Essen%al knowledge standards 1.A.1: Natural selec/on is a major mechanism of evolu/on 1.A.2: Natural selec/on acts on phenotypic varia/ons in

Transcription

1 Essen%al knowledge standards 1.A.1: Natural selec/on is a major mechanism of evolu/on 1.A.2: Natural selec/on acts on phenotypic varia/ons in popula/ons 1.A.3: Evolu/onary change is also driven by random processes 3.C.1: Changes in genotype can result in changes in phenotype 4.C.3: The level of varia/on in a popula/on affects popula/on dynamics 4.C.4: The diversity of species within an ecosystem may influence the stability of the ecosystem

2 FLT I will be able to: Explain why the majority of point muta%ons are harmless Explain how sexual recombina%on generates gene%c variability List and describe the five condi%ons of Hardy- Weinberg equilibrium Apply the Hardy-Weinberg equa%on to a popula%on gene%cs problem Explain the role of popula%on size in gene%c drif By comple1ng Ch. 23 Lecture Notes

3 Ch. 23: The Evolu/on of Popula/ons

4 Modes of natural selec%on 4

5 Normal Distribu%on Defini1on: A bell-shaped curve. Medium traits have the highest frequency, & extreme traits have the lowest. A popula1on follows a normal distribu1on when: that popula/on is NOT under natural selec/on for the trait 5

6 6

7 VI. Adap%ve Evolu%on C. Modes of Natural Selec%on 1. Stabilizing Selec%on 2. Direc%onal Selec%on 3. Diversifying Selec%on (AKA Disrup%ve Selec%on) 7

8 8

9 VI. Adap%ve Evolu%on C. Modes of Natural Selec%on 1. Stabilizing Selec/on = favors intermediate phenotypes and acts against extreme phenotypes Example: Baby size Size of gall fly galls 9

10 10

11 11

12 12

13 VI. Adap%ve Evolu%on C. Modes of Natural Selec%on 2. Direc/onal Selec/on = favors individuals at one end (extreme) of the phenotypic range. What it looks like: Normal curve shifed to the right or lef Example: Drug-resistance in bacterial popula/ons Giraffe s necks gexng larger 13

14 14

15 15

16 VI. Adap%ve Evolu%on C. Modes of Natural Selec%on 3. Diversifying Selec/on (AKA Disrup/ve Selec/on) = favors individuals at both extremes of the phenotypic range Example: Some fur/body coloring Finch beaks 16

17 17

18 18

19 19

20 Frequency of individuals Natural Selec%on Original popula/on Original popula/on Evolved popula/on Phenotypes (fur color) (a) Direc/onal selec/on (b) Disrup/ve selec/on (c) Stabilizing selec/on

21 21

22 22

23 How does evolu%on occur? 23

24 24

25 25

26 26

27 27

28 28

29 Hardy-Weinberg Equilibrium: How do popula%ons evolve? 29

30 Background Gene/c Equilibrium = When popula/ons are NOT evolving Hardy-Weinberg Equilibrium: Genotype frequencies in a population stay the same over time 30

31 5 Condi/ons Required to be in No mutations Equilibrium 31

32 5 Condi/ons Required to be in Random Mating Equilibrium 32

33 5 Condi/ons Required to be in Equilibrium No natural selection 33

34 5 Condi/ons Required to be in Equilibrium Very large population 34

35 5 Condi/ons Required to be in No gene flow Equilibrium 35

36 II. Hardy-Weinberg Principle 3. H-W Equa%on The frequency of an allele in a popula%on can be calculated If there are 2 alleles at a locus, p and q are used to represent their frequencies The frequency of all alleles in a popula%on will add up to 1: p + q = 1 36

37 II. Hardy-Weinberg Principle 3. H-W Equa%on The Hardy-Weinberg principle describes an ideal popula%on that is not evolving. The closer a popula%on is to the criteria of the Hardy-Weinberg principle, the more stable the popula%on is likely to be. Calcula%ng Genotype Frequencies p 2 + 2pq + q 2 = 1 where p 2 and q 2 represent the frequencies of the homozygous genotypes and 2pq represents the frequency of the heterozygous genotype. 37

38 Hardy-Weinberg Equation p 2 + 2pq + q 2 = 1 AND p+q = 1 What it means: p = frequency of dominant allele A q = frequency of recessive allele a p 2 = frequency of AA individuals (dominant homozygotes) 2pq = frequency of Aa individuals (heterozygotes) q 2 = frequency of aa individuals (recessive homozygotes) 38

39 39

40 II. Hardy-Weinberg Principle Example: Let s say the allele for black coat is recessive. Calculate q 2 : 40

41 II. Hardy-Weinberg Principle Example: Let s say the allele for black coat is recessive. Calculate q 2 : 4/16 =

42 II. Hardy-Weinberg Principle Example: Let s say the allele for black coat is recessive. Now calculate q: 42

43 II. Hardy-Weinberg Principle Example: Let s say the allele for black coat is recessive. Now calculate q: Take the square root of 0.25 =

44 II. Hardy-Weinberg Principle Example: Now calculate p: 44

45 II. Hardy-Weinberg Principle Example: Now calculate p: Since p + q = 1, then p = 1, so p =

46 II. Hardy-Weinberg Principle Example: Finally, determine the frequency of heterozygotes in the popula%on: 46

47 II. Hardy-Weinberg Principle Example: Finally, determine the frequency of heterozygotes in the popula%on: 2pq = heterozygote frequency = 2(0.5) (0.5) = 0.5 (50% of the popula1on) 47

48 Do-Now In a certain popula%on of 1000 fruit flies, 640 have red eyes, while the remainder have sepia eyes. Sepia is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color? 48

49 1000 flies à 640 red-eyed à sepia is recessive. How many individuals would you expect to be homozygous for red eye color? Solu=on: ALWAYS CALCULATE Q 2 FIRST (since both p 2 and 2pq could be red-eyed) Sepia = recessive = q 2 Since = 360 à 360 flies have sepia eyes 360/1000 = 0.36 = q 2 Thus sq rt of 0.36 = q = 0.6 Since p + q = 1 à p must be 0.4 So p 2 = 0.16 = frequency of red eye color 16% of 1000 = 160 = # of homozygous red eye color 49

50 II. Hardy-Weinberg Principle 3. H-W Equa%on: Warnings You must understand the difference between frequency, percent, and individual You must understand the difference between heterozygous, homozygous dominant, and homozygous recessive You must understand the difference between allele frequency and the genotype frequency i.e. The allele frequency of A vs the homozygous dominant frequency 50

51 II. Hardy-Weinberg Principle 3. H-W Equa%on a. Type b. Example We can assume the locus that causes phenylketonuria (PKU) is in Hardy-Weinberg equilibrium given that: The PKU gene muta%on rate is low Mate selec%on is random with respect to whether or not an individual is a carrier for the PKU allele Natural selec%on can only act on rare homozygous individuals who do not follow dietary restric%ons The popula%on is large Migra%on has no effect as many other popula%ons have similar allele frequencies 51

52 II. Hardy-Weinberg Principle 3. H-W Equa%on b. Example The occurrence of PKU is 1 per 10,000 births. What is the frequency of carriers in the popula%on? q 2 = q = 0.01 The frequency of normal alleles is p = 1 q = = 0.99 The frequency of heterozygotes / carriers is 2pq = 2 x 0.99 x 0.01 = or approximately 2% of the U.S. popula%on. 52