1. © 2014 Pearson Education, Inc. Objective 5: TSWBAT recognize that genetic variation makes evolution possible.

2. © 2014 Pearson Education, Inc. Overview: The Smallest Unit of Evolution  One common misconception is that organisms evolve during their lifetimes  Natural selection acts on individuals, but only populations evolve  Consider, for example, a population of medium ground finches on Daphne Major Island  During a drought, large-beaked birds were more likely to crack large seeds and survive  The finch population evolved by natural selection

3. © 2014 Pearson Education, Inc.  Microevolution is a change in allele frequencies in a population over generations  Three mechanisms cause allele frequency change  Natural selection  Genetic drift  Gene flow  Only natural selection causes adaptive evolution

4. © 2014 Pearson Education, Inc.  Variation in heritable traits is a prerequisite for evolution  Mendel’s work on pea plants provided evidence of discrete heritable units (genes) Concept 21.1: Genetic variation makes evolution possible

5. © 2014 Pearson Education, Inc. Genetic Variation  Phenotypic variation often reflects genetic variation  Genetic variation among individuals is caused by differences in genes or other DNA sequences  Some phenotypic differences are due to differences in a single gene and can be classified on an “either- or” basis  Other phenotypic differences are due to the influence of many genes and vary in gradations along a continuum

6. © 2014 Pearson Education, Inc. Figure 21.3

7. © 2014 Pearson Education, Inc.  Genetic variation can be measured at the whole gene level as gene variability  Gene variability can be quantified as the average percent of loci that are heterozygous

8. © 2014 Pearson Education, Inc.  Genetic variation can be measured at the molecular level of DNA as nucleotide variability  Nucleotide variation rarely results in phenotypic variation  Most differences occur in noncoding regions (introns)  Variations that occur in coding regions (exons) rarely change the amino acid sequence of the encoded protein

9. © 2014 Pearson Education, Inc. Figure 21.4 1,000 Substitution resulting in translation of different amino acid Base-pair substitutions Insertion sites Deletion Exon Intron 1 500 2,5002,0001,500

10. © 2014 Pearson Education, Inc.  Phenotype is the product of inherited genotype and environmental influences  Natural selection can only act on phenotypic variation that has a genetic component

11. © 2014 Pearson Education, Inc. Figure 21.5a (a) Caterpillars raised on a diet of oak flowers

12. © 2014 Pearson Education, Inc. Figure 21.5b (b) Caterpillars raised on a diet of oak leaves

13. © 2014 Pearson Education, Inc. Sources of Genetic Variation  New genes and alleles can arise by mutation or gene duplication

14. © 2014 Pearson Education, Inc. Formation of New Alleles  A mutation is a change in the nucleotide sequence of DNA  Only mutations in cells that produce gametes can be passed to offspring  A “point mutation” is a change in one base in a gene

15. © 2014 Pearson Education, Inc.  The effects of point mutations can vary  Mutations in noncoding regions of DNA are often harmless  Mutations to genes can be neutral because of redundancy in the genetic code  Mutations that alter the phenotype are often harmful  Mutations that result in a change in protein production can sometimes be beneficial

16. © 2014 Pearson Education, Inc. Altering Gene Number or Position  Chromosomal mutations that delete, disrupt, or rearrange many loci are typically harmful  Duplication of small pieces of DNA increases genome size and is usually less harmful  Duplicated genes can take on new functions by further mutation  An ancestral odor-detecting gene has been duplicated many times: Humans have 350 functional copies of the gene; mice have 1,000

17. © 2014 Pearson Education, Inc. Rapid Reproduction  Mutation rates are low in animals and plants  The average is about one mutation in every 100,000 genes per generation  Mutation rates are often lower in prokaryotes and higher in viruses  Short generation times allow mutations to accumulate rapidly in prokaryotes and viruses

18. © 2014 Pearson Education, Inc. Sexual Reproduction  In organisms that reproduce sexually, most genetic variation results from recombination of alleles  Sexual reproduction can shuffle existing alleles into new combinations through three mechanisms: crossing over, independent assortment, and fertilization

19. © 2014 Pearson Education, Inc. Objective 6 TSWBAT describe the basic principles of population genetics including us of the Hardy-Weinberg theorem and equation.

20. © 2014 Pearson Education, Inc. Concept 21.2: The Hardy-Weinberg equation can be used to test whether a population is evolving  The first step in testing whether evolution is occurring in a population is to clarify what we mean by a population

21. © 2014 Pearson Education, Inc. Gene Pools and Allele Frequencies  A population is a localized group of individuals capable of interbreeding and producing fertile offspring  A gene pool consists of all the alleles for all loci in a population  An allele for a particular locus is fixed if all individuals in a population are homozygous for the same allele

22. © 2014 Pearson Education, Inc. Figure 21.6 Porcupine herd Beaufort Sea Fortymile herd Porcupine herd range Fortymile herd range MAP AREA ALASKA CANADA NORTHWEST TERRITORIES YUKON ALASKA

23. © 2014 Pearson Education, Inc. Figure 21.6a Porcupine herd

24. © 2014 Pearson Education, Inc. Figure 21.6b Fortymile herd

25. © 2014 Pearson Education, Inc.  The frequency of an allele in a population can be calculated  For diploid organisms, the total number of alleles at a locus is the total number of individuals times 2  The total number of dominant alleles at a locus is 2 alleles for each homozygous dominant individual plus 1 allele for each heterozygous individual; the same logic applies for recessive alleles

