1. Population Genetics
Combines Darwinian selection and Mendelian inheritance
Study of genetic variation within a population. 
Emphasis on quantitative characters.
                                   

2. Evolution acts on populations, not on individuals.
Population: individuals of the same species in an area.
All members of population can interbreed.
Share a Gene Pool: all the alleles (B, b) for all the traits in a population.

3.  If all members of a population are homozygous for a particular allele, then the allele is fixed in the gene pool.
--Usually, more than 2 alleles for a gene, each having a relative frequency =(proportion) in gene pool

4. How can we determine when population is evolving?
Use the The Hardy-Weinberg Theorem!
                       
H-W Describes a non-evolving population= The gene pool of a non-evolving population remains constant over multiple generations; i.e., the allele frequency does not change over generations of time.
Natural populations are not expected to actually be in Hardy-Weinberg equilibrium. 
Deviation from H-W equilibrium usually results in evolution.
Understanding a non-evolving population, helps us to understand how evolution occurs.

5. Assumptions of the H-W Theorem:
1.Large population size: small populations can have chance fluctuations in allele frequencies (e.g., fire, storm).
2.No migration: immigrants can change the frequency of an allele by bringing in new alleles to a population.
3.No net mutations: if alleles change from one to another, this will change the frequency of those alleles.
4.Random mating: if certain traits are more desirable, then individuals with those traits will be selected and this will not allow for random mixing of alleles.
5. No natural selection: if some individuals survive and reproduce at a higher rate than others, then their offspring will carry those genes and the frequency will change for the next generation.

6.                   The Hardy-Weinberg Equation:
                                    1.0 = p2 + 2pq + q organisms:                                               
p2 = frequency of AA genotype
2pq = frequency of Aa
q2 = frequency of aa genotype
1= p+q
For alleles: p=frequency of dominant allele=A
q=frequency of recessive allele=a

7. PTC: Genes and Bitter Taste
In 1931, a chemist named Arthur Fox was pouring some powdered PTC into a bottle. When some of the powder accidentally blew into the air, a colleague standing nearby complained that the dust tasted bitter. Fox tasted nothing at all.
Curious how they could be tasting the chemical differently, they tasted it again. The results were the same. Fox had his friends and family try the chemical then describe how it tasted. Some people tasted nothing. Some found it intensely bitter, and still others thought it tasted only slightly bitter.
The ratio of tasters to non-tasters varies between populations, but every group has some tasters and some non-tasters. On average, 75% of people can taste PTC, while 25% cannot.
PTC stands for phenylthiocarbamide. Also known as phenylthiourea, the chemical structure of PTC resembles toxic alkaloids found in some poisonous plants.

8. The PTC gene, TAS2R38, was discovered in 2003.
The ability to taste PTC (or not) is conveyed by a single gene that codes for a taste receptor on the tongue.
The PTC gene, TAS2R38, was discovered in 2003.
There are two common forms (or alleles) of the PTC gene, and at least five rare forms.
One of the common forms is a tasting allele, and the other is a non-tasting allele.
Each allele codes for a bitter taste receptor protein with a slightly different shape. The shape of the receptor protein determines how strongly it can bind to PTC.
Since all people have two copies of every gene, combinations of the bitter taste gene variants determine whether someone finds PTC intensely bitter, somewhat bitter, or without taste at all.

9. Although PTC is not found in nature, the ability to taste it correlates strongly with the ability to taste other bitter substances that do occur naturally, many of which are toxins.
Plants produce a variety of toxic compounds in order to protect themselves from being eaten.
The ability to discern bitter tastes evolved as a mechanism to prevent early humans from eating poisonous plants.
Humans have about 30 genes that code for bitter taste receptors. Each receptor can interact with several compounds, allowing people to taste a wide variety of bitter substances.
Studies indicate that individuals with the "strong tasters" PTC gene variant were less likely to be smokers. This may indicate that people who find PTC bitter are more likely than non-tasters to find the taste of cigarettes bitter and may be less likely to smoke.
Other studies suggest that there may be correlations between the ability to taste PTC and preferences for certain types of foods. This may be why some of us think that broccoli is just too bitter to eat.

10. * Approximately 75% of overall population can taste PTC.

13. Causes of microevolution:
Evolution within a species/population = microevolution=
=changes in allele frequencies in a gene pool from generation to generation.
Causes of microevolution:
                       
1)  Genetic drift (especially in small populations)
2) Natural selection
3) Gene flow
Mutation
5) Non-random mating

14. Genetic Drift - alteration of the gene pool
of a small population due to chance.
--a new population “drifts” away from original, and the new pop. Has a different allele freq.
2 main types: Bottleneck and Founder Effect

15. *disturbance removes large portion of the population.
       
Bottleneck effect
*disturbance removes large portion of the population.
*surviving population does not represent the allele frequency in the original population.
Ex. Northern elephant seals
“Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.”

17. Founder Effect:
-Colonization of new location by small # of original population changes allele freq. b/c individuals starting new pop. Differ in their genetic makeup
Ex. Dwarfism is much higher in a Pennsylvania Amish community due to a few German founders.
SA finches

18. Variation between populations
Geographic variations are differences between gene pools due to differences in environmental factors. 
Ex. Cline,
Ex. Insects and birds are larger in warmer climates (perhaps smaller body size conserves heat)

19. Cline Example

20. Variation within a population
Polymorphism
existence of two or more forms of a character (morphs), in high frequencies, within a population. 
Applies only to discrete characters.
Ex. Jaquar coloration
Most common example- sexual dimorphism

21. Diploidy and balanced polymorphism preserve variation
                       
a.  Diploidy often hides genetic variation from selection in the form of recessive alleles.
***Dominant alleles “hide” recessive alleles in heterozygotes- provides more possibilities for survival if survival conditions change
b.  Heterozygote advantage where the heterozygote has greater survival and reproductive success than either homozygote
(Example: Sickle cell anemia where heterozygotes –Aa- are resistant to malaria). AA- gets malaria, aa- gets sickle cell

23. - Example: human fingerprints.
Neutral variation is genetic variation that results in no competitive advantage to any individual.
                                   
- Example:  human fingerprints.

24. Sexual selection leads to differences between sexes
Sexual dimorphism is the difference in appearance between males and females of a species.
Competition among and between members of the same sex result in:
males most often having secondary sexual equipment such as antlers that are used in competing for females.
-sophisticated secondary sexual characteristics for fanciness
e.g., peacock feathers.