darwin couldnt explain...
1. the source of genetic variation
2. how traits were passed from parent to offspring
gene pools
combined genetic info of all the members of a particular population
gene pools usually have...
two or more alleles
relative frequency
equals the number of times an allele occurs in a gene pool compared to number of times other alleles occur
mutations
random changes in genes or chromosomes
gene shuffling
pairing of one chromosome from mom and one from dad for each of 23 chromosome pairs can have > 8 million gene combos
crossing over in meiosus leads to more...
variation
examples of single-gene traits
widows peak, dimples, hitchhikers thumb
examples of polygenic traits
eye color, skin color, hair color
polygenic traits
traits controlled by two or more genes
natural selection acts on...
phenotypes
relative frequencies of alleles change in a population by alleles being added/subtracted from a population by...
1. dying w/o reproducing
2. having a lot of offspring
genetic definition of evolution
any change in relative frequencies of alleles in a populations gene pool
when will natural selection on single-gene traits lead to evolution?
when the relative frequencies of the alleles change
what makes the relative frequencies of alleles change?
allele might disappear, increase, or remain unchanged
directional selection
push toward one end of bell curve
stabilizing selection
middle of curve has higher fitness
disruptive selection
upper/lower end of curve are more fit and middle values disappear
hardy-weinberg equilibrium
allele frequencies in a population will stay the same unless one or more factors causes change to take place
are there cases where evolution does not occur?
yes, but very rare
5 conditions to maintain genetic equilibrium
1. random mating
2. large populations
3. no movement in/out of population
4. no mutations
5. no natural selection
for a new species to form what must you have?
reproductive isolation
reproductive isolation
organisms aren't able to breed with each other
behavioral isolation
courtship dances; nest sites; mating calls
geographical isolation
mountains, rivers; once separated, adapt to new environment; cant mate with original population
temporal isolation
time
6 steps of speciation
1. founders arrive
2. separation of populations
3. changes in gene pool
4. reproductive isolation
5. ecological competition
6. continued evolution
when are two species said to be reproductively isolated?
when they cannot interbreed and produce fertile offspring
genetic drift
random change in allele frequency
when is genetic drift more likely to occur?
in small populations
speciation
formation of new species
what kind of isolation occurs when two populations are capable of interbreeding but have differences in courtship rituals or other types of behavior?
behavioral isolation
the founder effect
when allele frequencies change as a result of the migration of a small subgroup of a population
two populations kept separate by a river are said to be in...
geographic isolation
what kind of isolation occurs when two or more species reproduce at different times?
temporal isolation