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Biology Ch. 12 - Genetics and Evolution
MCAT
38
Biology
Undergraduate 1
05/28/2016

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Term
hemizygous
Definition
having only one allele
Term
complete dominance
Definition
when only one dominant and one recessive allele exist for a given gene
Term
codominance
Definition
when more than one dominant allele exists for a given gene
Term
incomplete dominance
Definition
when a heterozygote expresses a phenotype that is intermediate between the two homozygous gentoypes
Term
penetrance
Definition
a population measure defined as the proportion of individuals in the population carrying the allele who actually express the phenotype; full penetrance means 100% of people with the allele display the phenotype, nonpenetrance would be no indivduals with the allele show the phenotype
Term
expressivity
Definition

varying phenotypes despite identical genotypes

  • constant expressivity - all individuals with a given genotype express the same phenotype
  • variable expressivity - inviduals with the same genotype may have different phenotypes
Term
gene pool
Definition
all of the alleles in a given population
Term
transposons
Definition
elements that can insert and remove themselves from the genome
Term
chromosomal mutations
Definition
large scale mutations affecting whole segments of DNA
Term
duplication mutation
Definition
when a segment of DNA is copied multiple times
Term
inversion mutation
Definition
when a segment of DNA is reversed
Term
insertion mutation
Definition
when a segment of DNA is moved from one chromosome to another
Term
translocation mutation
Definition
when a segment of DNA is swapped with a segment of DNA from another chromosome
Term
genetic leakage
Definition
a flow of genes between species through hybrid offspring
Term
genetic drift
Definition
occurs when the composition of the gene pool changes as a result of chance; more pronounced in small populations
Term
founder effect
Definition
more extreme case of genetic drift in which a small population of a species finds itself in reproductive isolation from other populations
Term
bottlenecks
Definition
events that suddenly isolate a small population
Term
inbreeding depression
Definition
loss of genetic variation causing a reduced fitness of a population
Term
outbreeding or outcrossing
Definition
introduction of unrelated individuals into a breeding group
Term
test cross
Definition
the organism with an unkown genotype is crossed with an organism known to be homozygous recessive
Term
recombination frequency
Definition
the likelihood of two alleles being separated during corssing over in meiosis; a 0% percent recombination frequency means they never recombine and are very strongly linked
Term
allele frequency
Definition
how often an allele appears in a population
Term
Hardy-Weinberg principle
Definition

if the below criteria are met, then the allele frequencies will remain constant

  • the population is very large
  • there are no mutations that affect the gene pool
  • mating between individuals in the population is random (no sexual selection)
  • there is no migration of individuals into or out of the population
  • the genes in the population are all equally successful at reproducing
Term
Hardy-Weinberg equilibrium equations
Definition

where p and q are the frequency of two alleles, adding them together must equal 1 because they are the only two choices

  • p + q = 1

square both sides of the equation

  • p2 + 2pq + q2 = 1
p2 is the frequency of one homozygous genotype and q2 is the other. pq represents the heterozygous genotype. If the frequencies of these alleles stays the same from generation to generation a population is at Hardy-Weinberg equilibrium

 

Term
inclusive fitness
Definition
considers an organism's success to be based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others; survival of offspring or relatives ensures continuation of genes in subsequent generations
Term
punctuated equilibrium
Definition
considers evolution to be a very slow process with intermittent rapid bursts of evolutionary activity
Term
stabilizing selection
Definition
keeps phenotypes in a narrow range, excluding extremes
Term
directional selection
Definition
moves the average pehnotype toward one extreme
Term
disruptive selection
Definition
moves toward two different phenotypes at the extremes and can lead to speciation
Term
adaptive radiation
Definition
the rapid emergence of multiple species from a common ancestor, each of which occupies it own ecological niche decreasing competition for resources
Term
species
Definition
the largest group of organisms capable of breeding to form fertile offspring
Term
speciation
Definition
the formation of a new species through evolution
Term
isolation
Definition
when progeny of two populations can no longer freely interbreed
Term
prezygotic mechanisms vs postzygotic mechanisms
Definition
  • prevent formation of the zygote completely
  • allow for gamete fusion but yield either nonviable or sterile offspring
Term
divergent evolution
Definition
occurs when two species sharing a common ancestor become more different
Term
parallel evolution
Definition
occurs when two species sharing a common ancestor evolve in similar ways due to analogous selection pressures
Term
convergent evolution
Definition
occurs when two species not sharing a recent ancestor evolve to become more similar due to analogous selection pressures
Term
molecular clock model
Definition
the degree of difference in the genome between two species is related to the amount of time since the two species broke off from a common ancestor
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