Test 2 Flashcards
Population genetics
Study of the distribution of alleles in populations and causes of allele frequency changes
Allele frequency
- The proportion of all copies of a gene that is made up of a particular gene variant (allele)
- the number of copies of a particular allele divided by the number of copies of all alleles at the locus in a population
In population genetics, allele frequencies are used to depict..
The amount of genetic diversity at the individual, population, and species level
Who developed an equation for population genetics?
Hardy and Weinburg
Hardy-Weinburg equilibrium
Population allele frequencies do not change if:
- population is infinitely large
- geneotypes do not differ in fitness
- there is no mutation
- mating is random
- there is no migration
Through mathematical modeling based on probability, they concluded that..
Gene pool frequencies are inherently stable but that evolution should be expected in all populations virtually all of the time
Hardy-Weinburg theorem proves that allele frequencies do not change in the absence of..
Drift, selection, mutation, and migration
Mechanisms of ___ are forces that change allele frequencies
Evolution
___ frequencies predict ___ frequencies
Allele, genotype
Predictions from Hardy-Weinburg
p^2 + 2pq + q^2
p - frequency of dominant allele
q - frequency of recessive allele
1 in 1700 U.S. Caucasian newborns have ___
Cystic fibrosis
Genetic drift
- along with natural selection, mutation, and migration - is one of the basic mechanisms of evolution
- simply the evolutionary equivalent of a sampling error
Hardy-Weinburg serves as the fundamental ___ in population genetics
Null model
Drift reduces ___ in a population
Genetic variation
Alleles are lost at a faster rate in ___ populations
Small
Bottlenecks ___ genetic variation
Reduce
A bottleneck ___ genetic drift
Causes
Population bottlenecks occur when..
A populations size is reduced for at least one generation
Founder effect
Occurs when a new colony is started by a few members of the original population
Both drift and founder effect result from __
Random sampling
Fitness
Reproductive success of an individual with a particular phenotype
Components of fitness
- survival to reproductive age
- mating success
- fecundity
Relative fitness
Fitness of a genotype standardized by comparison to other genotypes
Natural selection is more powerful in ___ populations
Large
___ weaker in large populations
Drift
Alleles that lower fitness experience ___ selection
Negative
Alleles that increase fitness experience ___ selection
Positive
Additive
Allele yields twice the phenotypic effect when two copies present
Dominance
Dominant allele masks presence of recessive in heterozygote
Estimate of new mutations each generation in humans
9.8 billion
Frequency-dependent selection
An evolutionary process where the fitness of a phenotype is dependent on its frequency relative to other phenotypes in a given population
In positive (diversifying) frequency-dependent selection,
The fitness of a phenotype increases as it becomes more common
In negative (purifying) frequency-dependent selection,
The fitness of a phenotype increases as it becomes rarer
Inbreeding coefficient
Probability that two alleles are identical by descent
Polygenic trait
Influenced by many genetic loci
- interaction between alleles (epistasis)
- interaction with environment (phenotypic plasticity)
Quantitative genetics
Study of the genetic mechanisms of continuous phenotypic traits
Epistasis
Phenomenon in which the expression of one gene depends on the presence of one or more “modifier genes”
A gene whose phenotype is expressed is called ___.
Epistatic
A gene whose phenotype is altered or suppressed is called ___.
Hypostatic
Phenotypic plasticity
Ability of an organism to change its phenotype in response to changes in the environment
Phenomenon in Daphnia, known today as cyclomorphosis
When exposed to the presence of a predator they respond by altering the shape of their body to produce a “helmet”
Heritability
Proportion of phenotypic variance due to genetic differences
Broad sense of heritability includes:
- additive effects
- dominance effects
- epistatic effects
- maternal/paternal environmental effects
Natural selection
Only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated
Natural selection will operate on anything that has the following properties:
- reproduction
- inheritance
- variation in fitness
- variation in individual characteristics
Directional selection
Favors those individuals who have extreme variations in traits within a population
- greyhound dog bred to run faster
Stabilizing selection
Favors the norm, the common, average traits in a population
- husky needs to be perfectly medium - too big will sink in snow, too small would not be strong enough
Disruptive selection
Favors extremes as well
Sudden changes in the environment creates a sudden force favoring that extreme
- changes in the environment when a meteor crashed into earth
How much the population changes depends on:
- Selection differential (S)
- Heritability
Selection coefficient
- Measure of the relative fitness of a phenotype
- s = 0 then is selectively neutral compared to the favored phenotypes
- s = 1 indicated complete lethality
Selection can occur without ___
Evolution
Quantitative trait loci (QTLs)
Stretches of DNA containing or linked to the genes that underlie a quantitative trait
Mapping regions of the genome that contain genes involved in specifying a quantitative trait is done using what?
