Evolution of Populations. Chapter 17

Transcription

1 Evolution of Populations Chapter 17

2 17.1 Genes and Variation i. Introduction: Remember from previous units. Genes- Units of Heredity Variation- Genetic differences among individuals in a population. New variation stems from random mutation

3 Variation takes two forms in populations Phenotypic Variation: Physical variation we can see Genotypic Variation: Genetic variation that s encoded in one s DNA genes. ex. Finch beaks ex. Sickle Cell distribution

4 A. Genetics Joins Evolutionary Theory 1. Genotype and Phenotype in Evolution a. Natural Selection acts upon individual s phenotypes, not genotypes. i. Ex. Finch beaks and available resources b. Phenotypes can be adaptations c. Carriers still possess dominant phenotype

5 Example: Albinism in prey The albino gene itself doesn t hurt the organism However, the phenotype makes it easy for predators to see them

6 A. Genetics Joins Evolutionary Theory Cont. 2. Populations and Gene pools a. Population- group of individuals of the same species in a defined area Why defined: Human population.

7 A. Genetics Joins Evolutionary Theory Cont. b. Gene Pool - consists of all the genes in a population, including different alleles for each gene

8 A. Genetics Joins Evolutionary Theory Cont. C. Allele Frequency: The Number of times an allele occurs in a gene pool. Example > Out of the 25 individuals The brown allele occurs 29 times 29/50=.58 or 58% The black allele occurs 21 times 21/50=.42 or 42%

9 B. Sources of Genetic Variation 1. Mutations: any change in the genetic material a. Random events b. Can be beneficial, neutral, or detrimental c. Ultimate source of all variation

10 Beneficial Mutations Unbreakable bones Lactose Tolerance Heterozygous sickle cell prevents malaria

11 Sources of Genetic Variation cont. 2. Genetic recombination in sexual reproduction a. Sexual reproduction uses both parents DNA b. Crossing over in meiosis = more variation in offspring c. Makes each child unique

12 Crossing over during meiosis Chromosomes swap bits of DNA After meiosis, gametes are formed 23 different chromosome pairs with 10,000 s of genes = lots of variation

13 Sources of Genetic Variation cont. 3. Lateral Gene Transfer a. Transferring genes from one organism to another b. Occurs with single cell organisms Conjugation

14 C. Single-Gene and Polygenic Traits 1. Single-Gene Traits: traits controlled by only one gene a. Creates two phenotypes b. Trait is present or it s not

15 Graphing Single-Gene Traits

16 Single-Gene and Polygenic Traits Cont. 2. Polygenic Traits: Traits controlled by many genes a. Many phenotypes b. Varies from one extreme to the other. c. Ex- Height, skin color,

17 Graphing Polygenic Traits Creates bell curve pattern Most individuals fall somewhere in the middle Very few are on either extreme

18 17.1 daily quiz Name: 10 pts, 2pts each Date: Per: 1. Traits that are controlled by many genes 2. What is the ultimate source of variation? 3. Does natural selection act on an individual s genotype or their phenotype (think about albinism) 4. What kind of curve on a graph do polygenic traits have? 5. I have gene pool of 10 alleles, 6 alleles are for black fur, 4 are for brown fur. What is the Allele frequency for black alleles?

19 Evolution as Genetic Change in Populations Chapter 17.2

20 A. How Natural Selection Works 1. Natural Selection on Single-gene traits a. N.S. can change allele frequencies b. Only fit organisms pass on genes Albinism

21 A. How Natural Selection Works Cont.

22 A. How Natural Selection Works Cont. 2. Natural Selection on Polygenic Traits: 3 types All three reduce variation within a population

23 a. Directional selection Selection begins to favor one extreme over another. Ex. Bigger beaks of finches.

24 b. Stabilizing Selection Selection against the extremes Mean becomes more common Ex. size of infants

25 c. Disruptive Selection Selection against the intermediate traits Favors extremes Ex: camouflage

26 B. Genetic Drift Genetic Drift: Random change in allele frequency Two types: Founder effect: Few individuals colonize a new area Bottleneck effect: Random event changes allele frequency Ex. natural disaster, disease Affect small populations!!!!!

