LSU BIOL 1202 - Ch. 23 Mastering Biology Answers
Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?
genetic drift
Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer or more than this have reduced fitness. Which of the following terms best describes this situation?
stabilizing selection
Women often have complication 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 situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?
founder effect
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
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
The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. The outcome of the conflict between bacteria and bacteriophage at any point in time results from _____.
frequency-dependent selection
The ease with which humans travel across the globe is likely to increase _____.
gene flow
Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.
genetic drift
Genetic drift is a process based on _____.
the role of chance
A mutation occurs when _____.
there is a change in the DNA sequence of a gene
Consider a population of wildflowers in which the frequency of the red allele CR is p = 0.7. What is the frequency of the white allele (CW ) in this population?
0.3
This Punnett square shows allele combinations for all possible genetic crosses in the wildflower population described in Part A. What are the expected genotype frequencies in the offspring generation?
0.49 CRCR (red flowers), 0.42 CRCW (pink flowers), 0.09 CWCW (white flowers)
Considering the same population of cats as in Part A, what is the expected frequency of each genotype (TLTL, TLTS, TSTS ) based on the equation for Hardy-Weinberg equilibrium? Keep in mind that you just learned in Part A that: - The allele frequency of TL is 0.4. - The allele frequency of TS is 0.6. The equation for Hardy-Weinberg equilibrium states that at a locus with two alleles, as in this cat population, the three genotypes will occur in specific proportions: - p2+2pq+q2=1 Enter the values for the expected frequency of each genotype: TLTL, TLTS, and TSTS. 1. TLTL 2. TLTS 3. TSTS
1. 0.16 2. 0.48 3. 0.36
In human gamete production there is an average of _____ crossover events per chromosome pair.
2-3
Consider a wildflower population with the following allele and genotype frequencies. Frequency of the CR allele: p = 0.6 Frequency of the CW allele: q = 0.4 Frequency of CRCR : 50% Frequency of CRCW : 20% Frequency of CWCW : 30% Is this population in Hardy-Weinberg equilibrium?
No, the frequency of genotype CRCW is too low
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
Which statement about variation is true?
all new alleles are the result of nucleotide variability
You sample a population of butterflies and find that 56% are heterozygous at a particular locus. What should be the frequency of the recessive allele in this population?
allele frequency cannot be determined from this information
In evolutionary terms, an organism's fitness is measured by its _____.
contribution to the gene pool of the next generation
Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to _____.
directional selection
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
In the United States, the parasite that causes malaria is not present, but it is present in African-Americans whose ancestors were from equatorial Africa. What should be happening to the sickle-cell allele in the United States, and what should be happening to it in equatorial Africa?
directional selection; stabilizing selection
Which type of selection tends to increase genetic variation?
disruptive selection
Swine are vulnerable to infection by bird flu virus and human flu virus, which can both be present in an individual pig at the same time. When this occurs, it is possible for genes from bird flu virus and human flu virus to be combined. If the human flu virus contributes a gene for Tamiflu resistance (Tamiflu is an antiviral drug) to the new virus, and if the new virus is introduced to an environment lacking Tamiflu, then what is most likely to occur?
if the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency
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. It fosters the exchange of genes between different populations
Homologous pairs of chromosomes are lined up independently of other such pairs during _____.
metaphase I
Which of the following evolutionary forces could create new genetic information in a population?
mutation
What is the only evolutionary mechanism that consistently leads to adaptive evolution?
natural selection
Crossing over, resulting in an increase in genetic variation, occurs between _____.
non-sister chromatids of homologous chromosomes
Which of the following evolutionary forces consistently results in adaptive changes in allele frequencies?
selection
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
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 A1A2 genotype in a population compose of 20 A1A1 individuals, A1A2 individuals, and 100 A2A2 individuals?
0.4
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 is the estimated frequency of allele A in the gene pool?
0.50
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
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
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
The evolutionary effects of genetic drift are greatest when _____.
the population size is small
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype?
0.81
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. What is the frequency of cats with long tails in the population? 2. What is the frequency of cats with short tails in the population? 3. What is the frequency of cats that are homozygous dominant in the population? 4. What is the frequency of the T allele in the gene pool of this population? 5. What is the frequency of the t allele in the gene pool of this population? 6. Use the Hardy-Weinberg equation to predict the frequency of heterozygous cats in the next generation. 7. Use the Hardy-Weinberg equation to predict the frequency of homozygous cats in the next generation. 8. Use the Hardy-Weinberg equation and your answer to question 7 to estimate the frequency of the recessive allele t in the next generation.
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 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. What is the probability that a gamete (egg or sperm) from this population carries a CR allele? 2. That a gamete from this population carries a CW allele? 3. Of all the offspring resulting from all the matings in this population, what percentage should have the genotype CRCR? 4. What percentage should have the genotype CWCW? 5. What percentage should have the genotype CRCW? 6. In the offspring generation, what is the frequency of the CR allele? 7. In the offspring generation, what is the frequency of the CW allele?
1. 80% 2. 20% 3. 64% 4. 4% 5. 32% 6. 80% 7. 20%
Which of these individuals is a homozygous genotype?
AA
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
You are maintaining a small population of fruit flies in the laboratory by transferring the flies to a new culture bottle after each generation. After several generations, you notice that the viability of the flies has decreased greatly. Recognizing that small population size is likely to be linked to decreased viability, the best way to reverse this trend is to _____.
cross your flies with flies from another lab
All the genes in a population are that 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 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
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 is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (aa) has not changed over time?
the two phenotypes are about equally adaptive under laboratory conditions
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? Select the four statements that are true.
- 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 is not at Hardy-Weinberg equilibrium - The population may be evolving because the actual number of individuals with each genotype differs from the expected number of individuals with each genotype.
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?
- 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
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of the allele a is 0.3. What is the frequency of individuals that are homozygous for this allele?
0.09
In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population?
0.80
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. 1. According to Mendel's law of segregation, what is the probability that a gamete (egg or sperm) from an Rr parent carries an R allele? 2. What is the probability that a gamete from an Rr parent carries an r allele? 3. When an Rr female is crossed with an Rr male, what is the probability of producing a homozygous dominant (RR) offspring? 4. What is the probability of producing a homozygous recessive (rr) offspring? 5. What is the probability of producing a heterozygous (Rr) offspring?
1. 50% 2. 50% 3. 25% 4. 25% 5. 50%
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: 1. no mutations 2. random mating 3. no natural selection 4. extremely large population size 5. 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. 1. Mutation: Red alleles (cR) mutate into white alleles (cW) more often than the opposite. 2. Non-Random Mating: Red flowers reproduce mainly with other red flowers, and white flowers reproduce mainly with other white flowers. 3. Natural Selection: During an extreme heat wave, plants with red flowers survive better than plants with white flowers. 4. Small Population Size: A storm kills many plants at random, leaving only a few plants in the population. 5. Gene Flow: Workers from a nearby greenhouse track white flower seeds into this populations habitat.
1. p will decrease and q will increase 2. frequency of plants with pink flowers (cRcW) will be much less than 2pq (GIVEN) 3. p will increase and q will decrease 4. changes in p and q cannot be predicted 5. p will decrease and q will increase
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 statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?
each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted
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
In the formula for determining a population's genotype frequencies, the "2" in the term 2pq is necessary because _____.
heterozygotes can come about in two ways
A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because _____.
natural selection is generally limited to modifying structures that were present in previous generations and in previous species