Question 1

Certain small towns in the western United States have remained isolated and inbred since their settlement many years ago.Some alleles are more common in these communities as compared to the rest of the population.This effect is known as

Accepted Answer

The effect described is known as the founder principle, which occurs when a small group of individuals establishes a new population and their genetic makeup becomes more pronounced due to genetic drift. This can result in certain alleles being more common in the isolated population compared to the larger population from which they originated.

Question 2

The type of non-random mating that causes the frequencies of particular genotypes to differ greatly from those predicted by the Hardy-Weinberg equilibrium is called

Accepted Answer

Assortative mating occurs when individuals choose partners based on similar characteristics, such as genotype. This causes an excess of homozygous individuals and a deficiency of heterozygous individuals, altering the frequencies of genotypes from what is expected under Hardy-Weinberg equilibrium.

Question 3

Gene flow,defined as the movement of genes from one population to another,can take place by migration,as well as

Accepted Answer

Hybridization between individuals of adjacent populations can result in gene flow. This occurs when individuals from two different populations breed and produce hybrids that have a mixture of genes from both populations. Over time, if these hybrids continue to breed with individuals from both populations, the genes from the two populations will become more mixed, leading to gene flow. Migration (A) can also lead to gene flow, but it specifically refers to the physical movement of individuals from one population to another, rather than the mixing of genes through hybridization. Mating with certain trait-containing individuals (B) may increase the frequency of certain genes in a population, but it does not necessarily lead to gene flow between two populations. Removing barriers between populations (D) could potentially lead to an increase in gene flow, but this would depend on whether individuals from the two populations are able to breed and produce viable offspring. The physical movement of genes within an individual by transposons (E) does not result in gene flow between populations.

Question 4

Which one of the following is not an agent of natural evolutionary change?

Accepted Answer

Artificial selection is not an agent of natural evolutionary change because it is a process in which humans intentionally select and breed organisms with desirable traits. It is not a natural process, but rather a result of human intervention. The other options (mutation, migration, genetic drift, and non-random mating) are all natural processes that can drive evolutionary change in populations over time.

Question 5

In order for natural selection to occur within a population,certain conditions must be met.One such condition is

Accepted Answer

Phenotypic variations that are genetic are necessary for natural selection to occur because natural selection acts on heritable traits. If there are no genetic differences among individuals in a population, then there is no variation for natural selection to act upon. Therefore, phenotypic variations that are genetic are a key condition for natural selection to occur.

Question 6

The phenomenon in which rare alleles become more common in new populations is called

Accepted Answer

The founder effect occurs when a small group of individuals becomes isolated from a larger population, leading to a gene pool that is not representative of the original population. This often results in an increase in the frequency of rare alleles.

Question 7

In some populations the drive is to mate with individuals that are phenotypically different at a variety of loci.This leads to large numbers of heterozygotes and is called

Accepted Answer

Disassortative mating refers to the preference for individuals that are phenotypically different at a variety of loci, which promotes outbreeding and leads to larger numbers of heterozygotes. Neutral theory, shifting balance theory, bottleneck effect, and founder effect are all different mechanisms that can affect genetic variation in populations but are not specifically related to mate choice based on phenotypic differences.

Question 8

Sometimes a restriction in genetic variability is imposed on populations by natural catastrophes such as flooding,earthquake,etc.The surviving individuals reflect only a small,random genetic sample of the population affected.This process is termed

Accepted Answer

The process described in the question refers to the bottleneck effect, which occurs when a population undergoes a drastic and sudden reduction in size, resulting in a small and random sample of the original gene pool being represented in the surviving population. This can lead to reduced genetic diversity and potentially harmful genetic effects. Mutation refers to changes in an individual's genetic information, while migration involves the movement of individuals between populations. Genetic drift is a general term used to describe random fluctuations in gene frequency within a population, while assortative mating refers to non-random mating based on certain traits.

Question 9

Which one of the following is not an agent of evolutionary change?

Accepted Answer

Random mating does not directly introduce or eliminate new genetic variation, nor does it disproportionately favor certain genotypes over others. Therefore, it is not an agent of evolutionary change. However, random mating is a genetic assumption often made in population genetics models to simplify calculations and make predictions about evolution.

