Exam 3: Population and Evolutionary Genetics I Flashcards
define population genetics
study of the distribution and change in frequency of alleles within populations
evolution is a change in _
gene frequency over time in a population which leads to speciation and divergence
what can change gene frequency
environmental stress/pressures can modify gene expression patterns and genetic make-up
reproductive success is measured by
of offspring left behind and quality/probable fitness
there is a lot of variation in living organisms. why is that important for species survival
if a organism can adapt, then those minor differences/variation mean the organism has the ability to respond to changing environments to survive and reproduce
what is it about the bighorn sheep in 1922
population was disappearing as there was not enough variation because hunter were killing off males (genetic drift/founder effect). Repaired variety in population by introducing a new bighorn sheep from other populations
define population
group of interbreeding, sexually reproducing individuals sharing a common set of genes
define genetic variation
gene frequencies are affected by evolutionary forces: mutation, gene flow, genetic drift, and nonrandom mating, natural selection
example of gene flow
human beings bringing in new sheep = new individuals and new genetic material
example of genetic drift
genes disappearing from population/cause of change in gene frequency by random events. usu in small populations
nonrandom mating
selective selection (behavioral)
natural selection
environmental influences that allow certain individuals to prosper and leave behind those advantageous genes
what is the history of the hardy-weinberg law
theory to help understand process of natural selection and evolution
calculating genotypic frequencies mean:
(# of individuals possessing the genotype)/(total # of individuals in sample)
calculating allelic frequencies means:
(# of copies of a particular allele present in a sample)/(total # of alleles)
loci with multiple alleles and x-linked loci are calculated
similarly
definition of hardy-weinberg law
allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences
hardy-weinberg law: assumptions
population is large, randomly mating, not affected by mutation, migration, or natural selection (rare no change in gene frequency)
hardy-weinberg law: prediction 1
the allelic frequencies of a population do not change
hardy-weinberg law: prediction 2
the allelic frequencies stabilize
p^2
homozygous dominant allele pair frequency (1/4 cross btwn 2 hets)
q^2
homozygous recessive allele pair frequency (1/4 cross btwn 2 hets)
2pq
heterozygous allele frequency (1/2 cross btwn 2 hets or 2 out of 4)
p + q = 1 when
there are only 2 alleles in a population
genotype frequencies may be predicted for the next generation if hardy-weinberg assumptions hold true. Does this ever happen?
no; very rare. selective pressures are acting all the time on organisms causing them to evolve to adapt and survive
frequencies of alleles can be calculated from #s of
genotypes
the sum of all the genotypic of allelic frequencies in a sample always =
1
when a population is in hardy-weinberg equilibrium, the proportions of genotypes are determined by
the frequencies of the alleles
when the frequency of one allele is high, most of the individuals are
homozygotes
the frequency of the heterozygote is greatest when
allelic frequencies are equal (p=q=0.5)
positive assortative mating
a tendency of like individuals to mate
negative assortative mating
a tendency of unlike individuals to mate
what other sorts of nonrandom mating occur
nonrandom mating/inbreeding two types:
- assortative mating (mating between individuals with similar phenotypes or among individuals that occur in a particular location) or
- inbreeding (mating between related individuals)
nonrandom mating may have similar consequences since
Both types of nonrandom mating may have similar consequences since individuals with
similar phenotypes often have similar genotypes.
individuals with similar phenotypes may mate because
a) phenotypic assortative mating occurs;
b) mating with relatives is preferred;
c) matings are primarily based on proximity
inbreeding is a measure of
the probability that two alleles are identical by descent alleles descended from the same copy in a common ancestor ex Hemophilia in the Royal Families of Europe
by “descent”
2 individuals come together w/ common ancestor, likely to share a gene from that ancestor and pass it on
alleles identical by state
alleles that are the same in structure and function but are descended from two different copies in ancestors (nonrelated; 2 diff copies in ancestors)
inbreeding depression
- incr appearance of lethal and deleterious traits with inbreeding
- inbreeding incr the % of homozygous individuals in the population
- need to bring in variation*
outcrossing
is the avoidance of mating btwn related individuals
which of the basic assumptions are violated when inbreeding occurs
- mating w/ themselves
- variation is lost
- inbreeding leads to homozygosity at almost all alleles
as inbreeding increases, the avg yield of corn decreases, why?
no genetic variation = poor yield (genetic variation amongst all alleles lose robustness as become more universally homozygous)
under what conditions can inbreeding be advantageous
- inbreeding can uncover (recessive) deleterious alleles; this can lead to the elimination (death of homozygotes) of these alleles in the population
- can keep together good combinations of genes that might be broken up by outcrossing
what conditions might favor inbreeding
environment and individuals w/in it are stable; has a perfect set of genes that you do not want variation
Two alleles are “identical by descent” if
(1) both are descended from the same allele in a common ancestor
or
(2) one allele is descended from the other
The inbreeding coefficient of an individual
is the probability that its two gene copies at a locus are identical by descent
