Chapter 16 Population Genetics and Speciation
Variation of Traits • In nature many quantitative traits in a population tend to follow a bell curve pattern • Average (ex height and weight)
The report, Mean Body Weight, Height, and Body Mass Index (BMI) 1960-2002: United States, shows that the average height of a man aged 20-74 years increased from just over 5'8" in 1960 to 5'9½" in 2002, while the average height of a woman the same age increased from slightly over 5'3" 1960 to 5'4" in 2002. • Meanwhile, the average weight for men aged 20-74 years rose dramatically from 166.3 pounds in 1960 to 191 pounds in 2002, while the average weight for women the same age increased from 140.2 pounds in 1960 to 164.3 pounds in 2002.
Causes of Variation • Environment • heredity • Mutation • Recombination of genes • Random pairing of gametes
Theoretically…how many genetically unique, brothers and sisters could your parents produce? • For humans, the number of different gametes is 223 * 223, or 8,388,6082, giving 70,368,744,177,664 (70 trillion) possible combinations.
The Gene Pool • Total genetic information available in a population • Ex. In a homogeneous population like in South Korea….the dark skin alleles are just not in that gene pool.
Calculate Allele frequency ? • Divide number of certain allele by the total number of alleles
Phenotype frequency- number of individuals with a particular phenotype divided by the total number of individuals in the population • Frequency of a pair? Multiply the individual frequency numbers….
Hardy & Weinberg • Genotype frequencies tend to remain the same in a population unless acted on upon outside forces. (genetic equilibrium) • 5 things must happen for this to occur…
No Mutations • No individuals enter of leave • Population is large • Mating is random • Natural Selection does not occur *** Where on Earth does this happen?
Hardy Weinberg Equation • Calculate frequencies of alleles in population • P dominant allele • Q recessive allele • Problems 1, 2, 3 – go over together
Disrupting Genetic Equilibrium • Mutation: • Can increase with mutagens • Spontaneous mutations • Usually remain fairly low in number • Introduce new alleles into pop. • Many are harmful, some are beneficial some are neither
Mutations • Provide new alleles in gene pool • Adaptations
Gene Flow • Emigration- out • Immigration- in • This maintains gene flow • Ex.- Male lions chase away maturing cubs, they must go find another group… (This way we can be sure that the will not mate with their sister cubs…) • Gene flow….
Genetic Drift • Allele frequencies change as a result of random events… • This is more applicable to a smaller population than to a larger one.
Causes of Evolution • Genetic Drift: change due to chance • Bottleneck effect (fire, earthquake, flood)…
An example of a bottleneck: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.
Another bottleneck ex. Ashkenazi Jews population reduced due to Genocide (perhaps) and high incidence of Tay Sachs Disease now….
Non random mating • Not good • Geographic proximity • Amplify certain traits • Some select mates based on similarities, this is assortative mating…
Small population breaks away from a larger one. Rarer alleles are over represented….. • Amish 1770’s German population, extreme isolation, and intermarriage…
Sexual Selection • Females choose males, based on certain traits • Peacock: Male is brightly colored (may attract predators, but gets the girls to notice him ….)
Sexual Selection • sexual dimorphism: Differences between the females and males • “It bestows upon the females a large, pink, pillowy buttocks “
Natural Selection • Some members are more likely to survive and reproduce- thus their genes will be passed on to the next generation • When Natural Selection is at work, distribution of properties may change over time
Stabilizing Selection • It’s Best to have the average traits • The ones that survive are let’s say, “not the biggest , or the smallest”
Types of Selection • Stabilizing
Disruptive Selection • Being one extreme or another is better than being average
Directional Selection • One extreme form of a trait is better for survival
The story of the peppered moth in England during the Industrial Revolution…What type of selection is demonstrated here?
Formation of Species • Is called speciation • Over time animals can change a lot, or a little, from ancient ancestors
Morphological Concept of Species • Says…species are animals that look alike • Over time, we found that dissimilar animals bred and interacted in nature so we had to change that..
Biological Concept of Species • Species are members that can interbreed…
Modern Concept of Species? • Look alike • And, can interbreed