Campbell AP Biology Mastering Biology Chapter 23 Work
Which of these individuals is a homozygous genotype?
AA
Which of these gametes contain one or more recombinant chromosomes?
B, C, F, and G
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
A hypothetical population of 200 cats has two alleles, TL and TS, for a locus that codes for tail length. The table below describes the phenotypes of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Which statements about the population are true? Select the five statements that are true.
Heterozygotes make up 20% of the population. Homozygotes make up 80% of the population. In the entire cat population, 60% of the alleles are TS. In the entire cat population, the frequency of the TL allele is 0.4 . Assuming random mating, each gamete has a 40% chance of having a TL allele and a 60% chance of having a TS allele.
Which of the following evolutionary forces could create new genetic information in a population?
Mutation
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 )causes allele frequencies to fluctuate randomly )responsible for the bottleneck effect Gene Flow: )a result of the movement of fertile individuals or their gametes )can introduce new alleles into a population's gene pool
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
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.
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
The ease with which humans travel across the globe is likely to increase _____.
gene flow
All the genes in a population are that population's _____.
gene pool
Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.
genetic drift
Generation-to-generation change in the allele frequencies in a population is _____.
microevolution
The original source of all genetic variation is _____.
mutation
Crossing over, resulting in an increase in genetic variation, occurs between _____.
nonsister chromatids of homologous chromosomes
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 reproduction
A mutation occurs when _____.
there is a change in the DNA sequence of a gene
Which type of selection tends to increase genetic variation?
Disruptive 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.
Rabbit ear size tends to decrease as latitude increases. This is an example of _____.
a cline
Which of the following are causes of evolutionary change?
genetic drift natural selection mutation gene flow
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
A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?
0.42
In human gamete production there is an average of _____ crossover events per chromosome pair.
2-3
Enter the values for the expected frequency of each genotype: TLTL, TLTS, and TSTS. Enter your answers numerically to two decimal places, not as percentages. For help applying the Hardy-Weinberg equation to this cat population, see Hints 1 and 2.
.16 .48 .36
In the beetles described in the animation, there were two alleles for color, brown and green. Suppose that you discover a very small population of these beetles, consisting of the individuals shown below. How can you calculate the frequency of each allele in this population? Drag the terms or numbers on the left to the appropriate blanks on the right to complete the sentences. Not all terms will be used.
1. brown alleles 2. 8 3. 20 4. 0.4 5. 0.6
A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is
1.) .84 2.) .16 3.) .36 4.) .6 5.) .4 6.) .48 7.) .16 8.) .4
Imagine that you are studying a gene with two alleles, R and r. What genotypes (sets of alleles) would you expect to find in the offspring of two Rr parents? What is the probability of producing an offspring with each of the possible genotypes? The figure shows how these probabilities can be calculated. Drag the percentages on the left to answer the questions on the right. Percentages may be used once, more than once, or not at all.
1.) 50% 2.)50% 3.) 25% 4.) 25% 5.) 50%
In Part A, you looked at a single genetic cross involving two parents of genotype Rr. Imagine now that instead of a single mating, you consider all the matings that occur in a population, and all the offspring that are produced. The figure at right shows a population of flowers with two alleles for color, a red allele CR and a white allele CW . The allele frequencies across the entire population are 80% CR and 20% CW . In other words: The frequency of the CR allele, called p, is 0.8. The frequency of the CW allele, called q, is 0.2. If the population is not evolving, then the population is said to be in Hardy-Weinberg equilibrium. In this case, the Hardy-Weinberg principle tells us that offspring inherit alleles as if they were drawn from the gene pool at random. This means that: The proportion of individuals with genotype CRCR is expected to be p2. The proportion of individuals with genotype CRCW is expected to be 2pq. The proportion of individuals with genotype CWCW is expected to be q2. Furthermore, if a population is in Hardy-Weinberg equilibrium, the allele frequencies (p and q) and the genotype frequencies stay the same from one generation to the next.
1.) 80% 2.) 20% 3.) 64% 4.) 4% 5.) 32% 6.) 80% 7.) 20%
One out of 10,000 babies born in North America is affected by cystic fibrosis, a recessive condition. Assuming that the North American human population is in Hardy-Weinberg equilibrium for this trait, what percentage of the population is heterozygous for this trait? (Remember the equation for a population in Hardy-Weinberg equilibrium: p2 + 2pq + q2 = 1.)
2%
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
Which of the following evolutionary forces consistently results in adaptive changes in allele frequencies?
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
Genetic drift is a process based on _____.
the role of chance
Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population?
Alleles that promote "tallness" will decrease in frequency.
A hypothetical population of 300 wolves has two alleles, FB and FW, for a locus that codes for fur color. The table below describes the phenotype of a wolf with each possible genotype, as well as the number of individuals in the population with each genotype. Which statements accurately describe the population of wolves?
Based on the equation for Hardy-Weinberg equilibrium, the expected number of wolves with the FBFB genotype is 12. Based on the equation for Hardy-Weinberg equilibrium, the expected number of wolves with the FBFW genotype is 96. The population may be evolving because the actual number of individuals with each genotype differs from the expected number of individuals with each genotype. The population is not at Hardy-Weinberg equilibrium.
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
Populations evolve for many reasons. Suppose there is a population of plants that have either purple flowers or white flowers, and the allele for purple flowers is dominant. This means that plants with two purple alleles have purple flowers. Plants with one purple allele and one white allele also have purple flowers. Only plants with two white alleles have white flowers. For each event or condition described below, answer the following questions. Which mechanism of evolution is at work? How does this event affect the population's gene pool? Do the frequencies of the two alleles change, and if so, how? 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.) allale frequences change but not predictably g.) natural selection h.)frequency of purple allele increases i.) gene flow j.) frequency of white allele increases
In Part B, you learned that if a population is in Hardy-Weinberg equilibrium, the allele and genotype frequencies stay the same from one generation to the next. A population in Hardy-Weinberg equilibrium is not evolving. Five conditions have to be satisfied in order for a population to be in Hardy-Weinberg equilibrium: no mutations random mating no natural selection extremely large population size no gene flow If any of these conditions are violated, the population does not stay in Hardy-Weinberg equilibrium, and allele frequencies and genotype frequencies may change from one generation to the next. Explore some potential departures from Hardy-Weinberg equilibrium by completing the table below. Drag the labels to the table below to describe how allele frequencies would be affected under different conditions. Remember that p is the frequency of the CR allele, and q is the frequency of the CW allele. Labels may be used once, more than once, or not at all.
a.) p will decrease and q will increase b.) p will increase and q will decrease c.) changes in p and q cannot be predicted d.) p will increase and q will decrease
Homologous pairs of chromosomes are lined up independently of other such pairs during _____.
metaphase I