26. © 2014 Pearson Education, Inc.  By convention, if there are 2 alleles at a locus, p and q are used to represent their frequencies  The frequency of all alleles in a population will add up to 1  For example, p  q  1

27. © 2014 Pearson Education, Inc. Figure 21.UN01 CRCRCRCR CRCWCRCW CWCWCWCW

28. © 2014 Pearson Education, Inc.  For example, consider a population of wildflowers that is incompletely dominant for color  320 red flowers (C R C R )  160 pink flowers (C R C W )  20 white flowers (C W C W )  Calculate the number of copies of each allele  C R  (320  2)  160  800  C W  (20  2)  160  200

29. © 2014 Pearson Education, Inc.  To calculate the frequency of each allele  p  freq C R  800 / (800  200)  0.8 (80%)  q  1  p  0.2 (20%)  The sum of alleles is always 1  0.8  0.2  1

30. © 2014 Pearson Education, Inc. The Hardy-Weinberg Principle  The Hardy-Weinberg principle describes a population that is not evolving  If a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is evolving

31. © 2014 Pearson Education, Inc.  The Hardy-Weinberg principle states that frequencies of alleles and genotypes in a population remain constant from generation to generation  In a given population where gametes contribute to the next generation randomly, allele frequencies will not change  Mendelian inheritance preserves genetic variation in a population Hardy-Weinberg Equilibrium

32. © 2014 Pearson Education, Inc.  Hardy-Weinberg equilibrium describes the constant frequency of alleles in such a gene pool  Consider, for example, the same population of 500 wildflowers and 1,000 alleles where  p  freq C R  0.8  q  freq C W  0.2

33. © 2014 Pearson Education, Inc. Figure 21.7 Frequencies of alleles Gametes produced p  frequency of C R allele q  frequency of C W allele Alleles in the population Each egg: Each sperm:  0.8  0.2 80% chance 80% chance 20% chance 20% chance

34. © 2014 Pearson Education, Inc.  The frequency of genotypes can be calculated  C R C R  p 2  (0.8) 2  0.64  C R C W  2pq  2(0.8)(0.2)  0.32  C W C W  q 2  (0.2) 2  0.04  The frequency of genotypes can be confirmed using a Punnett square

35. © 2014 Pearson Education, Inc. Figure 21.8 Sperm Eggs 80% C R (p  0.8) 20% C W (q  0.2) p  0.8q  0.2 CRCR CRCR CWCW CWCW p  0.8 q  0.2 0.64 (p 2 ) C R 0.16 (pq) C R C W 0.16 (qp) C R C W 0.04 (q 2 ) C W Gametes of this generation: 64% C R C R, 32% C R C W, and 4% C W C W 64% C R (from C R C R plants) 16% C R (from C R C W plants) 4% C W (from C W C W plants) 16% C W (from C R C W plants) 80% C R  0.8  p 20% C W  0.2  q     64% C R C R, 32% C R C W, and 4% C W C W plants With random mating, these gametes will result in the same mix of genotypes in the next generation:

36. © 2014 Pearson Education, Inc. Figure 21.8a Sperm Eggs 80% C R (p  0.8) 20% C W (q  0.2) p  0.8 q  0.2 CRCR CRCR CWCW CWCW p  0.8 q  0.2 0.64 (p 2 ) C R 0.16 (pq) C R C W 0.16 (qp) C R C W 0.04 (q 2 ) C W

37. © 2014 Pearson Education, Inc. Figure 21.8b Gametes of this generation: 64% C R C R, 32% C R C W, and 4% C W C W 64% C R (from C R C R plants) 16% C R (from C R C W plants) 4% C W (from C W C W plants) 16% C W (from C R C W plants) 80% C R  0.8  p 20% C W  0.2  q     64% C R C R, 32% C R C W, and 4% C W C W plants With random mating, these gametes will result in the same mix of genotypes in the next generation:

38. © 2014 Pearson Education, Inc.  If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then  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

39. © 2014 Pearson Education, Inc. Figure 21.UN02

40. © 2014 Pearson Education, Inc. Conditions for Hardy-Weinberg Equilibrium  The Hardy-Weinberg theorem describes a hypothetical population that is not evolving  In real populations, allele and genotype frequencies do change over time

41. © 2014 Pearson Education, Inc.  The five conditions for nonevolving populations are rarely met in nature 1.No mutations 2.Random mating 3.No natural selection 4.Extremely large population size 5.No gene flow

42. © 2014 Pearson Education, Inc.  Natural populations can evolve at some loci while being in Hardy-Weinberg equilibrium at other loci  Some populations evolve slowly enough that evolution cannot be detected

43. © 2014 Pearson Education, Inc. Applying the Hardy-Weinberg Principle  We can assume the locus that causes phenylketonuria (PKU) is in Hardy-Weinberg equilibrium given that 1.The PKU gene mutation rate is low 2.Mate selection is random with respect to whether or not an individual is a carrier for the PKU allele

44. © 2014 Pearson Education, Inc. 3.Natural selection can only act on rare homozygous individuals who do not follow dietary restrictions 4.The population is large 5.Migration has no effect, as many other populations have similar allele frequencies

45. © 2014 Pearson Education, Inc.  The occurrence of PKU is 1 per 10,000 births  q 2  0.0001  q  0.01  The frequency of normal alleles is  p  1 – q  1 – 0.01  0.99  The frequency of carriers is  2pq  2  0.99  0.01  0.0198  or approximately 2% of the U.S. population