2. 13.8 The gene pool of a nonevolving population remains constant over the generations
Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool
p2 + 2pq + q2 or (homozygous dominant genotypes + heterozygous genotypes + homozyogous recessive genotypes) ** know for test (p + q = 1; p = dominant allele and q = recessive allele frequencies)
To test this, let’s look at an imaginary, non- evolving population of blue-footed boobies
Webbing
No webbing
Figure 13.8A

3. We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists
Phenotypes
Genotypes WW Ww ww
Number of animals (total = 500)
320
160 20
Genotype frequencies
320/500 = 0.64
160/500 = 0.32
20/500 = 0.04
Number of alleles in gene pool (total = 1,000)
640 W
160 W w
40 w
Allele frequencies
800/1,000 = 0.8 W
200/1,000 = 0.2 w
Figure 13.8B

4. Recombination of alleles from parent generation
W sperm
p = 0.8
W egg
p = 0.8
SPERM
EGGS WW
p2 = 0.64
w sperm
q = 0.2
w egg
q = 0.2 WW
qp = 0.16 Ww
pq = 0.16 ww
q2 = 0.04
Next generation:
Genotype frequencies
0.64 WW
0.32 Ww
0.04 ww
Allele frequencies
0.8 W
0.2 w
Figure 13.8C

5. Hardy-Weinberg practice

6. 13.9 Connection: The Hardy-Weinberg equation is useful in public health science
Public health scientists use the Hardy-Weinberg equation to estimate frequencies of disease-causing alleles in the human population
Example: phenylketonuria (PKU)
PKU occurs 1/10000 babies. Changes in the results demonstrate a potential issue if there is an increase in PKU occurrence.

7. 13.10 Five conditions are required for Hardy-Weinberg equilibrium
(H-W equilibrium rarely exists but )
The population is very large
The population is isolated (no migration of individuals, or gametes, into our out of the population
Mutations do not alter the gene pool
Mating is random
All individuals are equal in reproductive success (no natural selection or fitness differences)

8. 13.11 There are several potential causes of microevolution
Genetic drift is a change in a gene pool due to chance
The effect of a loss of individuals from a population is much greater when there are fewer individuals
Genetic drift can cause the bottleneck effect (results from a disaster reducing population size, i.e. elephant seals)
Original population
Bottlenecking event
Surviving population
Figure 13.11A

9. or the founder effect (colonization of an area by a small number of individuals) Think Galapagos Islands or The Mutiny on the Bounty and Fletcher Christiansen with native islanders
Figure 13.11B, C

10. Gene flow is gain or lose of alleles from population due to immigration or emigration
Mutations are rare but occur constantly. Never usually directly responsible for evolutionary change but provide raw material for which other mechanisms of microevolution work
Nonrandom mating is usually the case where choice of mater is important part of behavior but it does not typically change allele frequency or microevolution.
Reproductive success leads to adaptive changes in gene pool

11. 13.12 Adaptive change results when natural selection upsets genetic equilibrium
Natural selection results in the accumulation of traits that adapt a population to its environment
If the environment should change, natural selection would favor traits adapted to the new conditions
Amount and kind of genetic variation in population can limit the degree of adaptation.
Need to have the possible genes in the first place

12. 13.13 Variation is extensive in most populations
VARIATION AND NATURAL SELECTION
Variation is extensive in most populations
Phenotypic variation may be environmental or genetic in origin
But only genetic changes result in evolutionary adaptation
Variation of phenotypes due to attributes of polygenic inheritance or combination of multiple genes for a given trait.

13. Many populations exhibit polymorphism and geographic variation
Polymorphism = contrasting forms are present (often due to polygenic inheritance.
Geographic variation = based on environment
Stratification or clinal, smooth across population
To measure
Determine ave. percent of gene loci heterozygous
Determine nucleotide diverstiy of DNA sequences
Figure 13.13

14. 13.14 Connection: Mutation and sexual recombination generate variation
Parents A1 A1 A2 A3
Mutation is the ultimate source of all variation
MEIOSIS A1 A2 A3
Gametes
FERTILIZATION
Offspring, with new combinations of alleles A1 A2 A1 A3
and
Figure 13.14

15. Sexual recombination shuffles alleles in diploid organisms.
Mutations normally harmful but they may help organism’s adaptation with a changing environment
Sexual recombination shuffles alleles in diploid organisms.
Independent assortment
Crossing over
Random fertilization
Organisms reproducing sexually with longer life spans and sexual recombination necessary to increase the variation stemming from single mutations.

