Chapter 27: Population Genetics

population genetics

the field of genetics that is primarily concerned with the extent of genetic variation within a group of individuals and changes in that variation over time

gene pool

all of the alleles of every gene within a particular population

population

a group of individuals of the same species that occupy the same region and can interbreed with one another

local population

a segment of a population that is somewhat isolated. Members of a local population are more likely to breed with each other than with members of a more distant population.

local populations, breed, geographic

* A large population usually is composed of smaller groups called _____ _____.
* members are far more likely to _____ among themselves than with members of the same species from a more distant population
* often separated from each other by moderate _____ barriers

size, geographic location, genetic composition

a population may change its:


1. _____
2. _____ _____
3. _____ _____

polymorphism

* variation in traits that are observable with the naked eye
* the prevalence of two or more phenotypic forms in a population
* the phenomenon in which a gene exists in two or more alleles within a population

polymorphic

a term used to describe a trait or gene (or other segment of DNA) that is found in two or more forms in a population

monomorphic

a term used to describe a trait that is found in only one form in a population or a gene that is found as only one allele in a population

single-nucleotide polymorphism (SNP)

a genetic polymorphism within a population in which two alleles of the gene differ by a single nucleotide

allele frequency

the number of copies of a particular allele in a population divided by the total number of all alleles for that gene in the population

genotype frequency

the number of individuals with a particular genotype in a population divided by the total number of individuals in the population

monomorphic

if a gene is _____, the allele frequency for the single allele will be equal to or slightly less than a value of 1.0

polymorphic

for _____ genes, the allele frequencies for all of the alleles in the population will be 1.0

Hardy-Weinberg equilibrium

the phenomenon by which, under certain conditions, allele frequencies are maintained in a stable condition and genotypes can be predicted

null, not

the Hardy-Weinberg equilibrium is a _____ hypothesis, which suggests that evolutionary change is _____ occurring (unchanging allele and genotype frequencies from generation to generation)

no new mutations, no genetic drift, no migration, no natural selection, random mating

certain conditions of Hardy-Werinberg

no, large

* in reality, _____ population satisfies Hardy-Weinberg equilibrium completely


* in _____ natural populations with little migration and negligible natural selection, Hardy-Weinberg equilibrium may be nearly approximated for certain genes

microevolution

changes in a population’s gene pool with regard to particular alleles over measurable periods of time

mutation, random genetic drift, migration or gene flow, natural selection, nonrandom mating

factors that govern microevolution (change allele frequencies)

random, mutagens, evolution, evolution, alleles, survival, reproductive, beneficial, neutral, deleterious

mutation

* _____ events that occur spontaneously at low rates
* rates are increased by _____
* raw material for _____ but does not constitute _____ itself
* produces new _____, but does not act as a major force dictating the final balance
* look at new mutations as they affect the _____ and _____ potential of the individuals that inherits them
* new mutations may be:
* _____
* _____
* _____

genetic drift

changes in allele frequencies in a population due to random fluctuations

random, loss, fixation, monomorphic, more, rare

genetic drift

* changes in allele frequencies in a population due to _____ fluctuations
* favors either the _____ or _____ of an allele over many generations
* fixed allele is _____ - cannot fluctuate
* rate depends on population size:
* large: new mutations are _____ common however it will most likely be eliminated
* small: new mutations are _____ but has a greater chance of being fixed

bottleneck effect, founder effect

types of genetic drift

bottleneck effect

a mechanism that can give rise to genetic drift; occurs when most members of a population are eliminated without any regard to their genetic composition

natural disaster, randomly, less, African cheetah

bottleneck effect

* populated is reduced dramatically
* caused by _____ _____ (earthquakes, floods, droughts, or human destruction of habitat)
* _____ eliminate most of the members of the population without regard to their genetic composition
* the new population has _____ genetic variation than the original large population
* large, genetically diverse population → bottleneck: fewer individuals, less diversity → large, less genetically diverse population
* example: _____ _____
* substantial amount of genetic variation lost by bottleneck effect
* decreased genetic variation

founder effect

a change in allele frequency that occurs when a small group of individuals separates from a larger population and establishes a colony in a new location

less, differ, Old Order Amish

founder effect

* a small group of individuals separates from a larger population and establishes a colony in a new location
* the founding population has _____ genetic variation than the original population from which it was derived
* the allele frequencies in the founding population may _____ from those of the original population
* example: _____ (3 words)

gene flow

transfer of alleles or genes from one population (a donor population) to another, thereby changing the recipient population’s gene pool

unidirectional, bidirectional, enhances, reduces

gene flow (migration)

* migration of fertile individuals from one population to another population and the successful breeding of such migrants with the members of the recipient population
* _____: migration between populations occurring in one direction
* _____: migration between populations occurring in both directions


* _____ genetic diversity within a population
* _____ differences in allele frequencies between neighboring populations

conglomerate population

a population composed of members of an original population plus new members that have migrated from another population

natural selection

refers to the process whereby differential fitness acts on the gene pool. When a mutation creates a new allele that is beneficial, the allele may become prevalent within future generations because the individuals possessing the allele are more likely to reproduce and pass it to their offspring.

