Evolution

Question 1

Q: How much do two randomly selected humans differ genetically, and how does this compare to other species?

Answer 1

A: Two randomly selected humans differ by only one DNA base per thousand (99.9% identical). In comparison, fruit flies differ by 10 bases per thousand, and Adélie penguins are 2-3 times more genetically variable than humans.

Question 2

Q: What is population genetics, and what does it study?

Answer 2

A: Population genetics is the study of genetic variation within natural populations, focusing on how alleles in a population’s gene pool are distributed and change over time. It looks at how genetic diversity influences evolution and adaptation.

Question 3

3. Q: What is a gene pool, and what does it include?

Answer 3

A: A gene pool contains all the alleles present in the individuals of a species. It includes alleles responsible for traits like hair color, eye color, skin color, and other characteristics that vary between individuals.

Question 4

4. Q: What are the two main sources of genetic variation in populations?

Answer 4

The two main sources of genetic variation are mutation and recombination. Mutations create new alleles, while recombination shuffles existing alleles to create new combinations during sexual reproduction.

Question 5

5. Q: How do somatic mutations differ from germ-line mutations?

Answer 5

Somatic mutations occur in non-reproductive cells and affect only the individual, meaning they are not passed on to offspring. Germ-line mutations occur in reproductive cells (sperm or eggs) and can be inherited by the next generation, potentially contributing to evolutionary changes.

Question 6

Q: What are the different types of mutations that can occur, and what are their effects?

Answer 6

A: Mutations can be neutral (having no effect), deleterious (harmful to survival or reproduction), or advantageous (improving survival or reproduction). Advantageous mutations may increase in frequency within a population over time through natural selection.

Question 7

7. Q: Why is recombination critical for generating genetic variation in a population?

Answer 7

A: Recombination is important because it reshuffles existing alleles into new combinations, generating genetic diversity. This process creates new allele permutations that natural selection can act on, driving evolutionary changes and helping populations adapt to their environments.

Question 8

8. Q: What role do mutations play in genetic variation?

Answer 8

Mutations introduce new alleles into a population’s gene pool. Some mutations are neutral, others harmful, and a few beneficial. These variations can accumulate over time, providing raw material for evolution and allowing populations to adapt to changing conditions.

Question 9

9. Q: How do mutation and recombination together contribute to genetic diversity?

Answer 9

A: Mutations create new alleles by changing the DNA sequence, while recombination during meiosis shuffles these new and existing alleles into different combinations. Together, they generate a wide variety of genetic combinations that enhance the adaptability and evolution of species.

Question 10

10. Q: What happens to advantageous mutations in a population over time?

Answer 10

A: Advantageous mutations improve an organism’s chances of survival and reproduction. Over time, these mutations can increase in frequency within the population, potentially becoming common across the species as they help individuals better adapt to their environment.

Question 11

1. Q: What is allele frequency, and how is it calculated in a population?

Answer 11

A: Allele frequency is the proportion of a specific allele relative to the total number of alleles for that gene in a population. It is calculated by dividing the number of copies of the allele of interest by the total number of alleles for that gene in the population. For example, in a population of pea plants, if there are 100 plants, each having two alleles for a particular gene, there are 200 total alleles. If 50 plants are homozygous recessive (aa), 25 are heterozygous (Aa), and 25 are homozygous dominant (AA), the allele frequency for “a” would be calculated by counting all the “a” alleles (50 from “aa” and 25 from “Aa”) and dividing by the total number of alleles (200). The result would be 75/200 = 37.5%.

Question 12

2. Q: What is genotype frequency, and how does it differ from allele frequency?

Answer 12

A: Genotype frequency refers to the proportion of individuals in a population that carry a particular genotype (e.g., AA, Aa, or aa for a diploid organism). It is calculated by dividing the number of individuals with a specific genotype by the total population. Allele frequency, on the other hand, looks at the proportion of specific alleles across all individuals in the population. While genotype frequency focuses on the distribution of genetic combinations (AA, Aa, aa), allele frequency examines the overall abundance of each individual allele (A or a) regardless of their combinations.

