Warm-up- hand this in for credit 1. Define evolution 2. Define natural selection. 3. What are the four components that are important in order for natural selection to occur? 4. The Hardy-Weinberg equilibrium equation is used to make predictions of allelic and genotypic frequencies for future generations. If a population in a future generation has allelic frequencies that do not match the predicted values, what does this mean? 5. You encounter a population in which there are 100 individuals. 25 of these individuals are homozygous dominant. A) what is the allele frequency for this dominant allele? B) What proportion of the next generation’s population should be heterozygous?

Evolution Change in allele frequencies in populations over time OR Change in genetic composition in a population from generation to generation (or over time)

Natural selection Process in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals without those traits

Key component of natural selection!! You must know this!! 1. Individuals in a population vary in traits 2. These traits must be heritable 3. Species can produce more offspring than their environment can support 4. Species with certain traits survive and reproduce at higher rates than those without those traits *Individuals do not evolve!! Only populations do! *Natural selection acts on individuals and leads to adaptive evolution!

You encounter a population in which there are 100 individuals You encounter a population in which there are 100 individuals. 25 of these individuals are homozygous dominant. A) what is the allele frequency for this dominant allele? B) What proportion of the next generation’s population should be heterozygous?

Homework 1) Page 491 List each type of reproductive barrier, explain it, and give an example. Due tomorrow 2) Read pp 488-492 3) essay #1 due this Thursday Typo!!!! Recheck the updated version!!!!!

The key component for evolution to occur is… Genetic variation!!

Genetic Variation Genetic variation among individuals is caused by differences in genes or other DNA segments Phenotype is the product of inherited genotype and environmental influences Natural selection can only act on variation with a genetic component

Variation Within a Population Both discrete and quantitative characters contribute to variation within a population Discrete characters can be classified on an either-or basis Example: color, shape, presence/absence of a phenotype Quantitative characters vary along a continuum within a population Example: body mass, litter size Discrete: color Quantitative: size

Sources of Genetic Variation New genes and alleles can arise by mutation or gene duplication Sexual reproduction produces genetic variation through crossing over, independent assortment, and fertilization

Alleles are different variations of a gene Genotypes are combination of alleles that an individual has, One allele came from parent 1, and other came from parent 2

Hardy-Weinberg Principle Allele frequencies of alleles and genotypes in a population will remain constant from generation to generation if all assumptions are met A gene pool that remains constant is said to be in Hardy- Weinberg equilibrium

AA Aa aa ? Generation 1 Generation 2

AA Aa aa ? Generation 1 Generation 2 p2 + 2pq + q2 = 1

Practice on your own : Write this in your notes. What are the genotypic frequencies? What are the allelic frequencies? If there are 700 cats in the next generation, how many of them should be homozygous recessive in the next generation? (assume HW equilibrium)

Cystic Fibrosis 1 The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers? about 0.04% about 2% about 4% The frequency cannot be calculated because selection violates Hardy- Weinberg assumptions. Answer: c The frequency of carriers is 2pq. The allele frequency, q, is 1/50 since qq = 1/2500. P is close to 1. You may want to discuss why option d does not apply. https://www.polleverywhere.com/multiple_choice_polls/kwbKA0IH4N9iz8I 18

Cystic Fibrosis 1 The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers? about 0.04% or about 2% or about 4% The frequency cannot be calculated because selection violates Hardy- Weinberg assumptions. Answer: c The frequency of carriers is 2pq. The allele frequency, q, is 1/50 since qq = 1/2500. P is close to 1. You may want to discuss why option d does not apply. 19

Assumptions of Hardy-Weinberg principle Allele frequencies in a population will remain constant if ALL of the following conditions are met: The population is infinitely large Individuals mate randomly No genetic migration No natural selection No mutation

Three main driving forces that cause changes in allele frequencies Natural selection Genetic drift Gene flow

1) Natural selection Process in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals without those traits Adapations are inherited traits that enhance organismal survival and reproduction in specific environments Fitness: measure of reproductive success associated with a particular trait

