Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Genes Within Populations Chapter 20 1 • “Through time, species accumulate differences; as a result, descendants differ from their ancestors. In this way, new species arise from existing ones.” – Charles Darwin 2 Evolutionary Theories • Jean-Baptiste Lamarck – “inheritance of acquired characteristics” Evolutionary Theories • Charles Darwin – “Descent with modification” Evolution Review • Progress of evolution: Gene Mutation Trait Natural selection Microevolution. 5 Genetic Variation and Evolution • Genetic variation: – “Differences in alleles of genes found within individuals in a population” – Raw material for natural selection if it meets three criteria. – Evolution results in a change in the genetic composition of a population. 6 • Natural selection and evolution are not the same • Evolution driven by natural selection creates populations that are better adapted to their environment 7 Fitness and its measurement • Fitness • Fitness has many components – Survival – Sexual selection – some individuals more successful at attracting mates – Number of offspring per mating 8 4 agents of evolutionary change 9 10 Selection vs Other Processes • Natural selection can be altered by other processes: –Mutation –Gene flow –Genetic drift 11 Founder effect Bottleneck effect 12 Case Studies Cheetah Bearded Vulture 13 Selection • Many traits affected by more than one gene • There are 3 types of multiple gene selection – Disruptive - “it pays to be very different” – Directional – “there can be only one” – Stabilizing - “it pays to be average” 14 Diversifying (Disruptive) Natural Selection African Black-billed seedcracker finches 15 Directional Natural Selection 16 Stabilizing Natural Selection 17 Limits of selection • Selection is the most powerful of all the forces behind genetic change. But there are limits to what it can accomplish. • Lack of genetic variation • Pleiotrophy - Multiple phenotypic effects of alleles • Epistasis 18 Gene Pools and Allele Frequencies • Gene pool – “all the alleles for all the DNA loci (locations) for all the individuals in a population”. • Each allele has its own frequency in a population. That frequency can be calculated. • If you know the frequency of an allele you can determine how often the trait it controls appears in a population and its ‘place’ in natural selection. 19 Hardy–Weinberg principle • Hardy–Weinberg equilibrium – “Genotypes frequencies do not change in a population if: 1. No mutation takes place 2. No genes are transferred to or from other sources 3. Mates are chosen randomly 4. The population size is very large 5. No natural selection occurs”. 20 Hardy – Weinberg Calculations • For 2 alleles (p and q) p2 + 2pq + q2 = 1 p2 = homozgous dominant (BB) pq = heterozygous dominant (Bb) q2 = homozygous recessive (bb) 21 Hardy – Weinberg Calculations 22 Allelic Frequency vs. Genotypic Frequency 1. No spots is a recessive trait in toads. The frequency of the recessive allele is 10%. What is q for this population? (Allelic frequency) 2. A population shows that 16% have the recessive trait of no spots. What is q for this population? (Genotypic frequency) 23 Practice In a certain population of 1000 fruit flies, 640 have red eyes while the remainder have sepia eyes. The sepia eye trait is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color? 24 Extra help • Go to YouTube • Type in Bozeman Biology Hardy Weinberg 25