Question 13

Q: In a population of 100 pea plants with genotype frequencies of 50 aa, 25 Aa, and 25 AA, how do you calculate the allele frequency of “A” and “a”?

Answer 13

A: To calculate allele frequencies:
* For “a”: There are 50 “aa” plants (each contributing 2 “a” alleles) and 25 “Aa” plants (each contributing 1 “a” allele). Therefore, the number of “a” alleles is (50 x 2) + (25 x 1) = 100 + 25 = 125.
* For “A”: There are 25 “AA” plants (each contributing 2 “A” alleles) and 25 “Aa” plants (each contributing 1 “A” allele). Therefore, the number of “A” alleles is (25 x 2) + (25 x 1) = 50 + 25 = 75.
* The total number of alleles is 100 plants x 2 alleles per plant = 200 alleles.
* Allele frequency of “a” = 125/200 = 62.5%.
* Allele frequency of “A” = 75/200 = 37.5%.

Question 14

4. Q: What is the importance of allele frequencies in population genetics, and how do they relate to genetic variation?

Answer 14

A: Allele frequencies are critical in population genetics because they provide insight into the genetic composition of a population and help determine the level of genetic diversity. High allele frequency variation within a population indicates greater genetic diversity, which is essential for the adaptability and survival of a species. Changes in allele frequencies over generations are a direct measure of evolutionary forces like natural selection, genetic drift, mutation, and gene flow acting on the population.

Question 15

5. Q: What early methods were used by geneticists to measure genetic variation, and why were they limited?

Answer 15

A: Early population geneticists relied on observable traits (phenotypes) and methods like gel electrophoresis to measure genetic variation. Observable traits, such as flower color or blood type, were used to infer genetic differences among individuals. However, this approach was limited because many traits are controlled by multiple genes, making it difficult to determine the underlying genetic variation accurately. Additionally, traits influenced by both genetic and environmental factors were harder to analyze using just phenotypic observation.

Question 16

6. Q: What is the ABO blood group system, and how is it used to study genetic variation?

Answer 16

A: The ABO blood group system is determined by a single gene with three alleles (A, B, O). These alleles combine to produce four blood types (A, B, AB, O) and six genotypes:
* Blood type A: Genotypes AA or AO.
* Blood type B: Genotypes BB or BO.
* Blood type AB: Genotype AB.
* Blood type O: Genotype OO.
Since this trait is controlled by a single gene, it provides a simple and clear example of genetic variation in a population. Blood type is a readily observable and measurable trait that has been widely used in genetics studies.

Question 17

7. Q: How are complex traits like skin color different from simple traits like blood type when measuring genetic variation?

Answer 17

A: Complex traits, such as skin color, are controlled by multiple genes and are influenced by environmental factors, making it more difficult to measure genetic variation and predict phenotypes based on genotypes. For instance, human skin color is influenced by many different genes and can vary significantly depending on factors such as sun exposure. In contrast, simple traits, like blood type, are controlled by a single gene with well-defined alleles, making it easier to link specific genotypes to observable traits.

Question 18

8. Q: How does genetic variation in a population affect evolutionary processes?

Answer 18

A: Genetic variation within a population provides the raw material for evolution. Populations with higher genetic diversity are more likely to adapt to environmental changes, as some individuals may carry alleles that confer a survival advantage. Evolutionary processes such as natural selection, genetic drift, and gene flow act on this genetic variation, altering allele frequencies over time. The presence of advantageous alleles may increase in a population, while deleterious alleles may decrease, driving the population’s evolution.

