Exercise 1 Flashcards
What evolve?
populations
what four things cause evolution?
1) natural selection
2) genetic drift
3) gene flow
4) mutation
what is the HW principle?
gives mathematical proof that allele frequencies do not change from generation to generation in diploid, sexually reproducing populations simply as a result of sexual reproduction and recombination
what 5 conditions must be true in order for a population to be in HW equilibrium?
1) large population size
2) no gene flow (immigration/emigration)
3) no net mutations
4) random mating
5) no natural selection
what is natural selection?
the process in which organisms with certain inherited characteristics are more likely to survive and reproduce than organisms with other characteristics
what happens if a population is in HW equilibrium?
no change in allelic frequencies
what’s the point of HW if the conditions are basically never met?
it represents a null model against which we can test observations to see whether evolution is occurring
if there are 600 roaches, how many alleles are in the population?
1200
each individual has two alleles
in a population of 600 roaches, 900 are A. what is the allelic frequency of A? a?
F(A) = 900/1200 = .75 –> p
F(a) = 300/1200 = .25 –> q
p + q = 1
what is F(A) or F(a)?
The allelic frequency
how do you find the genotypic frequencies?
p^2 + 2pq + q^2 = 1
what does p^2 represent?
the likelihood of receiving A from both parents
the expected frequency of the AA genotype among offspring
what does q^2 represent?
the likelihood of receiving the aa genotype
what does 2pq represent?
the likelihood of receiving the Aa genotype
what did HW show?
sexual reproduction has no effect by itself on allele frequencies
F(A) = p in the next generation –> the proportion of A is the same as the parental population
F(a) = q also
how do you find the number of homozygous dominant individuals if you know that p=.75?
so you know that the genotypic frequency of AA is p^2 =(.75)^2 = 0.5625
to find the actual # of homozygous dominant individuals you multiple the frequency by the population size to get (.5625)(600) = 336
what is genetic drift?
through random chance, gene frequencies change from generation to generation even when all HW assumption (except infinite population size) are satisfied
most noticeable in small populations
what are two types of genetic drift that occur when a population is greatly reduced but then recovers to a greater size?
1) founder effect
2) population bottleneck
what is the founder effect?
when a few individuals from an original population disperse and inhabit a new area
the genetics of these few individuals will be passed on to all the offspring in the newly inhabited area and therefore the genetic diversity of this population will be less comprehensive compared the the original population
what is a population bottleneck?
occurs when a population is greatly reduced but then recovers
because relatively few individuals survive the bottleneck they pass on their less diverse genetic diversity on to the rest of the growing population
ex. cheetahs
what is essential for evolution?
variation
what is phenotypic plasticity?
where physical traits vary among individuals based on individual pressures, not on genotype
ex. the lizards that are white and hatched on sand beaches are moved to black lava beds develop dark coloration
in the experiment, why were the frequencies obtained in the first generation might have deviated somewhat from the original .5 values?
the cause of the deviation is due to the small gene pool which causes greater deviation in the frequency of the alleles
would the deviation from the original frequencies be larger or smaller if more than 25 individuals were drawn per generation for an infinite number of generations?
the deviation would be smaller because of the bigger population
like the odds when flipping a coin
why do zoologists encourage sharing threatened and endangered animals among different zoos as breeding partners rather than breeding only the animals within their own zoo?
they want to increase genetic variation and make sure than not only a certain set of alleles will become common and decrease variation
decreased variation could eventually cause evolution of the species to stop
interbreeding would prevent this from happening because new alleles are being presented into population through genetic drift –> not sharing animals decreases the effect of genetic drift
Why do blood types vary between locations and/or cultures?
the centralized location of certain blood types is the result of population isolation and lack of genetic drift for many generations
the lack of allele variation causes the percent of the population of a certain to have high frequency of on particular blood type
what is a fixed allele?
genetic drift sometimes causes an allele to become fixed, meaning it is the only allele left in the population
if an allele is fixed what influence can natural selection can have on its frequency?
if an allele is fixed, it’s the only allele in the gene pool and natural can’t occur
no variation = no evolution
