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Chapter 26

Terms in this set (54)

Population genetics
the field of genetics that is primarily concerned with the prevalence of genetic variation within populations
Gene pool
The collection of alleles that exists in a population.
Genetic variation
Term used to describe differences between individuals with respect to their DNA.
Population
a group of individuals of the same species that occupy the same region and can interbreed with one another
Polymorphism
The observation that many traits display variation in a population.
Polymorphic
Term used to describe a gene that commonly exists as two or more alleles in a population
SNP
single-nucleotide polymorphism; Smallest type of genetic changes that can occur within a gene and are also the most common; represents 90% of all the variation in DNA sequences that are present in humans.
Polymorphisms are ____ in natural populations.
common
Allele frequencies
the number of copies of a particular allele in a population divided by the total number of all alleles for that gene in a population
Genotype frequencies
the number of individuals with a particular genotype in a population divided by the total number of individuals in the population
Hardy-Weinberg equilibrium
the phenomenon by which, under certain conditions, allele frequencies are maintained in a stable condition and genotypes can be predicted according to the Hardy-Weinberg equation
Hardy-Weinberg equation
p2 + 2pq + q2 = 1
Mutation
A permanent change in the base sequence of DNA; a source of new allelic variation, random mutations within preexisting genes introduce new alleles into populations, but at a very low rate
Genetic drift
The chance alteration of allele frequencies in a small population, with a significant effect on the population's genetic structure
Migration (immigration or emigration)
Movement of organisms from one location to a distant location; Two forms: Immigration (to enter the population) and Emigration (to leave the population).
conditions that need to be met in a population with regard to the gene of interest that predicts equilibrium
No new mutations, no genetic drift, no migration, no natural selection, and random mating
Natural selection
Form of selection. Organisms that are more successful in a particular environment will pass on their alleles to the next generation in greater relative frequency.
Random mating
the members of a population mate with each other without regard to their phenotypes and genotypes
nonrandom mating
Term used to describe the situation that each individual in a population doesn't have an equal opportunity to mate with any other individual (of the opposite sex) in the population.
Microevolution
Term that describes changes in a population's gene pool from generation to generation.
allelic variation
genetic variation in a population that involves the occurrence of two or more different alleles for a particular gene
genetic variation
variations of genomes between members of species, or between groups of species thriving in different parts of the world as a result of genetic mutation.
Darwinian fitness
the relative likelihood that one genotype will contribute to the gene pool of the next generation compared to other genotypes
Directional selection
A mode of selection in which one of the pheneotypic extremes has a higher fitness in that particular environment. Therefore, over generations the frequency of this phenotypic extreme will become more frequent.
Balancing selection
A pattern of natural selection that favors two or more alleles in a more homogeneous environment; results in genetic polymorphism in a population.
Heterozygote advantage
The heterozygote has a higher fitness than either of the corresponding homozygotes.
selection coefficient
measures the degree to which a genotype is selected against (s=1-w), genotypes with the highest fitness have an s value of 0
disruptive selection
A mode of selection in which intermediate phenotypes of a particular trait are selected against so that over generations, the frequency of the extreme phenotypes will increase.
negative frequency-dependent selection
the rarer phenotype has a higher fitness which increases its reproductive success
does disruptive selection favor polymorphism?
Yes because the fitness levels depend on the environment. Some phenotypes are fittest in certain environments.
stabilizing selection
the extreme phenotypes for a trait are selected against and those individuals with intermediate phenotypes have the highest fitness values
How does population size affect genetic drift?
It tends to have a greater affect on smaller populations. It can lead to rapid loss or fixation of an allele.
Bottleneck effect
A change in a population's allele frequencies (due to chance) that follows a sharp reduction in the size of the population; May cause genetic drift.
Founder effect
A situation in which the initial gene pool for a population is established by means of that population migrating to a new area; May cause genetic drift.
Gene flow
refers to the transfer of alleles or genes from one population (a donor population), thereby changing the gene pool of a recipient population
Unidirectional migration
Migration of a species in one direction only without changing direction
bidirectional migration
Migration of a species in two separate directions.
Assortative mating
when mating is nonrandom in a population
Positive assortative mating
occurs when individuals with similar phenotypes choose each other as mates
negative assortative mating
occurs when individuals with dissimilar phenotypes mate preferentially
Inbreeding
mating of two genetically related individuals
Outbreeding
mating between unrelated individuals
Hybrids
offspring resulting from outbreeding that are heterozygous for many genes
Inbreeding coefficient (F)
the probability that two alleles in a particular individual will be identical for a given gene because both copies are due to descent from a common ancestor. Can be computed by analyzing the degree of relatedness from a pedigree
Independent assortment
The independent segregation of different homologous chromosomes may give rise to new combinations of alleles in offspring
crossing over
recombination between homologous chromosomes; can also produce new combinations of alleles that are located on the same chromosome
prokaryotic gene transfer
mechanisms of genetic transfer within prokaryotic species such as conjugation, transduction, and transformation
new alleles
point mutations within a gene can occur to create single-nucleotide polymorphisms (SNPs). In addition, genes can be altered by small deletions and additions
gene duplications
events, such as misaligned crossovers that can add additional copies of a gene into a genome and lead to the formation of gene families
chromosome structure and number
chromosome structure may be changed by deletions, duplications, inversions, and translocations; changes in the chromosome number result in aneuploid, polyploid, and alloploid offspring
exon shuffling
new genes can be created when exons of preexisting genes are rearranged to make a gene that encodes a protein with a new combination of protein domains
STR
short tandem repeats; a type of repetitive sequence that is nonmobile and involves short sequences that are tandemly repeated, usually 1-6 bp long and the whole repeat is less than a couple hundred base pairs in length
What is a gene pool? How is a gene pool described in a quantitative way?
A gene pool is all the genes present in a particular population and can be expressed through allele frequency.
What is a genetic polymorphism? What is the source of genetic variation?
Genetic polymorphism is the phenomenon in which a gene is found in two or more alleles within the population. Mutation is the ultimate source of genetic variation.
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