Question 19

9. Q: How do environmental factors and genetic factors work together to influence complex traits?

Answer 19

A: Complex traits are influenced by both genetic factors (multiple genes contributing to the trait) and environmental factors (external conditions such as diet, climate, and lifestyle). For example, human height is determined by several genes, but factors like nutrition during childhood also play a significant role. Similarly, skin color is affected by both genetic makeup and environmental factors like sun exposure. This interaction between genes and the environment makes it challenging to predict complex traits based solely on genetic information.

Question 20

1. Q: What is protein gel electrophoresis, and how does it measure genetic variation?

Answer 20

A: Protein gel electrophoresis separates segments of DNA or proteins by size using an electrical charge applied to a gel. This technique can detect genetic variation by showing distinct bands for different alleles based on their charge and size. Heterozygous individuals for a mutation that changes an amino acid will show two bands, indicating the presence of both alleles

Question 21

2. Q: What are the limitations of protein gel electrophoresis in detecting genetic variation?

Answer 21

A: Protein gel electrophoresis can only detect mutations that alter a protein’s mobility in the gel, which is a result of amino acid changes. It cannot detect silent mutations that change DNA sequences but do not affect the encoded amino acid. This limits its ability to comprehensively measure genetic variation.

Question 22

3. Q: Why is DNA sequencing considered the gold standard for measuring genetic variation?

Answer 22

A: DNA sequencing allows for the detection of all types of genetic variation, including silent mutations that protein gel electrophoresis cannot detect. By analyzing differences in the DNA sequence, such as a change from A to G at a specific nucleotide position, researchers can obtain a complete picture of genetic variation in a population.

Question 23

4. Q: How are allele frequencies calculated using DNA sequencing?

Answer 23

A: Allele frequencies are calculated by sequencing a population sample and counting how often a specific mutation occurs. For example, in a sample of 50 individuals, each with two copies of a gene, the total number of sequences is 100. If 70 sequences show “A” and 30 show “G,” the allele frequency of “A” is 0.7 (70/100), and the frequency of “G” is 0.3 (30/100).

Question 24

5. Q: What are polymorphisms, and how are they detected?

Answer 24

A: Polymorphisms are variations in the DNA sequence that occur at a specific nucleotide position in different individuals of a population. They are detected through DNA sequencing, which identifies the multiple forms (alleles) of a gene present in the population.

Question 25

6. Q: What does it mean for an allele to be “fixed” in a population?

Answer 25

A: An allele is “fixed” when it is the only allele present for a particular gene in the population, meaning its frequency is 1 (or 100%). This indicates that all individuals in the population have the same allele for that gene.

Question 26

7. Q: Why was genetic variation difficult to measure before the advent of molecular tools like DNA sequencing?

Answer 26

A: Before DNA sequencing, genetic variation was difficult to measure because observable traits (phenotypes) often did not directly correspond to genetic differences. Many traits are influenced by multiple genes, making it hard to trace phenotypic variation back to genetic variation. Techniques like gel electrophoresis helped, but they were limited to detecting only certain types of genetic changes.

Question 27

8. Q: How has DNA sequencing revealed more genetic variation in natural populations compared to previous methods like protein gel electrophoresis?

Answer 27

A: DNA sequencing has revealed more genetic variation because it detects silent mutations and other nucleotide changes that do not affect the protein’s amino acid sequence. Previous methods, like protein gel electrophoresis, only detected mutations that altered protein mobility. DNA sequencing provides a more comprehensive view of genetic diversity by identifying all genetic changes, even those that do not result in phenotypic differences.

Question 28

9. Q: How would you calculate the frequency of an allele in a population of 500 individuals if 800 sequences have “G” and 200 sequences have “T”?

Answer 28

A: In a population of 500 diploid individuals, there are 1000 total sequences (500 x 2). If 800 sequences have “G” and 200 sequences have “T,” the frequency of the “T” allele is 200/1000 = 0.2 (or 20%).`

Question 29

1. Q: What is evolution at the genetic level?

Answer 29

A: Evolution is a change in the frequency of an allele or a genotype from one generation to the next. For example, if there are 200 copies of an allele in one generation and 300 copies in the next, evolution has occurred. Evolution can also happen without changes in allele frequency if the frequencies of genotypes (like AA, AG, GG) change.