16. 13.15 Overview: How natural selection affects variation
Ancestral population is varied with characteristics suited for many environments
Over generations, individuals with best characteristics for environment leave more offspring
Natural selection tends to reduce variability in populations or less suited organisms produce less offspring
The diploid condition preserves variation by “hiding” recessive alleles. Not seen because with a dominant allele. May take many generations to get rid of disadvantageous recessive alleles

17. Balanced polymorphism may result from the heterozygote advantage
Heterozygote is favored over either homozgyote, so variation is maintained in the population.
i.e. sickle cell, heterozygote is immune to malaria but does not have trait. Homozygote dominant, no sickle cell and no immunity from malaria.

18. 13.16 Not all genetic variation may be subject to natural selection
Some variations show neutral variation, providing no apparent advantage or disadvantage
Example: human fingerprints
Frequency changes due to genetic drift, not natural selection
May be some unknown benefit
Figure 13.16

19. 13.17 Connection: Endangered species often have reduced variation
Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment
Studies have shown that cheetah populations exhibit extreme genetic uniformity
Thus they may have a reduced capacity to adapt to environmental challenges
Rosenberg connection SSP
Figure 13.17

20. Rosenberg connection SSP

21. Although inbreeding can reduce individual fitness and contribute to population extinction, gene flow between inbred but unrelated populations may overcome these effects. Among extant Mexican wolves (Canis lupus baileyi), inbreeding had reduced genetic diversity and potentially lowered fitness, and as a result, three unrelated captive wolf lineages were merged beginning in We examined the effect of inbreeding and the merging of the founding lineages on three fitness traits in the captive population and on litter size in the reintroduced population. We found little evidence of inbreeding depression among captive wolves of the founding lineages, but large fitness increases, genetic rescue, for all traits examined among F1 offspring of the founding lineages. In addition, we observed strong inbreeding depression among wolves descended from F1 wolves. These results suggest a high load of deleterious alleles in the McBride lineage, the largest of the founding lineages. In the wild, reintroduced population, there were large fitness differences between McBride wolves and wolves with ancestry from two or more lineages, again indicating a genetic rescue. The low litter and pack sizes observed in the wild population are consistent with this genetic load, but it appears that there is still potential to establish vigorous wild populations.

22. 13.18 The perpetuation of genes defines evolutionary fitness
An individual’s Darwinian fitness is the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals
Production of fertile offspring is the only score that counts in natural selection

23. 13.19 There are three general outcomes of natural selection
Original population
Frequency of individuals
Phenotypes (fur color)
Original population
Evolved population
Stabilizing selection
Directional selection
Diversifying selection
Figure 13.19

24. Explaining outcomes
Stabilizing selection – narrows the range of population variability towards intermediate form. Usually occurs in stable environment
Directional selection – moves from toward one of the extremes. Usually occurs during environmental change
Diversifying selection – environmental conditions vary where both extremes favored over intermediate

25. 13.20 Sexual selection may produce sexual dimorphism
Sexual selection leads to the evolution of secondary sexual characteristics
These may give individuals an advantage, look bigger, stronger in mating (and disadvantage, easier for predator to see)
Figure 13.20A, B

26. 13.21 Natural selection cannot fashion perfect organisms
This is due to:
historical constraints – can’t restart just because need for change
adaptive compromises, one adaption might be advantage or later a disadvantage
chance events, organism depends on nature, not usually the other way around.
availability of variations, can’t change to something better if no genetic foundation to draw from – may result in extinction

27. Movie: Desire
Questions?

28. Connection: The evolution of antibiotic resistance in bacteria is a serious public health concern
The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria
Example: Mycobacterium tuberculosis
Figure 13.22