Microevolution Ch. 20

1. MicroevolutionCh. 20

2. What Is Microevolution? • Evolution a change in a species genes over time • Time needed various between populations • Different populations can experience different changes • Microevolution change in the genes in one specific population • Easier to monitor • Can lead to speciation • Monitored through phenotypic variation (changes in appearance) and genotypic variation (changes in DNA sequence) • All changes must be inheritable for evolution to occur

3. Ways to Describe Variation • Quantitative variation one trait expressed in a range; ex. Height, weight, size, etc… • Average of population fits in the middle of the extremes (bell curve) • Qualitative variation one trait expressed in only a set number of ways; blood type, flower color, etc… • No intermediates (mixing of traits) • Polymorphism • Phenotype ≠ Genotype • 50% A type blood doesn’t mean 50% iAiA

4. Sources of Genetic Variation • New phenotypes do not mean a change in the populations genome • Phenotypic changes can be caused by the environment • Artic Hare white color in cold temperatures • New alleles mutations or new DNA from new members • Rearrange old alleles 3 methods of variation from meiosis; 10600 combinations of human DNA

5. Population Genetics • Gene Pool total genome in a population • Genotype frequencies percent genes occur in population • Three types (AA, Aa, aa) • Allele frequencies percent alleles occur in population • Two types (A or a) • AA, Aa, aa 50% A and 50% a • p= % of A • q= % of a

6. Hardy-Weinberg Equation • p2 + 2pq + q2 = 1p + q = 1 • p2 AA • 2pq Aa • q2 aa • What is the frequency of heterozygotes if the dominate phenotypes occur at 19%? • Dominate phenotypes = p2 + 2pq = 0.19 • q2= 1- 0.19 = 0.81 q = 0.9 • p + q = 1 p = 1-0.9 = 0.1 • 2pq = 2(0.1)(0.9)= 0.18

7. Hardy-Weinberg Equation • A plant species ability to grow in nickel contaminated soil is determined by a dominate allele • If 60% of the plant seeds grow in the soil, what is the frequency of this resistant allele? • Of the plants that grow, what percent are heterozygous? i) p2+2pq= 0.6 ; q2= 1-0.6 = 0.4; q= 0.63 1-q = p = 1-0.63= 0.37 ii) p2 + 2pq= 0.6; p=0.37 p2 = (0.37)2 = 0.14 2pq = 0.6 – 0.14= 0.46

8. The Null Hypothesis • What must you always have in a controlled experiment? • A control group • How can we compare a group of flowers in the wild to a control group? There is no control group in nature • Null Models predicts outcomes if no factors of effected genetic variation • Hardy and Weinberg designed the conditions that must ALL occur for genetic equilibrium to occur • Hardy-Weinberg Principle

9. Hardy-Weinberg Principle • ALL of the following must occur for a population not to change: • No mutations • No migration • Infinite in size • All genotypes will survive and reproduce • All members mate randomly • No population, even a controlled one, will ever have all of these traits • Example of a perfect control group in genetics

10. Causes of Microevolution • Mutation direct change in the genome by altering the DNA sequence • Deleterious mutations that produce harmful effects • Lethal cause the organism to die before reproducing; often die in early development • Neutral neither helpful nor harmful • Advantageous positive effect; might be promoted in future generations • Mutations in somatic cells do not effect evolution. Why? • Only mutations in gametes get passed on

11. Causes of Microevolution 2) Gene Flow immigration of new alleles into the population through new members • Must reproduce with old members to introduce new alleles • If the new members are very similar to the old population there may be little effect • Very different new members can cause a huge shift

12. Causes of Microevolution 3) Genetic Drift random events the remove members from the population • genes do not effect survival • Small populations are greatly effected; large populations experience little effect • Population Bottleneck: • Major disaster removes a large part of the population, those left are the only source of variation • Founder Effect: • Members that start a new population in a new area are the only source of variation

13. Causes of Microevolution 4) Natural Selection benefited traits to a certain environment lead to the increased survival rate of that individual • Increase the appearance of those traits (relative fitness) • 3 types: • Directional one extreme of trait is favored • Stabilizing intermediate of extremes of the trait is favored; most common • Disruptive both extremes of trait are favored; least common

14. Causes of Microevolution 5) Sexual Selection males/females can be selected for mating based on traits • Intersexual males/females selected based on useless traits • Color patterns, mating songs, etc… • Intrasexual males/females use traits to compete for access to each other • Body size, tusks, etc… • Sexual Dimorphism males and females differ greatly in size • In both cases, if the trait is too extreme the individual will have limited survival • Too brightly colored= easy to find • Too big of antlers= too hard to move • Balance is best

15. Balancing Polymorphism • Recessive traits survive selection through carriers • Even negative mutation are conserved if the heterozygous form has an advantage • Sickle Cell Anemia: • HbSHbS normal blood; can get Malaria • HbAHbA sickle blood; can’t get Malaria • HbSHbA defective blood, but resistant to Malaria • Heterzygous is best in malaria ridden environments

16. Frequency-Dependent Selection • Advantage of a trait can change depending on how often it appears • Water Boatmen: • Insect species with different shades of brown • Darkest are easiest to see; least advantages • Dark drop and light becomes common, common are the focus of predator fish making darker advantages

17. Path of Adaptations • The cause for adaptations is not always clear • Current adaptive traits may have originated from environments very different from current ones • Traits may have had different uses when first forming • Bone structures in shoulders use by all birds for flight formed long before birds existed • Passed on from small dinosaurs and used by birds for flight

18. Homework • Suggested Homework: • Test Your Knowledge Ch. 20 • Actual Homework: • Discuss the Concepts #4 • Design the Experiment • Apply Evolutionary Thinking