Question 30

2. Q: What is the Hardy-Weinberg equilibrium, and what does it describe?

Answer 30

A: The Hardy-Weinberg equilibrium describes a situation where allele and genotype frequencies remain constant in a population over time if no evolutionary forces (like natural selection or genetic drift) are acting on the population. In essence, it defines conditions under which evolution does not occur.

Question 31

3. Q: What are the five conditions that must be met for a population to be in Hardy-Weinberg equilibrium?

Answer 31

A: The five conditions are:
1. No difference in survival or reproductive success between genotypes.
2. Large population size to prevent random changes (genetic drift).
3. No migration into or out of the population.
4. No mutations.
5. Random mating, where individuals do not choose mates based on genotype.

Question 32

4. Q: How can evolution occur without changes in allele frequency?

Answer 32

A: Evolution can occur without changes in allele frequency if genotype frequencies change. For example, even if the frequency of the “A” and “G” alleles remains the same from one generation to the next, changes in the proportions of the AA, AG, and GG genotypes can still be considered evolution.

Question 33

5. Q: How does the size of a population affect Hardy-Weinberg equilibrium?

Answer 33

A: Population size is critical for maintaining Hardy-Weinberg equilibrium. In large populations, allele frequencies are stable because random events have less impact. In small populations, random changes in allele frequency (genetic drift) can occur, causing the population to deviate from equilibrium.

Question 34

6. Q: What happens to Hardy-Weinberg equilibrium if individuals migrate into or out of a population?

Answer 34

A: Migration disrupts Hardy-Weinberg equilibrium by introducing new alleles into the population or removing alleles from it. This alters allele frequencies and may lead to evolutionary changes

Question 35

7. Q: Why is random mating important for Hardy-Weinberg equilibrium?

Answer 35

A: Random mating ensures that individuals in a population do not select mates based on genotype. If mating is non-random (for example, AA individuals preferentially mating with AA), it changes genotype frequencies, which disrupts Hardy-Weinberg equilibrium. However, allele frequencies might remain unaffected.

Question 36

8. Q: What does it mean when a population departs from Hardy-Weinberg equilibrium?

Answer 36

A: A departure from Hardy-Weinberg equilibrium means that one or more of the conditions (such as random mating or large population size) are not being met. This implies that evolutionary forces like natural selection, mutation, migration, or genetic drift are acting on the population.

Question 37

9. Q: How can you use Hardy-Weinberg equilibrium to determine if evolution is occurring?

Answer 37

A: By comparing the observed genotype frequencies in a population to the frequencies predicted by Hardy-Weinberg equilibrium, you can detect whether evolutionary forces are at work. If the observed frequencies match the predicted ones, the population is in equilibrium, and no evolution is occurring. If they differ, it indicates that evolution is happening.

Question 38

1. Q: What is natural selection, and how does it affect allele frequencies?

Answer 38

A: Natural selection is the process by which individuals with certain heritable traits survive and reproduce more successfully than others. Over time, natural selection increases the frequency of alleles that contribute to advantageous traits, causing the population to evolve. It acts on phenotypes (observable traits), but the underlying result is a change in allele frequencies.

Question 39

2. Q: What are the three types of natural selection, and how do they differ?

Answer 39

A: The three types of natural selection are:
* Directional selection: Favors individuals at one extreme end of the trait spectrum, leading to a shift in the population’s trait distribution.
* Stabilizing selection: Favors individuals with intermediate traits, reducing variation and maintaining the status quo.
* Disruptive selection: Favors individuals at both extremes of the trait spectrum, which can lead to two distinct forms in the population.

Question 40

3. Q: What is genetic drift, and how does it differ from natural selection?

Answer 40

A: Genetic drift is a random process that changes allele frequencies in small populations. Unlike natural selection, which is non-random and driven by survival advantages, genetic drift occurs due to chance events, such as random deaths or births. It can result in the loss of genetic variation and even lead to the fixation or elimination of alleles.

