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a group of similar organisms who have the potential to interbreed to produce fertile offspring.
all members of a single species in same place at same time
diversity as allele frequencies.
changes in allele frequencies
species change from one species to another
changes in allele frequencies within a population
all alleles of the population.
the emergence of numerous species from a common ancestor
(p2 + 2pq + q2 = 1.0); used to measure changes in gene frequencies over time within a population
frequency of the homozygous dominant genotype within gene pool
frequency of the heterozygous genotype within gene pool
frequency of the homozygous recessive genotype within gene pool
gene frequency calculation
to determine gene frequency, calculate its percent from the total number of alleles in the population
there are 100 wolves
the frequency of the G allele is .6
how many wolves are grey?
- p + q = 1 so q is .4
- p2 + 2pq + q2= 1.0
- q2 is the number of white wolves, p2 is number of dominant grey wolves, so p2+ 2pq will be the total number of grey wolves (2pq is heterozygous so those wolves will be grey)
- p2= .36
- 2pq = 2 (.6*.4) =2(.24) = .48
- .36 + .48 = .84; so 84 wolves are grey
Hardy-Weinberg equation predicts that no change (evolution) will occur in a population if the following five conditions are met
- (1) Mating is random.
- (2) The population is isolated (no gene flow)
- (3) no natural selection
- (4) Mutations do not alter the gene pool.
- (5) The population is large.
agents of evolutionary change
- 1. natural selection
- 2. genetic drift
- 3. mutation
- 4. gene flow
- 5. non-random mating
the mechanism that brings about adaptation to the environment as evolution occurs
a change in gene frequencies due to sampling error. In actual populations this may be due to the "founder effect" or after a disaster the "bottleneck effect".
changes in the genetic code
gain or loss of genes from a gene pool due to movement of individuals
a small population is more apt to undergo genetic drift- high allele frequency changes by chance
occurs when a majority of genotypes are prevented from participating in the production of the next generation due to extreme natural or human interference
3 types of natural selection
- stabilizing selection
- directional selection
- disruptive selection
- occurs when an intermediate phenotype can improve the adaptation of the population to those aspects of the environment that remain constant. the intermediate phenotype is favored
- ex. human birth weight; infants with intermediate weight have better chance at survival
- occurs when an extreme phenotype is favored, and the distribution curve shifts in that direction. changes the average phenotype of a population over time
- ex. the modern horse shows a gradual increase in body size as the environment changed from forest to grassland
- found when two ore more extreme phenotypes are favored over any intermediate phenotype
- ex. snails have wide habitat range; in low vegetation light banded snails are more prevalent, in forested areas, dark shells are more prevalent: so there are 2 distinct phenotypes in the population
Theory of Punctuated Equilibrium
- proposed by Stephen Jay Gould and Niles Eldridge;
- suggests that evolution may be characterized by abrupt "starts and stops"; species may remain unchanged for long periods of time and then experience rapid evolution perhaps stimulated by catastrophic events;
- as opposed to Darwin's gradualistic model of evolution.
Morphological (structural) traits
diagnostic traits: distinct physical characteristics
A common ancestor for two or more different groups. It does not rely only on morphology to define a species
reproductive isolating mechanisms
- inhibit gene flow
- 2 types: prezygotic and postzygotic
prezygotic isolating mechanisms
- Habitat Isolation: 2 species separated by physical barrier
- Temporal Isolation: 2 species live in same area but don’t mate at the same time
- Behavioral Isolation: rituals that prevent one species from mating with another
- Mechanical Isolation: reproductive structure or other parts prevent mating
- Gamete Isolation: the gametes are incompatible; sperm wont get to the egg, or cant penetrate the egg, the egg may not recognize the sperm
Postzygotic Isolating Mechanisms
- Postzygotic Isolating Mechanisms; if the zygote has formed
- hybrid inviability: zygote not viable; dies
- hybrid sterility: sterile adult
making a species
- new species result because of geographical barriers
- adaptive radiation is a type of allopatric speciation
- allo-away, patric- country
- species develops without geographical barrier
- one population develops into two or more with genetic variation
- polyploidy is a type of sympatric speciation in plants
similar trait evolves into two unrelated species as a result of exposure to similar enviroments