Biology, Genes within population

College level Biology Raven 13th edition, CH20

Genetic Variation and Evolution : Genetic variation refers to

differences in alleles of genes found within individuals in a population

Genetic Variation and Evolution : Evolution is how

an entity changes through time

Evolution : Charles Darwin described evolution as

"descent with modification"

Many Processes Lead to Evolutionary Change : Unlike his predecessors, Darwin proposed

natural selection as the mechanism of evolution

Many Processes Lead to Evolutionary Change : Natural selection can lead to change in

allele frequencies

Population Genetics : Population genetics is the study of

properties of genes in a population

Population Genetics : Evolution results in a change in

the genetic composition of a population

Population Genetics : Genetic variation is required for

evolution to occur

Genetic Variation : Human blood groups are an example of variation due to

genetic differences

Genetic Variation : SNPs are used to assess patterns in

over 300 species

Genetic Variation : African genomes have

the most genetic variation

Changes in Allele Frequency : Scientists originally thought selection should

eliminate variation

Changes in Allele Frequency : Blending inheritance was widely accepted, where offspring were expected to be

phenotypically intermediate relative to parents

Hardy-Weinberg Principle : The Hardy-Weinberg principle predicts

genotype frequencies

Hardy-Weinberg Principle : For Hardy-Weinberg equilibrium, the proportions of genotypes do not change if

no mutation takes place

Hardy-Weinberg Principle : For Hardy-Weinberg equilibrium, the proportions of genotypes do not change if

no genes are transferred to or from other sources

Hardy-Weinberg Principle : For Hardy-Weinberg equilibrium, the proportions of genotypes do not change if

mating is random

Hardy-Weinberg Principle : For Hardy-Weinberg equilibrium, the proportions of genotypes do not change if

the population size is very large

Hardy-Weinberg Principle : For Hardy-Weinberg equilibrium, the proportions of genotypes do not change if

no selection occurs

Hardy-Weinberg Principle : The Hardy-Weinberg equation is

p² + 2pq + q² = 1

Making Hardy-Weinberg Predictions : If all 5 assumptions for Hardy-Weinberg equilibrium are true, allele and genotype frequencies

do not change from one generation to the next

Making Hardy-Weinberg Predictions : The primary use of the Hardy-Weinberg equation is to determine whether

evolutionary processes are operating in a population

Five Agents of Evolutionary Change : Mutation is

the ultimate source of variation

Five Agents of Evolutionary Change : Gene flow is

a very potent agent of change

Five Agents of Evolutionary Change : Nonrandom mating does not alter allele frequency, but

reduces the proportion of heterozygotes

Five Agents of Evolutionary Change : Genetic drift is

statistical accidents

Five Agents of Evolutionary Change : Selection is the only agent that produces

adaptive evolutionary changes

Agents of Evolutionary Change : Mutation rates are generally

low

Agents of Evolutionary Change : Mutation makes evolution possible because it is

the ultimate source of genetic variation

Agents of Evolutionary Change : Gene flow is the movement of alleles

from one population to another

Agents of Evolutionary Change : Gene flow can occur through

drifting of gametes or immature stages

Nonrandom Mating : In assortative mating,

phenotypically similar individuals mate

Nonrandom Mating : Assortative mating increases the proportion of

homozygous individuals

Nonrandom Mating : In disassortative mating,

phenotypically different individuals mate

Nonrandom Mating : Disassortative mating produces

an excess of heterozygotes

Genetic Drift : The magnitude of genetic drift is

inversely related to population size

Genetic Drift : Genetic drift can lead to

the loss of alleles in isolated populations

Genetic Drift : Uncommon alleles are

more vulnerable to genetic drift

Founder Effect : The founder effect occurs when

one or a few individuals disperse and become the founders of a new, isolated population

Founder Effect : In the founder effect, some alleles are

lost, and others change in frequency

Bottleneck Effect : The bottleneck effect is a

drastic reduction in population size

Bottleneck Effect : The bottleneck effect results in

loss of genetic variability

Selection Favors Some Genotypes Over Others : In artificial selection,

a breeder selects desired characteristics

Selection Favors Some Genotypes Over Others : In natural selection,

environmental conditions determine which individuals produce the most offspring

Evolution by Natural Selection : For evolution by natural selection to occur,

variation must exist among individuals in a population

Evolution by Natural Selection : For evolution by natural selection to occur, variation among individuals must result in

differences in the number of offspring surviving

Evolution by Natural Selection : For evolution by natural selection to occur, variation must have