Question 41

4. Q: What are the founder effect and bottleneck effect in genetic drift?

Answer 41

A: The founder effect occurs when a small group of individuals colonizes a new area, and the allele frequencies in this new population differ from the original population. The bottleneck effect happens when a population’s size is drastically reduced by an event (e.g., a natural disaster), leading to a change in allele frequencies due to the small surviving population.

Question 42

6. Q: Why are mutations important in the process of evolution?

Answer 42

A: Mutations introduce new alleles into a population, creating genetic variation. While most mutations are neutral or harmful, some mutations can provide a survival advantage. Without mutations, evolution would not have the genetic variation necessary to act upon.

Question 43

5. Q: What is gene flow, and how does it affect genetic variation?

Answer 43

A: Gene flow is the movement of alleles between populations, usually due to migration. It increases genetic diversity by introducing new alleles into a population and can prevent populations from becoming too genetically distinct by maintaining some genetic similarity.

Question 44

7. Q: What is balancing selection, and how does it maintain genetic diversity?

Answer 44

A: Balancing selection maintains multiple alleles in a population. A common example is heterozygote advantage, where individuals with two different alleles (heterozygous) have a survival advantage over those with two identical alleles (homozygous). This prevents any single allele from becoming fixed and maintains genetic diversity.

Question 45

8. Q: How do the processes of natural selection and genetic drift differ in small versus large populations?

Answer 45

A: In small populations, genetic drift plays a larger role because chance events can have a significant impact on allele frequencies. In large populations, natural selection is the dominant force shaping allele frequencies, as advantageous traits are more likely to spread through the population, while genetic drift has less of an effect due to the large number of individuals.

Question 46

9. Q: What happens when a population experiences gene flow?

Answer 46

A: When gene flow occurs, alleles move between populations through migration, introducing new alleles or changing existing allele frequencies. This process increases genetic diversity in the receiving population and helps maintain genetic similarity between populations.

Question 47

Q: What is the Hardy-Weinberg equilibrium, and why is it important for population genetics?

Answer 47

A: The Hardy-Weinberg equilibrium describes a situation where allele and genotype frequencies remain constant across generations unless evolutionary forces act upon the population. It serves as a starting point for genetic analysis by providing a baseline model for studying evolution. When a population deviates from this equilibrium, it indicates that evolutionary processes, such as selection or genetic drift, are at work.

Question 48

Q: Why is it significant when a population deviates from Hardy-Weinberg equilibrium?

Answer 48

A deviation from Hardy-Weinberg equilibrium means that evolution is occurring within the population. It indicates that allele or genotype frequencies are changing due to one or more evolutionary mechanisms, such as natural selection, genetic drift, migration, mutation, or nonrandom mating. Studying these deviations helps identify which forces are driving evolutionary change.

Question 49

3. Q: How does Hardy-Weinberg equilibrium help in detecting evolutionary changes?

Answer 49

A: Hardy-Weinberg equilibrium provides a baseline to measure genetic stability in a population. When allele or genotype frequencies differ from predictions made by the Hardy-Weinberg equation, it indicates that evolutionary forces are acting on the population. Researchers can then investigate whether these changes are due to mechanisms like natural selection, genetic drift, or gene flow.

Question 50

4. Q: What are the five mechanisms that can cause a population to deviate from Hardy-Weinberg equilibrium?

Answer 50

A: The five mechanisms that can cause deviations from Hardy-Weinberg equilibrium are:
1. Selection: Certain alleles offer a survival advantage, increasing their frequency in the population.
2. Genetic Drift: Random events cause changes in allele frequencies, especially in small populations.
3. Migration (Gene Flow): Movement of individuals into or out of a population changes allele frequencies.
4. Mutation: New alleles are introduced into the population.
5. Nonrandom Mating: Individuals preferentially mate with others of certain genotypes, altering genotype frequencies.