27 Founder effect Individuals do not carry all of population s variation Only carry genes they inherited

28 Bottleneck Effect

29 C. Evolution versus Genetic Equilibrium Genetic Evolution: allele frequencies change over time Allows for change and variation Genetic Equilibrium: allele frequencies stay constant Populations stay the same

30 2. Hardy-Weinberg Principle Asked what prevents evolution? 5 factors to evolution 1. Nonrandom mating: Sexual selection, choosing your mate based off of desired traits 2. Small populations: Genetic drift affects heavily

31 Hardy-Weinberg Principle 3. Migration: Immigration: new genes coming in gene pool Emmigration: genes leaving gene pool 4. Mutations: new traits 5. Natural Selection: favored traits stay, unfavored are lost

32 Movement of genes in a population Increases variation Mutation Immigration Decreases variation Nonrandom mating Natural Selection Small population size Emmigration

33 The End

34 Daily Quiz Name: 17.2 Date: Per: 1. What is the word for individuals leaving a population? Hint: type of migration 2. Is genetic drift random or nonrandom? 3. When a group splits off from ancestral population and forms new population 4. What is it called when allele frequencies do not change over generations 5. Type of selection that favors the extremes of a population

35 The Process of Speciation Chapter 17.3

36 Speciation: Terms to know Species: A population, or group of populations, whose members can interbreed and produce fertile offspring Speciation: Formation of new species from an existing one. Reproductive Isolation: When two populations no longer interbreed

37 A. Isolating Mechanisms 1. Behavioral Isolation: Mating does not occur due to different mating behaviors a. Only identify members of the same species b. Behaviors species specific Fireflies have specific flashes depending on species

38 A. Isolating Mechanisms cont. 2. Geographic Isolation: Two population separated by a geographic barrier a. Do not have physical access b. Change over time

39 Kaibab Squirrel Albert s Squirrel Grand Canyon

40 A. Isolating Mechanisms cont. 3. Temporal Isolation: Species reproducing at separate times a. Allows species to decrease competition b. Hybrids still possible, not likely American Toad: reproduces in early summer Fowler s Toad: reproduces late summer

41 Things to take away Speciation leads to all new species Driven by the mechanisms of Evolution Result of species adapting to environments

42 The End

43 Daily Quiz! Name: 17.3 Date: Per: 1. The formation of new species is called? 2. Mechanism of isolation due to physical barriers separating two populations 3. What is it called when two species reproduce at separate times? 4. Form of isolation due to different courtship (mating) rituals 5. The Grand Canyon separates two species of what type of animal? Name that animal

44 Molecular Evolution 17.4

45 Molecular Clues: Introduction We know that genes change over time Changes are called mutations How can we measure change using DNA?

46 A. Molecular Clocks 1. Molecular clock a. Definition: using mutation rates in DNA to estimate when 2 species began evolving separately.

47 A. Molecular clocks cont. 2. Neutral mutations as ticks a. pos. and neg. mutations are affected by N.S. b. Neutral mutations happen unnoticed c. These appear at a similar rates in two species

48 A. Molecular clocks cont. 3. Calibrating the Clock a. Not easy to to use b. Each genome has multiple clocks, with different rates c. Compare rates of mutation across species

49 B. Gene Duplication 1. Copying genes a. Early organisms had little genetic material b. Humans: ~25,000 working genes c. Due to errors in crossing-over Unequal swapping of genes Some chromosomes grow longer, have more genes

50 B. Gene Duplication Cont. 2. Duplicate Genes evolve a. Duplicate genes can evolve separately b. Change without affecting original gene

51 B. Gene Duplication Cont. 3. Gene Families a. Group of related genes b. Ex. hox genes, globin genes

52 C. Developmental Genes and Body Plans 1. Hox Genes and Evolution a. Control which parts develop and where b. In insects and humans last common ancestor 500 mya c. Small changes have big results One change in the Ubx hox gene

53 The End