chapter 17 Flashcards
all the alleles of all the genes in a population; “genetic resources,” shared by all the members of the population (in theory)
the gene pool
infrequent but inevitable changes in genes
mutations
mutation is a source of…
new alleles/genetic variation
crossing over at meiosis i introduces…
new combinations of alleles into chromosomes
independent assortment at meiosis i mixes…
maternal and paternal chromosomes
fertilization combines…
alleles from two parents
changes in chromosome number or structure occur which are known as…
transposition, duplication, or loss of chromosomes
individuals do not evolve, ______________ do
populations
frequency of certain ________ is the result of evolution
traits
a theoretical state in which an allele’s frequency never changes in a population’s gene pool
genetic equilibrium (population is not evolving)
list the five conditions needed for genetic equilibrium
- mutations never occur
- mating is random
- the allele does not affect survival or reproduction (i.e., there is no selection for or against that trait)
- the population is infinitely large
- no immigration or emigration
when comparing a population’s gene pool to a control group, the “null hypothesis” is the population at…
genetic equilibrium
at genetic equilibrium, proportions of genotypes at a locus with two alleles will remain the same
hardy-weinberg law
what does the hardy-weinberg law/equation state?
p^2 + 2pq + q^2 = 1
heterozygous genotypes for genetic diseases are known as “__________” for that disease, but remain unaffected themselves
carriers
small scale changes (small group, short time) in allele frequencies that drive a population away from genetic equilibrium
microevolution
the four main components of microevolution are…
- mutation
- natural selection
- genetic drift
- gene flow
a difference in the survival and reproductive success of different phenotypes, not purposeful, it simply fills the nooks and crannies of opportunity
natural selection
natural selection acts _________ on phenotypes and ___________ on genotypes
directly, indirectly
a type of selection where one end of the spectrum of phenotypes is favored
directional selection
a type of selection where the middle ground or “medium” phenotype is favored (extremes are NOT favored)
stabilizing selection
a type of selection where the extreme phenotypes are favored and (the middle is NOT favored)
disruptive selection
example of directional selection
peppered moths: coloration before, during, and after the industrial revolution
example of stabilizing selection
birth weight and mortality rates
example of disruptive selection
the beaks of birds with two types of seeds available (finches?)
a type of selection that is due to nonrandom mating; leads to sexual dimorphism
sexual selection
the term for different sexes having different traits
sexual dimorphism
the term for the change in the frequency of an existing gene variant in a population due to random chance
genetic drift
genetic drift is more prominent in __________ populations
small
when alleles disappear and leave only one possible form of that gene left, it’s known as
fixation
an effect that is due to a reduction of population size that is so severe it reduces genetic diversity
the bottleneck effect
an example of the bottleneck effect
elephant seal population was hunted down to 14-20 individuals, and is now at 130,000. electrophoresis revealed that there is now no allele variation at 24 genes
an effect pronounced on isolated islands; when a small group of individuals start a new population and their gene pool overall differs a lot from the original
the founder effect
island chains offshore that are prone to speciation
archipelagos
colonization and genetic divergence lead to…
speciation
examples of archipelagos
the galapagos, the hawaiian islands
in absence of other bird species on the hawaiian islands, ____________ radiated to fill numerous niches
honeycreepers
hawaii is home to ___% of fruit fly species
40
an effect that tends to keep the gene pools of populations similar; counters the differences that result from mutation, natural selection, and genetic drift
gene flow