vary, more, differential survival, mating efficiency, fertility

natural selection

* phenotypes _____ with regard to reproductive success
* individuals with higher reproductive success are _____ likely to produce offspring, and thereby pass certain alleles to the next generation
* related to:
* _____ _____
* _____ _____
* _____

Darwinian fitness

the relative likelihood that a genotype will contribute to the gene pool of the next generation compared to other genotypes

directional, stabilizing, disruptive, balancing

four patterns of natural selection

directional selection

favors individuals at one extreme of a phenotypic distribution that are more likely to survive and reproduce in a particular environment

stabilizing selection

the extreme phenotypes for a trait are selected against, and those individuals with intermediate phenotypes have the highest fitness values

stabilizing

laying eggs is an example of _____ selection

* too many drains resources to care for young
* too few does not contribute enough to population

disruptive selection

favors the survival of two or more different phenotypes

diverse, speciation

disruptive selection

* the fitness values of particular genotypes are higher in one environment and lower in a different one
* likely to occur in populations that occupy _____ environments
* some members of the species are more likely to survive and reproduce in each type of environmental conditions
* leads to _____

balancing selection

a pattern of natural selection that favors the maintenance of two or more alleles in a population; it may be due to heterozygote advantage or negative frequency-dependent selection

heterozygote advantage

a heterozygote has greater reproductive success than either of the corresponding homozygotes

fixation, elimination, heterozygote

balancing selection

* a polymorphism reaches an equilibrium where opposing forces balance each other (both dominant and recessive provide benefits)
* not evolving toward allele _____ or _____
* _____ is at a selective advantage

negative frequency-dependent selection

a pattern of natural selection in which the fitness of a genotype decreases when its frequency becomes higher

higher, rare, common, rare, common

negative frequency-dependent selection

* the fitness of a genotype decreases when its frequency becomes _____
* _____ individuals have a higher fitness than more _____ individuals
* _____ individuals are more likely to reproduce
* _____ individuals are less likely to reproduce
* produces balanced polymorphism in which no genotype becomes too rare or too common

rewardless, common, rare, increases

example of balancing selection: _____ flower (no nectar)

* pollinators learn to avoid _____ flower color with no nectar
* they visit the _____ flower more frequently (nectar)
* the relative fitness of the less-common flower _____

random mating

individuals reproduce with each other irrespective of their genotypes and phenotypes. This condition is violated frequently.

assortative mating

sexual reproduction in which individuals preferentially breed with each other based on their phenotypes (nonrandom mating)

positive assortative mating

mating occurs when individuals with similar phenotypes (similar traits) reproduce with each other

negative assortative mating

mating occurs when individuals with dissimilar phenotypes (opposite traits) reproduce with each other

inbreeding

sexual reproduction between two genetically related individuals

outbreeding

sexual reproduction between genetically unrelated individuals

smaller, homozygotes, heterozygotes, higher, recessive, inbreeding depression

inbreeding

* gene pool is _____ because parents are genetically related
* no change in allele frequencies
* increases proportion of _____ and decreases that of _____
* positives:
* agriculture
* _____ proportion of homozygotes, which may exhibit a desirable trait
* makes plant inviable (energy is used for fruit/flower)
* negatives:
* many genetic diseases are inherited in a _____ manner (inbreeding increases the likelihood that an individual will be homozygous for the recessive allele and therefore afflicted with the disease)
* _____ _____: the phenomenon in which inbreeding produces homozygotes that are less fit, thereby decreasing the reproductive success of a population

sexual reproduction (eukaryotes), gene transfer (prokaryotes), DNA point mutations, changes in chromosome number or structure, exon shuffling, horizontal gene transfer, repeated sequences

sources of genetic variation

exon shuffling

the phenomenon in which an exon and its flanking introns from one gene are inserted into another gene

modular, functions, exon, introns, domain, transposable elements

exon shuffling

* proteins are commonly _____
* discrete domains with specific _____


* an _____ and flanking _____ from one gene are inserted into another gene, thereby producing a new gene that encodes a protein with an additional _____
* _____ _____ may promote the insertion of exons into the coding sequences of genes

horizontal gene transfer

the transfer of genes from one individual to another individual that is not its offspring

another, offspring, different

horizontal gene transfer

* an organism incorporates genetic material from _____ organism without being the _____ of that organism
* commonly between _____ species

repetitive sequences

short DNA sequences that occur many times within a species’ genome

transposable elements, microsatellites, proofreading, hotspots

repetitive sequences

* two types
* _____ _____: DNA sequences that can move from place to place in a species’ genome
* _____: DNA sequences that are nonmobile and consists of short sequences that are tandemly repeated (AAC)
* commonly escape _____ by polymerases
* mutation “_____”

DNA fingerprinting

a technology for identifying a particular individual based on the properties of his or her DNA

repetitive, unique

DNA fingerprinting

* analyzes individuals based on the occurrence of _____ sequences in their genome
* each individual will have a _____ pattern