas died during the catastrophe. ]

Color is an inherited trait in beetles. If brown beetles move into a population from a nearby island, which of the following statements is correct?

Gene flow causes the frequency of the brown allele to increase. [ Gene flow occurs when individuals move into or out of a population, changing the allele frequencies in the population. In this case, new brown beetles in the population cause the frequency of the brown allele to increase. ]

Remember that color is an inherited trait in beetles. Which of the following is an example of natural selection?

Green beetles leave more offspring than brown beetles because they are better at finding food. [ Natural selection occurs when organisms with one inherited trait survive and reproduce more than organisms with other traits. ]

As proposed by Darwin, what sorts of traits are favored by natural selection?

Heritable traits that help individuals survive and reproduce more successfully than others in the same population.

Which of the following events could NOT be caused by a population bottleneck?

Increased population size [ By definition, a population bottleneck dramatically reduces the size of a population. ]

Genetic drift is a process based on _____.

the role of chance [ Genetic drift requires a small sample size. ]

A mutation occurs when _____.

there is a change in the DNA sequence of a gene [ This is the definition of mutation. ]

The evolution of populations due to chance is

genetic drift. [ Genetic drift describes the evolution of a population due to chance. ]

In a species of snail, dark-shelled individuals are better hidden from bird predators in the shady forest, while light-shelled individuals are better hidden in well-lit brushy edge areas. If there were no areas of intermediate brightness in this habitat, which type of selection would act on shell color in these snails?

Disruptive selection [ Disruptive selection causes both extreme phenotypes (light and dark shells) to be favored over the intermediate phenotype. ]

Imagine that four people are infected with HIV from a common source (an infected blood sample). Initially, the patients' HIV populations are genetically identical. By the time they develop full-blown AIDS, how would the viral populations of the four patients compare?

Each patient's viral population would be unique, specifically adapted to deal with—and overcome—his or her unique immune system responses.

Natural selection is best described as _____.

a filtering process that fine-tunes the traits of populations by sorting among existing, randomly produced variations

Which of the following statements about the amoeba population described at the end of the tutorial is true?

It is more vulnerable to extinction due to lack of genetic variation. [ The amoebas might not have the variation necessary to adapt to future changes in the environment. ]

HIV has become an important source of mortality for humans. If AIDS persists as a major factor for humans for many generations in the future, natural selection theory predicts that _____.

any heritable traits that help humans survive and reproduce in the presence of AIDS should become more frequent over time