Question 51

5. Q: Can evolution occur without changes in allele frequencies? If so, how?

Answer 51

A: Yes, evolution can occur without changes in allele frequencies if genotype frequencies change. For example, nonrandom mating can cause certain genotypes to become more common without altering the underlying allele frequencies. This is still considered evolution because the population’s genetic structure is changing over time.

Question 52

6. Q: How do you calculate genotype frequencies using the Hardy-Weinberg equation?

Answer 52

A: Genotype frequencies can be calculated using the Hardy-Weinberg equation: p^2 + 2pq + q^2 = 1 , where:
* p^2 represents the frequency of homozygous dominant individuals.
* q^2 represents the frequency of homozygous recessive individuals.
* 2pq represents the frequency of heterozygous individuals.
For example, in a population where p = 0.6 and q = 0.4 , the genotype frequencies are:
* Homozygous dominant (AA): p^2 = 0.36 (36%)
* Homozygous recessive (aa): q^2 = 0.16 (16%)
* Heterozygous (Aa): 2pq = 0.48 (48%)

Question 53

Q: What can we conclude about a population whose allele frequencies are not in Hardy-Weinberg equilibrium?

Answer 53

A: If a population’s allele frequencies are not in Hardy-Weinberg equilibrium, we can conclude that the population is evolving. However, this does not tell us which evolutionary mechanism (such as selection, genetic drift, or migration) is causing the change. More detailed genetic analysis is required to determine the specific forces at work.

Question 54

1. Q: What is genetic drift, and how does it differ from natural selection?

Answer 54

A: Genetic drift is the random change in allele frequencies from generation to generation due to chance, not because of any selective pressure. Unlike natural selection, which favors traits that improve survival and reproduction, genetic drift can cause alleles to increase or decrease in frequency simply by random events, especially in small populations.

Question 55

2. Q: How does genetic drift affect small populations compared to large populations?

Answer 55

A: Genetic drift has a much larger effect on small populations. In small populations, allele frequencies can change drastically due to random events, potentially leading to the fixation or loss of alleles in just a few generations. In larger populations, genetic drift has less influence because random fluctuations are averaged out over more individuals.

Question 56

3. Q: What is a population bottleneck, and how does it lead to genetic drift?

Answer 56

A: A population bottleneck occurs when a large population is drastically reduced in size, often due to an environmental disaster or other events. The small number of survivors carry only a fraction of the original population’s genetic diversity, leading to genetic drift as allele frequencies change randomly among the few remaining individuals.

Question 57

4. Q: What is the founder effect, and how does it relate to genetic drift?

Answer 57

A: The founder effect occurs when a small group of individuals establishes a new population in a different area. This new population often has reduced genetic variation compared to the original population, and genetic drift can cause random changes in allele frequencies due to the small number of individuals involved.

Question 58

5. Q: How can a neutral mutation become fixed in a population through genetic drift?

Answer 58

A: A neutral mutation does not affect an individual’s fitness, so it is not influenced by natural selection. However, if individuals carrying the mutation reproduce, the mutation may randomly increase in frequency due to genetic drift. Over time, if genetic drift continues, the neutral mutation may become fixed in the population, meaning it is present in all individuals.

Question 59

6. Q: Why does genetic drift have a stronger effect in small populations?

Answer 59

A: In small populations, the impact of random events is magnified. A few individuals may carry rare alleles, and if they fail to reproduce, those alleles can be lost entirely. Similarly, if a few individuals carrying a rare allele reproduce more, the allele can increase in frequency rapidly. This makes genetic drift more pronounced in small populations, where chance plays a bigger role.

