Constant Allele Frequencies

1. Constant Allele Frequencies Hardy-Weinberg Equilibrium

2. Population • An interbreeding group of the same species within a given geographical area • Gene pool • the collection of all alleles in the members of the population • Population genetics • the study of the genetics of a population and how the alleles vary with time • Gene Flow • alleles can move between populations when individuals migrate and mate

3. Allele Frequencies Allelic # of particular allele Frequencytotal # of alleles in the population • Count both chromosomes of each individual • Allele frequencies affect the genotype frequencies • The frequency of each type of homozygote and heterozygote in the population

4. Phenotype Frequencies • Frequency of a trait varies in different populations Table 14.1

5. Microevolution and Macroevolution • Microevolution • Genetic change due to changing allelic frequencies in populations • Macroevolution • The formation of new species

6. Allelic frequencies can change when there is: • Nonrandom mating • Individuals of one genotype are more likely to produce offspring with each other than with those of other genotypes • Gene flow • e.g. migration • Genetic drift • Reproductively isolated groups form within or separate from a larger population • Mutation • Introduces new alleles into the population • Natural selection • Individuals with a particular genotype are more likely to produce viable offspring

7. Hardy-Weinberg Equilibrium • Developed by mathematicians • A condition in which allele frequencies remain constant • Used algebra to explain how allele frequencies predicts genotype and phenotype frequencies in equilibrium

8. Hardy-Weinberg Equilibrium p + q = 1 All of the allele frequencies together equals 1 or the whole collection of alleles p = allele frequency of one allele (e.g. dominant) q = allele frequency of a second allele (e.g. recessive) p2 + 2pq + q2 = 1 All of the genotype frequencies together equals 1 p2 and q2 =genotype frequencies for each homozygote 2pq = genotype frequency for heterozygotes 2 possible combinations (p egg + q sperm or vice versa)

9. Figure 14.3

11. Table 14.2

12. Applying Hardy-Weinberg Equilibrium • Used to determine carrier probability • Homozygous recessive used to determine frequency of allele in population (phenotype is genotype)

13. Applying Hardy-Weinberg Equilibrium: Cystic Fibrosis

14. Calculating Carrier Frequency for X-linked Traits Figure 14.6

15. DNA Profiling (a.k.a. DNA Fingerprinting • Hardy-Weinberg equilibrium applies to portions of the genome that do not affect phenotype • They are not subject to natural selection • Short repeated segments that are not protein encoding, distributed all over the genome • Detects differences in repeat copy number • Calculates probability that certain combinations can occur in two sources of DNA • Requires molecular techniques and population studies

16. Preparing DNA for Profiling –Restriction Enzymes • Chop up the DNA at specific sequences using “restriction enzymes” • Creates RFLPs • Restriction fragment length polymorphisms

17. Preparing DNA for Profiling –Running a Gel • Run samples on an agarose or polyacrylamide gel • DNA has a negative charge so it will travel toward a positive charge • Larger fragments will not move as far through the gel

18. DNA Profiling • Developed in 1980s • Identifies individuals • Used in forensics, agriculture, paternity testing, and historical investigations • DNA can be obtained from many sources

19. DNA Profiles Figure 14.9

20. DNA Profiling • Types of repeats • Variable number tandem repeats (VNTRs) • Short tandem repeats (STRs) • Shorter than VNTRs • Useful if DNA from sample is fragmented or degraded • mtDNA • Useful if nuclear DNA is highly damaged

21. A Sneeze Identifies Art Thief Table 14.6

22. Comparing DNA Sequences Figure 14.10 Figure 14.10