Question 10

In small populations,frequencies of certain alleles may change by chance alone.Such random change in the frequency of alleles is called

Accepted Answer

The random change in the frequency of alleles in a small population is called genetic drift. This is due to chance events like random deaths, births or migrations, which may result in some alleles becoming more or less common. This is different from mutation, which is a random change in the genetic code, or selection, which is the process by which certain traits are favored or disfavored based on their effect on survival or reproduction. Migration and nonrandom mating also play a role in changing allele frequency, but are not specific to small populations.

Question 11

Compared with Hardy-Weinberg predictions,populations that have practiced assortative mating have

Accepted Answer

Assortative mating is the tendency of individuals to mate with others who are similar in phenotype or genotype. This can lead to an increase in homozygosity within the population, as individuals with the same genotype are more likely to mate and produce offspring with the same genotype. This is in contrast to the Hardy-Weinberg equilibrium, which predicts a stable frequency of genotypes over time with equal amounts of heterozygotes and homozygotes. Therefore, populations that practice assortative mating would have more homozygotes than expected under Hardy-Weinberg equilibrium.

Question 12

When selection acts to eliminate one extreme from an array of phenotypes it is called

Accepted Answer

Directional selection occurs when selection pressures favor one extreme phenotype over others, leading to a shift in the population's trait distribution.

Question 13

Although it was a rare trait in the mainland population,one of the original female mice is homozygous for very large ears.This will lead to a population with a higher incidence of big ears than the mainland population because of

Accepted Answer

The founder effect occurs when a small group of individuals establish a new population that is genetically distinct from the original population. In this case, the original female mouse with the trait for large ears is the founder individual for the new population. As a result, the frequency of the large ear trait will be higher in the new population due to the founder effect.

Question 14

The Hardy-Weinberg equilibrium conditions for populations of organisms result in

Accepted Answer

The conditions of the Hardy-Weinberg equilibrium (random mating, large population size, no mutation, no migration, and no natural selection) ensure that the frequencies of alleles and genotypes in a population do not change over time. Therefore, the population remains in equilibrium, and there are no evolutionary changes.

Question 15

Populations of humans are known to have founder effects.For instance there are small populations in the US that frequently show

Accepted Answer

Founder effects can lead to certain traits, such as polydactyly (having extra fingers), being more common in small, isolated populations due to the limited genetic diversity.

Question 16

Hardy-Weinberg pointed out that the original proportions of the genotypes in a population would remain constant from generation to generation if certain assumptions are met.Which one of the following is not a Hardy-Weinberg condition?

Accepted Answer

The presence of polymorphic loci (i.e. having more than one allele at a particular gene locus) is not a condition of Hardy-Weinberg equilibrium. In fact, the Hardy-Weinberg model can be used to calculate the frequency of alleles and genotypes in a population even when there is genetic variation present.

Question 17

For a gene with two alternative alleles,a (frequency p)and a (frequency q),the term in the algebraic form of the Hardy-Weinberg equilibrium for the heterozygote genotype frequency is

Accepted Answer

The Hardy-Weinberg equilibrium equation for the heterozygote genotype frequency is given by 2pq, where p is the frequency of the dominant allele (a) and q is the frequency of the recessive allele (a). This equation represents the expected frequency of heterozygotes in a population under the assumption of random mating and no other evolutionary processes. Thus, the correct answer is C, which represents the Hardy-Weinberg equilibrium equation for the heterozygote genotype frequency.

Question 18

About 80% of the alleles present in thoroughbred horses can be dated back to 31 known ancestors from the late eighteenth century.As a result,one would expect

Accepted Answer

Since such a large proportion of alleles among thoroughbred horses can be traced back to a limited number of ancestors, there is likely to be little variation in their physiology and behavior.

Question 19

Cheetahs have been through a genetic bottleneck;evidence for this is that

Accepted Answer

A genetic bottleneck occurs when a large population is reduced to a small population, leading to a loss of genetic variability. Cheetahs have been through a genetic bottleneck, resulting in very little genetic variability among individuals.

Question 20

The total of all the alleles of all the genes in a population can be thought of as

Accepted Answer

The term "gene pool" refers to the total collection of all the alleles of all the genes in a population. It represents the genetic diversity of a population and is important in understanding the potential for evolution to occur.

Quiz 20: Genes Within Populations