Chpt. 25 Evolutionary Processes

Front 1

Four Mechanisms that shift allele frequencies in populations

Back 1

1)Natural Selection - increases frequ. of alleles for adaptive traits
2)Genetic Drift - random changes in allele frequ.
3)Gene Flow - affect of migration on allele frequencies
4)Mutation - continually introduces new alleles

Front 2

Four Mechanisms that shift allele frequencies in populations

Back 2

1)Natural Selection - increases frequ. of alleles for adaptive traits
2)Genetic Drift - random changes in allele frequ.
3)Gene Flow - affect of migration on allele frequencies
4)Mutation - continually introduces new alleles

Front 3

gene pool

Back 3

novel approach to analyzing mating within populations - Hardy-Weinberg 1908
-holds all gametes produced in each generation of a population

Front 4

Hardy-Weinberg Principle

Back 4

two fundamental claims:
1)If the frequencies of A1 and A2 in a population are given by p and q, then the frequencies of the genotypes A1A1, A1A2, and A2A2 will be given by p2, 2pq, q2 for generation after generation
2)When alleles are transmitted according to the rules of Mendelian inheritance, their frequencies do not change over time. For evolution to occur, some other factor has to come into play

Front 5

Five conditions of Hardy-Weinberg Principle

Back 5

1)No natural selection
2)No genetic drift/random changes in allele frequ.
3)No gene flow
4)No mutation
5)Random Mating

Front 6

Analysis of Genotype Frequency according to Hardy-Weinberg Principle

Back 6

1)Estimate genotype frequ. by observation
2)Calculate obsered allele freq. from genotype freq. (M=frequ of MM + half MN)
3)Use observed allele frequ. to calculate genotype expected (p2+2pq+q2=1; p+q=1)
4)Compare observed and expected values

Front 7

Use of Hardy-Weinberg Principle

Back 7

Used to test the hypothesis that currently no evolution is occuring at a particular gene (null hyp), and that in the previous generation mating was random w/respect to the gene in question (doesn't mean selective forces haven't been at play in the past)

Front 8

Both-and Rule

Back 8

-"multiplication rule"
-the probability that two independent events will occur together
i.e. the probability of rolling two 6's: the probability of rolling a 6 for one die is 1/6 and independent of the other die. 1/6X1/6 =1/36
-same as with gametes

Front 9

Either-or Rule

Back 9

-"additon rule"
-the probability of an event happening where there are several ways for the event to occur.
-the probability is the sum of the probabilities of each way the event can occur
i.e. the probability of getting an Rr genotype from heterozygous parents:
1) prob of gettings R from father and r from mother: 1/2X1/2=1/4
2) prob of getting r from father and R from mother: 1/2X1/2=1/4
1/4+1/4=1/2

Front 10

Types of Natural Selection

Back 10

-balancing selection (heterozygote advantage)
-directional selection
-purifying selection
-stabilizing selection
-disruptive selection

Front 11

balancing selection

Back 11

AKA heterzygote advantage
-heterozygotes have a higher fitness than homozygotes
-maintains genetic variation in populations
i.e. HLA genes in humans, females who's genotype matches males (leads to homozygote offspring) have more trouble getting pregnant (heterzygote baby more fit)

Front 12

directional selection

Back 12

-Changein Avg Value - allele frequencies change in one direction
-tends to reduced genetic diversity of pop. (favored alleles increase to 1.0-fixed, and unfavored decrease to 0.0-lost)
i.e. Bigger birds have more insulation to survive cold and lack of food than smaller birds
-BUT opposing patterns of directional selection help maintain genetic variation "fitness trade-off" (big birds survive cold, but small birds are faster and make comeback)

Front 13

purifying selection

Back 13

-when disadvantageous alleles decline in frequency
-usually goes along w/directional selection and stabilizing selection

Front 14

Stabilizing selection

Back 14

-Reduction in Variation - no change in the average value of a trait over time, genetic variation reduced
-low fitness at each end of bell curve
i.e.Birthweight (tiny babies and huge babies less fit)

Front 15

Disruptive Selection

Back 15

-Increases Variation-elminates phenotypes near average value and favors extremes
-overall amount of genetic variation population is maintained
-somtimes plays a role in speciation
i.e.long beaks and short beaks are high fitness (only small and big seeds available)