Question 60

7. Q: What are population bottlenecks and founder events, and how do they contribute to genetic drift?

Answer 60

A: Population bottlenecks occur when a large population is reduced to a small number, leading to reduced genetic diversity and random changes in allele frequencies. Founder events occur when a small number of individuals establish a new population, often leading to genetic drift as allele frequencies in the new population may differ significantly from the original population. Both processes contribute to genetic drift by reducing genetic variation and allowing chance to play a larger role in determining allele frequencies.

Question 61

8. Q: How does genetic drift lead to the fixation or loss of alleles in a population?

Answer 61

A: Genetic drift can cause alleles to become fixed (present in all individuals) or lost (completely absent) in a population, especially in small populations. Due to random chance, certain alleles may be passed on more frequently, while others are passed on less, eventually leading to the fixation or elimination of those alleles over time.

Question 62

9. Q: How do simulations of genetic drift demonstrate its effect on different population sizes?

Answer 62

A: Simulations of genetic drift show that in very small populations (like those of four individuals), alleles either become fixed or are lost in a few generations due to random chance. In larger populations, genetic drift is less dramatic because random fluctuations are less likely to have such extreme effects. In large populations, alleles are more likely to maintain intermediate frequencies over time.

Question 63

1. Q: What is migration in evolutionary terms, and how does it affect genetic variation between populations?

Answer 63

A: Migration is the movement of individuals from one population to another, resulting in gene flow. This movement of alleles between populations leads to the homogenization of allele frequencies, reducing genetic differences between populations over time.

Question 64

2. Q: How does mutation contribute to genetic variation?

Answer 64

A: Mutation introduces new alleles into a population, creating genetic diversity. While mutations are rare and often have little short-term impact, they are crucial for evolution as they provide the raw material for natural selection and other evolutionary forces to act on.

Question 65

3. Q: What is nonrandom mating, and how does it affect genotype frequencies without altering allele frequencies?

Answer 65

A: Nonrandom mating occurs when individuals choose mates based on specific traits or genotypes, rather than mating randomly. This alters the genotype frequencies, often increasing homozygosity (as in the case of inbreeding) or heterozygosity, depending on the mating patterns. However, it does not directly change allele frequencies.

Question 66

4. Q: What is inbreeding, and how does it lead to inbreeding depression?

Answer 66

A: Inbreeding occurs when individuals mate with close relatives, leading to an increase in homozygous genotypes and a decrease in heterozygosity. If deleterious recessive alleles are present, inbreeding can result in inbreeding depression, where offspring suffer from reduced fitness due to the increased likelihood of inheriting harmful alleles.

Question 67

5. Q: How did inbreeding depression affect the Florida panther, and what was done to address it?

Answer 67

A: Inbreeding depression caused a decline in the fitness of the Florida panther population due to the accumulation of deleterious recessive alleles. To mitigate this, conservation efforts introduced new genetic material from other populations, which helped restore genetic diversity and halt the population’s decline.

Question 68

6. Q: What is genetic drift, and how does it affect small populations?

Answer 68

A: Genetic drift is the random fluctuation of allele frequencies in a population, particularly strong in small populations. These random changes can lead to the fixation or loss of alleles over time, especially when population sizes are small, as chance plays a larger role in determining which alleles are passed on to the next generation.

Question 69

7. Q: How does genetic drift differ from selection?

Answer 69

A: While selection acts on traits that increase fitness, genetic drift changes allele frequencies purely by chance. Selection increases the frequency of advantageous traits, while genetic drift can cause random changes, including the fixation or loss of alleles, without regard to fitness.

Question 70

8. Q: How does nonrandom mating, specifically inbreeding, alter genotype frequencies in a population?

Answer 70

A: Inbreeding increases the frequency of homozygous genotypes while reducing the frequency of heterozygous genotypes. Although allele frequencies remain unchanged, the shift toward homozygosity can increase the probability of deleterious recessive alleles being expressed, leading to inbreeding depression.

Question 71

. Q: What are the key impacts of selection, genetic drift, migration, mutation, and nonrandom mating as outlined in Table 20.2?

