Chapter 26
What is required for gene flow to occur.
- Individuals must migrate from one population to another - Migrants must be fertile and pass their genes to the next generation
What are the two most important consequences of the founder effect on the newly founded population.
- The founding population typically has less genetic diversity than the original population - The founding population typically has very different allele frequencies from those of the original population
In a population of frogs, a gene is found in two forms- D, and d. The numbers of individuals with different genotypes for that gene are 30 (DD), 18 (Dd), and 12 (dd). What is the frequency of the heterozygous genotype?
0.30
A gene is found in two forms in a population of plants. The two alleles are denoted as B, and b. You determine that the frequency of the B allele in this population is 0.2. If this population was in a Hardy-Weinberg equilibrium, calculate the probability of a heterozygote in the next generation.
0.32
Consider a population, in which a gene is present in the form of two alleles with the following frequencies:A-0.4 and a- 0.6. The value of f (how much genotype frequencies deviate from Hardy-Weinberg equilibrium due to non-random mating) for this population is 0.3. What would the predicted frequency of heterozygotes be in this population?
0.34
Consider a gene, which is found in two forms in a population: D and d, with frequencies of 0.6 and 0.4 respectively. The D allele can mutate into the d allele at a rate of 0.00001 mutations per gene per generation. What would the expected frequency of the d allele be after one generation (assume that the reverse mutation d to D does not occur)?
0.400006
The sum of the frequencies of all the alleles of a particular gene in a population is always
1
Order the events that a population undergoing inbreeding depression might experience, starting at the top.
1. Population size is dramatically reduced by habitat destruction 2. The population experiences high level of inbreeding due to its small size 3. The mean fitness of the population decreases, which leads to a decrease in its reproductive success 4. The population size decreases even more, possibly leading to extinction
Typical mutation rate (with proper units) for a gene in a natural population
10^-6 per gene per generation
Horizontal gene transfer (HGT) between species of bacteria is relatively common. In fact, scientists estimate that as much as
20-30% of the genetic variation between modern bacteria can be attributed to HGT.
What is the probability of elimination due to genetic drift of a newly arising allele in a population of 100 individuals?
99.5%
Consider a population, for which you know the allele composition of three genes. Gene A has three alleles in the following proportions: A1- 34.4%, A2- 30%, A3- 35.6%. Gene B has two alleles in the following proportions: B1- 67.1%, B2- 32.9%. Gene C has two allels in the following proportions: C1- 99.2%, C2- 0.8%. Which of those genes is(are) polymorphic?
A and B only
Repetitive sequences are composed of a certain sequence that is repeated many times throughout the genome of a species. What is the typical size of the sequence that is being repeated?
A few to a few thousand base pairs
What is exon shuffling?
A novel gene that may encode a protein with a novel combination of functional domains
You are studying a rare disease, which affects 1 out of 10000 individuals. The disease is caused by a gene with two allels: D, and d. Individuals with dd genotype are affected, while individuals with a Dd phenotype are unaffected carriers. What is the expected frequency of unaffected carriers in the population, assuming this gene is in Hardy-Weinberg equilibrium?
Approx 2%
Why are repetitive sequences, such as micro and minisatellites an extremely useful tool for studying population genetics?
Because they tend to exhibit considerable variation between individuals
You are studying two areas inhabited by a species of frog. In area X, ponds inhabited by the frogs are less frequent and frogs rarely move from one pod to another. In area Z, ponds inhabited by these frogs are connected by a man made system of channels, which allows free movement of frogs between ponds. What will accurately describe the differences in allele frequencies between different ponds within each area?
Each pond in area X should have different allele frequencies, while the allele frequencies in all ponds in area Z are likely to be very similar.
Which of the following formulas allows us to calculate the expected number of mutations in a gene in a population
Expected number of new mutations= 2Nu
Over time, genetic drift can lead to the fixation of an allele. What types of alleles are usually fixed by drift?
Genetic drift is random, so deleterious, beneficial, or neutral alleles can become fixed.
What is a major disadvantage of inbreeding in natural populations?
Inbreeding lowers the mean fitness of a population when homozygotes have a lower relative fitness value
Which phenomena is responsible for introducing new genetic variation in a population?
Mutation
Consider a population of a hypothetical animal whose fur is determined by a single gene, called Col. What are all the conditions that must be met in order for this population to be in Hardy-Weinberg equilibrium for the Col gene
No natural selection. Animals in the population mate mate randomly, regardless of their genotype for the Col gene. No new mutations in the Col gene. The population must be large enough, so that no genetic drift is occuring
A change in one nucleotide in a gene is also known as a ____-nucleotide _____, or, SNP.
Single; polymorphism
Natural populations are dynamic entities. What features of populations can change from one generation to the next?