a genetic basis

Evolution by Natural Selection : Natural selection and evolution are not the same; natural selection is

a process

Evolution by Natural Selection : The result of evolution driven by natural selection is that populations become

better adapted to their environment

Selection to Avoid Predators : In pocket mice, populations living on rocks favor

dark color

Selection to Avoid Predators : In pocket mice, populations living on sand favor

light color

Selection to Match Climatic Conditions : Enzyme allele frequencies often vary with

latitude

Selection for Pesticide and Microbial Resistance : Widespread use of insecticides has led to the rapid evolution of

resistance in more than 500 pest species

Selection for Pesticide and Microbial Resistance : The evolution of resistance to

antibiotics is dangerous for human health

Quantifying Natural Selection : Fitness is a relative concept where the most fit phenotype is the one that produces

the greatest number of offspring

Measuring Fitness : The most fit phenotype is assigned a fitness value of

1

Many Components of Fitness : Components of fitness include

survival and sexual selection

Many Components of Fitness : Traits favored for one component of fitness may be

a disadvantage for others

Reproductive Strategies : Males and females usually differ in how they

attempt to maximize fitness

Reproductive Strategies : Peahens prefer to mate with peacocks that have

more eyespots on their tailfeathers

Parental Investment : Parental investment refers to

the energy and time each sex invests in producing and rearing offspring

Parental Investment : Females have a

higher parental investment

Parental Investment : Males best increase their fitness by

mating with as many females as possible

Parental Investment : Females are limited by

the number of eggs that can be produced

Sexual Selection : Intrasexual selection involves

competitive interactions between members of one sex

Sexual Selection : Intersexual selection involves

mate choice

Sexual Selection : Secondary sexual characteristics include

antlers and horns used to combat other males

Sexual Selection : Sexual dimorphism refers to

differences between sexes

Sexual Selection : Sperm competition selects for features that increase the probability that

a male’s sperm will fertilize the eggs

Intrasexual Selection : In intrasexual selection, a few successful males may engage in

an inordinate number of matings

Intersexual Selection : Direct benefits of mate choice include

the male providing the best care

Intersexual Selection : Indirect benefits of mate choice include

higher-quality offspring

Intersexual Selection : The handicap hypothesis suggests that

only genetically superior mates survive with a handicap

Sensory Exploitation : Sensory exploitation is the evolution in males of

a signal that exploits preexisting biases

Sensory Exploitation : In the tungara frog, females are particularly attracted to

a short burst of sound at the end of the male's call

Natural Selection's Role in Maintaining Variation : In frequency-dependent selection, the fitness of a phenotype depends on

its frequency within the population

Natural Selection's Role in Maintaining Variation : Negative frequency-dependent selection favors

rare phenotypes

Natural Selection's Role in Maintaining Variation : Positive frequency-dependent selection favors

the common form

Oscillating Selection : In oscillating selection, selection favors

one phenotype at one time and another phenotype at another time

Oscillating Selection : The effect of oscillating selection is to

maintain genetic variation in the population

Heterozygote Advantage : In heterozygote advantage,

heterozygotes are favored over homozygotes

Heterozygote Advantage : Heterozygote advantage works to maintain

both alleles in the population

Sickle Cell Allele : The sickle cell allele is not eliminated because heterozygotes are

much less susceptible to malaria

Selection Acting on Traits Affected by Multiple Genes : Many traits are affected by

more than one gene

Selection Acting on Traits Affected by Multiple Genes : The three types of selection are

disruptive, directional, and stabilizing

Disruptive Selection : Disruptive selection acts to

eliminate intermediate types

Directional Selection : Directional selection acts to

eliminate one extreme

Stabilizing Selection : Stabilizing selection acts to

eliminate both extremes

Experimental Studies of Natural Selection : To study evolution, biologists have traditionally investigated

what has happened in the past

Natural Selection in Guppies : Guppy males are larger and gaudier in environments where

predators are rare

Natural Selection in Guppies : Guppies in high-predation environments are

smaller and drab

Interactions Among Evolutionary Forces : Selection usually overwhelms genetic drift except in

small populations

Interactions Among Evolutionary Forces : Gene flow can be constructive by

spreading beneficial mutations to other populations

Interactions Among Evolutionary Forces : Gene flow can be constraining by

impeding adaptation through the flow of inferior alleles

Limits of Selection : A limit to selection occurs when

the same gene affects multiple traits

Limits of Selection : Another limit to selection is

lack of genetic variation

Limits of Selection : Phenotypic variation may not have a genetic basis due to

interactions between genes