Natural selection is the only mechanism that consistently causes adaptive evolution Evolution by natural selection involves both chance and “sorting” New genetic variations arise by chance Beneficial alleles are “sorted” and favored by natural selection Only natural selection consistently results in adaptive evolution

Types of natural selection Directional Disruptive Stabilizing

Frequency of individuals Figure 23.13 Original population Frequency of individuals Phenotypes (fur color) Original population Evolved population Figure 23.13 Modes of selection. (a) Directional selection (b) Disruptive selection (c) Stabilizing selection

2) Genetic Drift- the reason why large population size is important for Hardy-Weinberg Equilibrium The smaller a sample, the greater the chance of deviation from a predicted result Genetic drift : when chance events cause allele frequencies to fluctuate unpredictably from one generation to the next Genetic drift tends to reduce genetic variation through losses of alleles

Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 CRCR Figure 23.9-1 CRCR CRCR CRCW CWCW CRCR CRCW CRCR CRCW Figure 23.9 Genetic drift. CRCR CRCW Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3

5 plants leave off- spring Figure 23.9-2 5 plants leave off- spring CRCR CRCR CWCW CRCR CRCW CRCW CWCW CRCR CRCR CWCW CRCW CRCW CRCR CRCW CWCW CRCR Figure 23.9 Genetic drift. CRCR CRCW CRCW CRCW Generation 1 Generation 2 p (frequency of CR) = 0.7 p = 0.5 q (frequency of CW) = 0.3 q = 0.5

5 plants leave off- spring 2 plants leave off- spring Figure 23.9-3 5 plants leave off- spring 2 plants leave off- spring CRCR CRCR CWCW CRCR CRCR CRCW CRCW CRCR CRCR CWCW CRCR CRCR CWCW CRCR CRCR CRCW CRCW CRCR CRCR CRCR CRCW CWCW CRCR CRCR Figure 23.9 Genetic drift. CRCR CRCW CRCW CRCW CRCR CRCR Generation 1 Generation 2 Generation 3 p (frequency of CR) = 0.7 p = 0.5 p = 1.0 q (frequency of CW) = 0.3 q = 0.5 q = 0.0

The Founder Effect The founder effect occurs when a few individuals become isolated from a larger population. Example: wind blows birds off course to another island Allele frequencies in the small founder population can be different from those in the larger parent population

The Bottleneck Effect The bottleneck effect is a sudden reduction in population size due to a change in the environment , ex: urbanization The resulting gene pool may no longer be reflective of the original population’s gene pool If the population remains small, it may be further affected by genetic drift

Figure 23.10-1 Figure 23.10 The bottleneck effect. Original population

Original population Bottlenecking event Figure 23.10-2 Figure 23.10 The bottleneck effect. Original population Bottlenecking event

Reduction in genetic variation via genetic drift!!! Figure 23.10-3 Reduction in genetic variation via genetic drift!!! Figure 23.10 The bottleneck effect. Original population Bottlenecking event Surviving population

Case Study: Impact of Genetic Drift on the Greater Prairie Chicken Loss of prairie habitat caused a severe reduction in the population of greater prairie chickens in Illinois The surviving birds had low levels of genetic variation, and only 50% of their eggs hatched

Greater prairie chicken Figure 23.11 Pre-bottleneck (Illinois, 1820) Post-bottleneck (Illinois, 1993) Greater prairie chicken Range of greater prairie chicken (a) Number of alleles per locus Percentage of eggs hatched Population size Location Illinois 1930–1960s 1993 1,000–25,000 <50 5.2 3.7 93 <50 Figure 23.11 Genetic drift and loss of genetic variation. Kansas, 1998 (no bottleneck) 750,000 5.8 99 Nebraska, 1998 (no bottleneck) 75,000– 200,000 5.8 96 (b)

Effects of Genetic Drift: A Summary Genetic drift is significant in small populations Genetic drift causes allele frequencies to change at random Genetic drift can lead to a loss of genetic variation within populations Genetic drift can cause harmful alleles to become fixed

3) Gene Flow Gene flow consists of the movement of alleles among populations Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen) Gene flow tends to reduce variation among populations over time Gene flow can decrease or increase the fitness of a population