Chapter 16: Evolution of Populations

HOMEWORK Chapter 16 Section Assessments: Due Fri. 5/2 Chapter 16.1 SA: p. 396 (1-5) Chapter 16.2 SA: p. 402 (1-5) Chapter 16.3 SA: p. 410 (1-2) Chapter 16 Assessment: p. 413 (1-10, 12, 17, 18, 19)

VOCABULARY (DUE FRI. 5/2) Provide the glossary definition and etymology for the following terms: Gene pool Hardy-Weinberg principle Relative Frequency Genetic equilibrium Single-gene trait Speciation Polygenic trait Reproductive isolation Directional selection Behavioral isolation Stabilizing selection Geographic isolation Disruptive selection Temporal isolation Genetic drift Founder effect

16.1: Genes and Variation A weakness in Darwin’s theory stemmed from his lack of understanding in genetic variation. In the 1930s, evolutionary biologists combined Mendel’s work with that of Darwin’s to support evolutionary change, specifically the process of natural selection. How do you think Mendel would have felt about that?

16.1 Variation and Gene Pools Population: a group of individuals of the same species that interbreed. Gene pool: consists of all genes, including all the different alleles, that are present in a population. Relative frequency: the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur. (Fig. 16-2) Key Concept: In genetic terms, evolution is any change in the relative frequency of alleles in a population.

16.1 Sources of Genetic Variation Key Concept: The two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction. Remember mutations are changes in the genetic code. Some are expressed, some remain silent. Some mutations can affect an organism’s fitness, while others have not effect. Crossing over and independent assortment during gamete formation leads to genetic variation. (23 pairs of chromosomes can have 8.4 million different combinations of genes!)

16.2 Evolution as Genetic Change

16.2 Natural Selection on Single-Gene Traits Key Concept: Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution. (Fig. 16-5) Remember: Evolution is change over time in the relative frequencies of alleles in a population, therefore it is populations that can evolve, not individual organisms.

16.2 Natural Selection on Polygenic Traits Key Concept: Natural selection can affect the distributions of phenotypes in any of three ways: Directional Selection: when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end. (Fig. 16-6) Stabilizing Selection: center curve has higher fitness (Fig. 16-7) Disruptive Selection: upper and lower ends have high fitness (Fig. 16-8)

Natural Selection and Normal Distribution One extreme favored Average favored Both extremes favored

16.2 Genetic Drift Key Concept: In small populations, individuals that carry a particular allele may leave more descendants that other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population. (Fig. 16-9) Genetic Drift: Random change in allele frequencies that occurs in small populations Founder Effect: A situation in which allele frequencies change as a result of the migration of a small subgroup of a population

16.2 Hardy-Weinberg and Genetic Equilibrium Genetic Equilibrium: A situation in which allele frequencies remain constant. Key Concept: Five conditions are required to maintain genetic equilibrium from generation to generation: Random mating Large population size No movement into or out of the population No mutations No natural selection

16.2 Hardy-Weinberg Equation (p. 401-402) p + q = 1 p = dominant allele frequency (A) q = recessive allele frequency (a) p2 + 2pq + q2 = 1 p2: frequency of AA homozygous 2pq: frequency of Aa heterozygous q2: frequency of aa homozygous 1: sum of frequencies for all genotypes (100%) Extra Credit Assignment!! Due Fri. 5/2

Bio Warm-Up April 28, 2014 (Do Not Copy) List and describe three types of natural selection that occur in a population. Draw a distribution curve for the population before and after selection. The inability to taste PTC paper (t) is recessive to being able to taste it (T). At UC Academy, 135 out of the 450 students are unable to taste PTC paper. Calculate the frequency for the following: homozygous dominant individuals heterozygous individuals homozygous recessive individuals frequencies of the T and t alleles in our school population.

Bio Warm-Up April 29, 2014 (Do Not Copy) Having mid-digital hair (hair on the skin of the second bone in your finger) is dominant to not having hair there. At Chaffey College, 7350 out of the 15,000 students have no mid-digital hair. Calculate the frequency of the following individuals who are: homozygous recessive heterozygous homozygous dominant dominant mid-digital hair allele (H) recessive no mid-digital hair allele (h). When individuals at only one end of a bell-shaped curve of phenotype frequencies have high fitness, the result is ___________ selection.

16.3 The Process of Speciation

16.3 Isolating Mechanisms Speciation: formation of new species Key Concept: As new species evolve, populations become reproductively isolated from each other. Reproductive Isolation: When members of two populations cannot interbreed and produce fertile offspring. They now have separate gene pools.

Is the definition of species constant? 16.3 Isolating Mechanisms Causes of reproductive isolation: Behavioral Isolation: capable of interbreeding, but have different courtship rituals or other reproductive behaviors. Geographic Isolation: separated by physical barriers (i.e. rivers, mountains, etc…) Temporal Isolation: reproduce at different times. Is the definition of species constant? “Can vs. Will”

16.3 Testing Natural Selection in Nature Peter and Rosemary Grant have spent more than 20 years observing collecting data on Galapagos finches. They found variation in physical characteristics. They observed natural selection occurring during drought seasons.

16.3 Speciation in Darwin’s Finches Key Concept: Speciation in the Galapagos finches occurred by founding of a new population, geographic isolation, changes in the new population’s gene pool, reproductive isolation, and ecological competition.

16.3 Studying Evolution Since Darwin Read: Unanswered Questions (p. 410) “New data from genetics, physics, and biochemistry could have proved him wrong on many counts. They didn’t.” “…while the Grants observed changes in the size of the finches’ beaks, they did not observe the formation of a new species.” Why is understanding evolution important?