the micro evolution of population Flashcards
what did biologists of darwin’s accept and reject?
accepted the idea of evolution, but not the mechanism of natural selection
since mendel and darwin were contemporaries, what could’ve happened?
they lived at the same time but mendel’s work were unappreciated at the time, so if darwin had an understanding of inheritance that could explain how variations arise in a population and get passed onto offspring, then his ideas would have gained more acceptance
what was a turning point for evolutionary theory?
population genetics - emphasizes genetic variation within a population and the importance of quantitative traits like polygenic inheritance traits
modern synthesis
integrates Darwin, Mendel, and different field ideas
1) population evolve, not individuals
2) natural selection is the most important mechanism for evolution
3) gradualism explains how lots of small changes over long periods of time bring about big changes
what is a population?
localized group of individuals of the same species
species
population that can interbreed and produce fertile offspring
how often is genetic material exchanged in 2 isolated populations? does this happen?
rarely
populations are not usually isolated and do not have such sharp boundaries
the closer two populations are, what happens to relatedness?
the more closely related they are
gene pool
the total of all genes in a population
what does a gene pool consist of?
all alleles at all gene loci in all members of a population
what is a fixed gene pool?
when all members of a population are homozygous for the same allele, but usually there are 2+ alleles for a gene
what doeS the Hardy-Weinburg theorem state?
the frequencies of alleles and genotype in a population’s gene pool remain constant across generations unless acted upon agents other than sexual recombination
A GENE POOL THAT IS NOT EVOLVING IS AT H-W EQUILIBIRUM
what does the HW equilibrium provide?
a baseline for tracking genetic structure of population across generations
HW equilibrium equation
p^2+2pq+q^2=1
p^2
probability of getting an AA phenotype
q^2
probability of getting an aa phenotype
p
frequency of the dominant allele A
q
frequency of the recessive allele A
2pq
frequency of heterozygous/carriers
rules of HW equation
solve for q first
1-q=p
mircoeveloution
generation to generation change in a population’s frequencies of alleles or genotypes
what is the scale of change of gene pools?
microscopic–therefore why it is called microevolution
when is micro evolution occuring?
even if just one genetic locus is changing allele frequencies amongst the entire gene pool
5 conditions that H-W can remain true
1) large population size
2) no immigrations or emigrations
3) no mutations
4) random mating
5) no natural selection
what causes a population to microevolve?
5 things opposing HW equilibrium
small population
immigration
mutations
selected mating
natural selection
genetic drift
results due to small population size
smaller the sample size, greater the deviation from the expected results
2 situations that lead to genetic drift
population bottleneck and founder effect by a small number of individuals
population bottleneck
occurs due to disasters like tornadoes, hurricane, and earthquake which reduce the size of a population drastically, killing victims randomly
representation of alleles will be underrepresented, overrepresented or even eliminated reducing genetic variability in a population
where else can genetic drift happen? how so?
when just a few individuals colonize an isolated island, lake, or new habitat
the smaller the sample size, the less genetic makeup of the colonist swill represent the gene pool of the larger population they left
founder effect
genetic drift in a new colony
why does gene flow occur?
because most populations are not completely isolated
how do populations gain/lose alleles
due to im/emigration
what does im/emigration do?
reduced differences between populations and can eventually turn 2 separate populations into one with common genetic structure
what happens if a mutation occurs in gametes?
can cause immediate change in the gene pool of a population
in the long run, they are important to evolution as they bring about genetic variability that serves as raw material for natural selection
how does non-random mating occur?
individuals mate with close neighbors versus those far away, promoting inbreeding
what happens as a result of inbreeding?
the genotype frequencies in a population express more recessive phenotypes
assortive mating
a type of non random mating when individuals select partners that are like themselves phenotypically, which increases the number of gene loci in the population that are homozygous
what does natural selection provide?
differential success in reproduction
what do populations consist of?
varied individuals and some leave more offspring
how is natural selection different than the other 4 ways HW cannot be maintained?
only one that adapts a population to its environment so it is able to maintain favorable genotypes in a population
morphs
when 2 or more forms of a character are present in a population, and the contrasting forms are morphs
when is a population polymorphic?
if the 2 or more morphs are in high frequency and very noticeable in a population
example of polymorphism
many morphs/coloring patterns with cats
examples of polymorphism with the human population
physical (appearance) and biochemical (blood group) characters
to what does polymorphism apply?
to only discrete characters that are “either-or” and not to traits that vary along a continuum
what do most species exhibit?
geographical variation - differences in genetic structure between populations
how does geographical variation come about?
due in part to differences in environmental factors from one place to another like elevations
cline
type of geographical variation
graded change in some trait along a geographic axis
when are mutations beneficial?
in changing environments
two ways to generate genetic variation
mutations and sexual recombination
with sexual recombination, how do members of a population differ?
due to the shuffling of alleles during meiosis to produce a wide variety of gametes
how does the fact that organisms are diploids preserve variation?
maintains and sometimes preserves a huge pool of alleles
how does natural selection preserve variation?
balanced polymorphism - as in the case of heterozygous advantage
heterozygous advantage with sickle cell anemia
heterozygous for sickle cells anemia helps fight against malaria while not being severely affected by the disease
heterozygous advantage with crops like corn
when plants are highly inbreed homozygous loci increases and this can stunt corn growth and decrease the ability of the plant to fight disease
what happens with crossbreeding between 2 inbred varieties?
brings about more variety and produced hybrids
neutral variations
variations that have no impact on reproductive success
ex. human fingerprints have no advantage even tho they are all different
what is it impossible to do with neutral variations?
to prove that an allele brings no benefits at all to the organism and what may be neutral may not be in another environment
what is the critical contribution an individual makes to the gene pool of the next generation?
traits that best fit the environment, enable natural selection, and have reproductive success that can be measured by Darwinian fitness
does survival guarantee reproductive success?
no- sterile animals leave no offspring
what is survival a prerequisite for?
reproducing
correlation between life length and offspring number?
longer one lives, the higher the chances of leaving more offspring
what does an organism expose to the environment?
its phenotype not genotype
what does natural selection act on?
phenotypes adapting to a population to its environment by increasing favorable genotypes in the gene pool
what three ways can natural selection affect the frequency of a trait in the population?
1) stabilizing selection
2) directional selection
3) diversifying/disruptive selection
stabilizing selection
acts against extreme phenotypes and favors the more common intermediate variants
directional selection
most common during periods of environmental change or when members of a population migrate to a new habitat with different environmental conditions
diversifying/disruptive selection
occurs when environmental conditions are varied in a way that favors individuals on both extremes of a phenotypic range over the intermediate phenotype
what can disruptive selection result in?
balanced morphism such as birds with 2 different beak sizes
sexual dimorphism
males and females of many animals species have distinct secondary sex characteristics
how is sexual dimophism expressed?
difference in size with males larger than females
colorful plumage in male birds
manes on male lions
antler on male deers
which is the more showier sex?
males as they attract females or compete with other males
how can showier secondary sex characteristic lead to problems?
showy plumage can attract predators
what does sexual dimorphism do to reproductive success?
enhances it, which perpetuates the alleles generation to generation