Molecular tags, commonly SNPs
Quantitative traits
Phenotypes that vary in degree and can be attributed to polygenic effects
- color of coat in mice
Rapid change can lead to mismatch between ___ and ___.
Plastic traits and environment
The biological sciences now generally define ___ as being the sum total of the genetically inherited changes in the individuals who are the members of a populations gene pool.
Evolution
Diversity in darwins finches
Beak size
Variation in beak size influences what?
Efficiency at eating different types of seeds
Drought resulted in more __, __ seeds and favored _ beaked birds.
Hard, woody, larger
Light coat color evolved ___ in different populations
Independently
Evolution in response to natural selection is inevitable if:
- there is variation in a trait
- variation is heritable
- some variants reproduce more than others
___ can bring alleles to new locations
Gene flow
Aposematism favored only in areas where ___ co-occur
Coral snakes
Natural selection can lead variation over the ___ range of a species
Geographic
___ selection occurs when agents of selection act in opposing directions
Stabilizing
Gall flies
Stabilizing selection on gall size
Ability to digest lactose correlated with what?
Domestication of cattle
Domestic dog diversity created in last ___ years
15,000
Pesticides and herbicides act as agents of ___
Selection
Creation of refuges can slow the evolution of ___
Resistance
Introduced cane toads have led to evolution of ___ populations.
Black snake
Evolution of shorter male horns due to ___.
Hunting
The speed of evolution depends on amount of ___ and ___.
Amount of genetic variation and strength of selection
Sex creates new ___
Genotypes
Disadvantages of sexual reproduction
- twofold cost of sex
- search cost
- reduced relatedness
- risk of stds
Advantages of sexual reproduction
- combining beneficial mutations
- generation of novel genotypes
- faster evolution
- clearance of deleterious mutations
In the contest to explain sex, only ___ hypotheses remained in contention
Two
The deleterious mutation hypothesis
Sex exists to purge a species of damaging genetic mutations
- Kondrashov
In an asexual population, every time a creature sides because of a mutation,
The mutation dies with it
If the ones with lots of mutations die, then
Sex purges the species of mutations
Why eliminate mutations this way, rather than correcting more of them by better proofreading?
It may be cheaper to allow some mistakes through and remove them later
The rate of deleterious mutations must exceed ___ per individual per generation is sex is to earn its keep eliminating them
One
Red queen hypothesis
- Valen
- it takes all the running you can do, to keep in the same place
- hosts and disease, predator and prey
- sex is needed to fight disease
- advantages of sex and constant coevolutionary arms races
Heterozygosity and polymorphism are lost when…
A lineage becomes inbred
Hamilton built a..
Computer model of sex and disease
Some species can reproduce both sexually and asexually
Strawberry plants
Sponges
Water fleas
Sex creates new genetic variation by..
Mixing parental alleles
Ecological situations that require rapid evolution are likely to favor __
Sex
Asexual lineages have evolved mechanisms that compensate for ..
Lack of sex
___ results in differential investment in reproduction
Anisogamy
Anisogamy
Form of sexual reproduction involving the union or fusion of two dissimilar gametes
Limitations of reproductive success differ for the sexes
Females are limited by fecundity
Males are limited by the number of mates they can obtain
Investment differences can extend past ___
Fertilization
Uncertain paternity may explain why..
Male parental care is rare
Asymmetrical parental care alters what?
Operational sex ratio
Operational sex ratio
Ratio of males to females capable of reproducing at a given time
Ornaments
Attractive traits that increase mating success
Armaments
Weaponry used to outcompete other individuals
Selection is a two-way street
Male competition
female choice
Benefits of female choice
- direct benefits
- indirect benefits
Direct benefits
Benefit the female directly
Food, nest sites, protection
Indirect benefits
Benefits that affect the genetic quality of the females offspring
Males may compete for __
Territory
Competing for mates is __
Costly
Females may benefit from ___
Cannibalism
Voluntary ___ in redback spiders
Self-sacrifice
Female preferences are often ___
Consistent
Female preferences may arise from..
Preexisting sensory bias
Monogamy
One male pairs with one female
Sexual monogamy
Partners mate with each other exclusively
Social monogamy
Partner pair but may cheat
Polygyny
Males mate with multiple females
Polyandry
Females mate with multiple males
Development of weapons can involve what?
Trade-offs
Ornaments can serve as what?
Handicaps
___ selects for male traits that increase paternity
Polyandry
Sperm competition drives evolution for what?
Larger testes
Sexual conflict results in what?
Antagonistic coevolution
Sexual conflict
Traits that confer a fitness benefit on one sex but cost to the other