Size; genetic composition; geographic location
Which of the following describes a situtation, in which the predominant genotype in a population in Hardy-Weinberg equilibrium is the heterozygote? Assume that the gene of interst has only two alleles: G and g
The allele frequencies of both G and g are intermediate in value
Consider a population and a gene that has two alleles in this population, designated as P and p. If you divide the number of all copies of the p allele in the population by the total number of copies of both alleles (P and p) in the population, you will calculate
The allele frequency of the p allele
Which of the following is a similarity between microsatellites and minisatellites?
They consist of many tandem repeats of a certain DNA sequence
The human population known as the Old Order Amish of Lancaster County exhibits an unusually high frequency of the genetic disease Ellis-van Creveld syndrome. What explains that observation?
This population was founded by a very small group of people
A large, healthy, natural population typically exhibits
a high level of SNPs
For random mating to occur, individuals must choose their mates irrespective of their genotype/phenotype. When this condition is violated, non-random mating is occurring, also known as _____ mating.
assortative
Most mutations are
deleterious or neutral
In nature, large populations are often composed of several smaller local populations, called
demes
The term genetic ___ refers to random change in the frequencies of alleles in a population.
drift
A population that has experienced a bottleneck is highly susceptible to genetic drift
during the initial bottleneck and during the generations following the bottleneck when the population size is small
The Hardy- Weinberg equilibrium is used as a null hypothesis, i/e., if a population is in Hardy-Weinberg equilibrium, then
evolutionary change is not occurring in this population
By looking at many different proteins and the genes that encode them in a variety of eukaryotic organisms, scientists have determined that a protein domain tends to be encoded by one or a few (usually adjacent)
exons
In DNA ____, an individual is characterized based on the repetitive sequences in his or her genome.
fingerprinting
In order to derive the Hardy-Weinberg equation, two scientists assumed that
gametes are independently chosen at random from the population's gene pool
The ___ ___ of a population consists of all of the alleles of every gene in all of the individuals of that population.
gene pool
DNA fingerprinting can be used to determine the relationship between humans (for example paternity) because closely related individuals, such as a father and his chils
have more similar DNA fingerprints than do more distantly related individuals
The transfer of genetic material from one species to another (regardless of the exact mechanism) is called
horizontal gene transfer
Sometimes, both alleles of a gene in a particular individual are identical because they were actually descended from the same common ancestor. The probability of that occurring is called the ____ coefficient.
inbreeding
Based on a pedigree, we can determine all of the inbreeding paths for an individual of interest. The inbreeding paths can be used to calculate the
inbreeding coefficient
A deme is
one of several local populations that make up a large population
When scientists study populations, they typically observe high levels of variation in many of the traits that characterize a species. In genetics, variations in traits at the population level are known as
polymorphisms
In genetics, a ____ of a sexually reproducing species consists of a group of individuals of that species, which occupy the same region, and can successfully ___ with each other.
population; reproduce
Mutations occur when the DNA of an organism changes. Changes often happen in gene ____, but may also involve the structure and number of ____.
sequences; chromosomes
A healthy population can become highly susceptible to genetic drift size if its size is dramatically reduced due to natural phenomena, such as earthquakes, or droughts. This is known as
the bottleneck effect
Microevolution is best described as
the change in a population's gene pool from generation to generation
A group of individuals from a larger population can migrate to a new area and establish a colony, which will be highly susceptible to genetic drift. This is known as
the founder effect
If an individual has an inbreeding coefficient of 7%, it means that
the probability that a gene in this individual is homozygous due to inheritance from a common ancestor is 7%
One way in which exon shuffling can occur is by ____ elements, which can insert exons from one gene into the sequence of another gene.
transposable
Consider two populations of the same species and a gene that is found in two alleles in both populations (alleles D and d). What values need to be known in order to calculate the change in the frequency of the allele D if some individuals migrate from one of the populations into the other.
- Frequency of D in the recipient population - Frequency of D in the donor population - Number of individuals in the recipient population before migration occurred - Number of individuals that migrate from the donor to the recipient population
Consider a population and a gene that has two alleles in this population, designated as D and d. If you divide the number of individuals with the genotype DD by the total number of individuals in the population, you will calculate
The genotype frequency of the DD genotype
What is the effect of population size (N) (if any) on the probability of fixation of a new allele due to genetic drift?
The higher N is, the lower the chance that a new mutation will become fixed.
When two genetically related individuals mate, it is called ____. In contrast, mating between unrelated individuals is known as ____.
inbreeding; outbreeding
Is the size of population related to the average number of generations needed to achieve fixation of a newly appeared mutation, and how?
The larger the population, the more generations will be required, on average, to achieve fixation of a new allele
Consider a population of crickets that occupies two fields separated by a road and two ditches. Crickets inhabiting the two fields comprise two local populations, or demes. What is the likelihood that a cricket will reproduce within its own deme compared to the likelihood a crickets will reproduce with a cricket from the other deme?
The likelihood of reproducing within a deme is much higher than the likelihood of reproduction between demes.