Answer 71

A:
* Selection: Alters allele frequencies based on fitness advantages, leading to adaptation.
* Genetic Drift: Causes random changes in allele frequencies, particularly in small populations.
* Migration: Homogenizes allele frequencies between populations.
* Mutation: Introduces new alleles, providing genetic variation for evolution.
* Nonrandom Mating (Inbreeding): Increases homozygosity and can lead to a loss of heterozygotes without changing allele frequencies.

Question 72

Q: Why is selection the only evolutionary mechanism that can result in adaptation?

Answer 72

A: Selection is the only evolutionary mechanism that can lead to adaptation because it directly favors traits that improve an organism’s fitness—its ability to survive and reproduce. While other mechanisms like genetic drift, mutation, and migration can change allele frequencies randomly, selection consistently promotes beneficial traits, increasing their frequency in a population. Over time, this process leads to populations becoming better suited to their environment, as individuals with advantageous traits are more likely to survive and pass those traits to their offspring.

Question 73

A female lizard flower on a go to an island where they lays previously fertilizes eggs and starts a new population on the island where there are no other lizards. How do you think the genetic variation and allele frequency of the island population will be compared to those of the mainland population? Which mechanism of evolution is at work here?

Answer 73

When a female lizard establishes a new population on an island by laying her fertilized eggs, the genetic variation of the island population is expected to be lower than that of the mainland population. Since the island population starts with just one individual and her offspring, the genetic diversity is limited to the alleles she carries. Over time, this population will be subject to genetic drift, a mechanism of evolution that causes random fluctuations in allele frequencies, particularly in small populations. In this case, a founder event is at work, which occurs when a small group of individuals establishes a new population. This event leads to allele frequencies that may be quite different from those in the larger mainland population. As the population grows, genetic drift can lead to the fixation or loss of certain alleles, reducing genetic diversity and making the island population genetically distinct from the mainland population.

Question 74

Q: What is a molecular clock, and how is it used in evolutionary studies?

Answer 74

A: A molecular clock is a region of DNA or protein that accumulates mutations at a consistent rate over time. It is used to estimate the divergence time between species by comparing the number of genetic differences and calibrating this with fossil record data. The longer two species have been separated, the more mutations are expected to accumulate.

Question 75

Q: Why do we expect a protein’s rate of molecular evolution to be correlated with its function?

Answer 75

A: The molecular clocks of different proteins “tick” at different rates depending on the strength of negative selection against mutations. Proteins with critical functions, such as histones, evolve very slowly because any mutations can be harmful. On the other hand, pseudogenes, which no longer serve a function, evolve rapidly as all mutations are neutral.

Question 76

Q: What is the molecular clock of histone proteins, and why is it slow?

Answer 76

A: Histones, which wrap DNA into chromatin, have one of the slowest molecular clocks. Their structure is so essential that any mutation can disrupt their function, leading to strong negative selection that eliminates harmful mutations. As a result, histone proteins have hardly changed in over 2 billion years of evolution.

Question 77

Q: How do pseudogenes evolve, and how is their molecular clock different from functional genes?

Answer 77

A: Pseudogenes are non-functional genes that evolve rapidly because all mutations in them are neutral. Since there is no function to preserve, mutations accumulate without negative selection acting against them, making their molecular clock tick faster than that of functional genes.

Question 78

Q: How do fossil records help set a molecular clock?

Answer 78

A: Fossil records provide the chronological data needed to calibrate molecular clocks. For example, a 1967 study by Sarich and Wilson used fossil evidence to estimate that humans and chimpanzees diverged around 6 million years ago, allowing them to set the clock for calculating genetic divergence rates between species.

Question 79

Q: What is molecular evolution, and how does it lead to species divergence?

Answer 79

A: Molecular evolution refers to the accumulation of genetic differences over generations. As mutations arise and are fixed in populations, species gradually diverge genetically. Over time, populations become so genetically distinct that they are considered different species, and this process is tracked using the molecular clock.