Chapter 21 Mastering Biology

The frequency of the brown allele in this beetle population is

0.4

Why is the enzyme lactase necessary to digest dairy products?

Lactase breaks down lactose into smaller molecules that can be absorbed by the cells that line the small intestine.

How do you expect the frequencies of the CG and CY alleles to change beyond day 21?

The frequency of the CY allele will decrease, and the frequency of the CG allele will increase.

Lactose intolerance in infants is more common in the population today than it was a hundred years ago. Why?

Today there are alternatives to breast milk, such as lactose-free formula and soy milk, so lactose intolerant infants can survive

To calculate the frequency of the brown allele, count the number of ___________ and divide by the total number of alleles in this population.

brown alleles

In which country would you most likely find a higher incidence of lactase persistence?

in a Scandinavian country where people historically raised dairy cattle and made cheese

Drag the labels to their appropriate locations in the table below. Drag the pink labels onto the pink targets in the table to indicate which mechanism of evolution is at work. Then drag the blue labels onto the blue targets to indicate the effect on allele frequencies. Labels can be used once, more than once, or not at all.

a) natural selection b) frequency of white allele increases c) genetic drift d) frequency of purple allele increases e) genetic drift f) allele frequencies change but not predictably g) natural selection h) frequency of purple allele increases i) gene flow j) frequency of white allele increases

Fill in the table with the observed frequencies for each genotype at day 7. Enter your answers to three decimal places.

0.227, 0.514, 0.259

Which type of selection tends to increase genetic variation?

Disruptive selection

Why should we not view lactose intolerance as a disease in adult humans?

Adult humans did not consume dairy products until fairly recently in our evolutionary history.

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

Mutation

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

Selection

In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following?

The value of a particular characteristic; characteristics of an organism can include such traits as size and color.

True or 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

Fill in the table with the expected frequencies for each genotype. Enter your answers to three decimal places.

0.234, 0.499, 0.266

Fill in the table with the observed frequencies for each genotype at day 21. Enter your answers to three decimal places.

0.272, 0.613, 0.116

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

0.4

The first step in testing whether a population is in Hardy-Weinberg equilibrium is to calculate the allele frequencies in the population. Remember that the frequency of an allele in a gene pool is the number of copies of that allele divided by the total number of copies of all alleles at that locus. Using the day 7 data, what is the frequency of the CG allele (p)?

0.484

Using the day 7 data, what is the frequency of the CY allele (q)?

0.516

The frequency of the green allele in this beetle population is

0.6

Drag the numbers on the left to the appropriate blanks on the right to answer these questions about a hypothetical cat population. Answers can be used once, more than once, or not at all.

1) 0.84 2) 0.16 3) 0.36 4) 0.60 5) 0.40 6) 0.48 7) 0.16 8) 0.40

In this beetle population, the total number of alleles is

20

In this beetle population, the number of brown alleles is

8

What hypothesis could explain the data for days 7 and 21?

At day 7, CYCY individuals were not being selected against because they had not used up the supply of food that was stored in the seed; by day 21, they had run out of stored food and many plants were not surviving.

Long necks make it easier for giraffes to reach leaves high on trees, while also making them better fighters in "neck wrestling" contests. In both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today?

Directional selection

Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers?

Disruptive selection

True or false? Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population.

False

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

How did Dr. Allison test his hypothesis that sickle cell disease was connected to malaria?

He evaluated blood samples for malaria parasites and the presence of sickle cells. He expanded his study area beyond Kenya to the rest of East Africa to see if malaria and sickle disease were connected.

In 1949, Dr. Tony Allison observed a high frequency of Kenyans carrying the sickle cell allele in coastal areas and near Lake Victoria, but a lower frequency in the highlands. What did he hypothesize?

He hypothesized that there was a connection between malaria and sickle cell disease.

How does Dr. Allison's work provide an example of natural selection in humans?

In areas without malaria, individuals with two sickle cell alleles reproduced at lower rates than those without sickle cell disease. In areas with malaria, individuals with one sickle cell allele reproduced at higher rates than those with no sickle cell alleles.

In some populations, 1 in 500 people have sickle cell disease. What reason does the film give for why a potentially deadly, inherited disease is found at such high frequencies?

Individuals with one sickle cell allele are protected from malaria and do not have sickle cell disease, thus keeping the allele in the population.

Most people are lactose intolerant as adults, but nearly everyone produces sufficient lactase as an infant. However, in some cases, genetic mutations can occur that make an infant lactose intolerant. From an evolutionary perspective -- over thousands of years -- why would lactose intolerance in infants be very rare in the population?

Lactose intolerant infants could not digest breast milk and therefore usually died, never having the chance to pass the mutation on to their children.

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, and cannot cause a harmful allele to become more common Genetic Drift: causes allele frequencies to fluctuate randomly, responsible for the bottleneck effect, responsible for the founder effect Gene Flow: can introduce new alleles into a populations gene pool, a result of the movement of fertile individuals or their gametes

Compare sickle cell disease and malaria.

Sickle cell disease and malaria are both potentially lethal diseases

Small Aristelliger lizards have difficulty defending territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these lizards?

Stabilizing selection

Women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies?

Stabilizing selection

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.

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.

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.

If a person has two normal copies of the hemoglobin allele, which statements are true?

The person is susceptible to malaria. The person is homozygous at the hemoglobin locus.

Is the seedling population at day 21 in Hardy-Weinberg equilibrium, or is evolution occurring?

The population is evolving, and there appears to be selection against genotype CYCY

At day 7, is the seedling population in Hardy-Weinberg equilibrium, or is evolution occurring?

The population is in Hardy-Weinberg equilibrium.

Predict what will happen to the frequency of the sickle cell allele in areas where malaria has been eradicated.

The sickle cell allele will decrease in frequency.

How do lactase supplements help people who are lactose intolerant?

The supplements provide the enzyme that breaks down the lactose in dairy products.

When should a lactase supplement be taken in order to be most effective, and why?

at the same time the dairy product is consumed, so that the lactase will be in contact with the lactose

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

microevolution