Population Dynamics

1. Population Dynamics Humans, Sickle-cell Disease, and Malaria How does a population of humans become resistant to malaria?

2. Natural Selection • Overproduction • Environmental pressure/competition • Pre-existing individual variation • Heritable traits • Happens over generations (time) • Happens in populations (not single individuals) • Offspring must be viable and fertile

3. The Origins of Genetic Variation • Offspring of sexual reproduction are genetically different from their parents and from one another. • Meiosis • Random mutations • Crossing over • Independent assortment of chromosomes • Random fertilization

4. Meiosis and comparing it to Mitosis

5. The Origins of Genetic Variation • Offspring of sexual reproduction are genetically different from their parents and from one another. • Meiosis • Random mutations • Crossing over • Independent assortment of chromosomes • Random fertilization

6. Intergenerational Mutation Rate • By how many mutations does your genome differ from your parents genome? • Roach, et al., Science (2010) found about 60 mutations, 30 from each parent, that occurred during meiosis. Hemophilia in the Royal Family: Hypothesis - hemophilia allele arose through mutation in gamete of Queen Victoria’s mother or father.

7. Crossing Over • In crossing over, • Homologous chromosomes exchange genetic information. • Genetic recombination occurs.

8. Independent Assortment of Chromosomes • In independent assortment, every chromosome pair orients independently of the others during meiosis.

9. Random Fertilization • The human egg cell is fertilized randomly by one sperm, leading to genetic variety in the zygote.

10. Natural Selection • Overproduction • Environmental pressure/competition • Pre-existing individual variation • Heritable traits • Happens over generations (time) • Happens in populations (not single individuals) • Offspring must be viable and fertile

11. Heritable Variation and Patterns of Inheritance - Ch 9 • Gregor Mendel • Was the first person to analyze patterns of inheritance. • Deduced the fundamental principles of genetics.

12. Figure 9.6a

13. Monohybrid Crosses • A monohybrid cross is a cross between parent plants that differ in only one characteristic.

14. Mendel developed four hypotheses from the monohybrid cross: • There are alternative forms of genes, called alleles. • For each characteristic, an organism inherits two alleles, one from each parent. • Alleles can be dominant or recessive. • Gametes carry only one allele for each inherited characteristic.

15. Mendel developed four hypotheses from the monohybrid cross: • There are alternative forms of genes, called alleles. • For each characteristic, an organism inherits two alleles, one from each parent. • Alleles can be dominant or recessive. • Gametes carry only one allele for each inherited characteristic.

16. Mendel developed four hypotheses from the monohybrid cross: • There are alternative forms of genes, called alleles. • For each characteristic, an organism inherits two alleles, one from each parent. • Alleles can be dominant or recessive. • Gametes carry only one allele for each inherited characteristic.

17. Mendel developed four hypotheses from the monohybrid cross: • There are alternative forms of genes, called alleles. • For each characteristic, an organism inherits two alleles, one from each parent. • Alleles can be dominant or recessive. • Gametes carry only one allele for each inherited characteristic.

19. Mendel developed four hypotheses from the monohybrid cross: • There are alternative forms of genes, called alleles. • For each characteristic, an organism inherits two alleles, one from each parent. • Alleles can be dominant or recessive. • Gametes carry only one allele for each inherited characteristic.

20. Phenotype • An organism’s physical traits; what it looks like. • Genotype • An organism’s genetic makeup; what genes it has.

21. Genetic Alleles and Homologous Chromosomes Figure 9.7

22. Independent Assortment of Chromosomes • In independent assortment, every chromosome pair orients independently of the others during meiosis.

23. Figure 9.5

24. Dihybrid cross Is the mating of parental varieties differing in two characteristics.

25. Mendel’s law of independent assortment states that • Each pair of alleles segregates independently of the other pairs during gamete formation.

26. Figure 9.23

27. Using a Testcross to Determine an Unknown Genotype • A testcross is a mating between • An individual of unknown genotype and a homozygous recessive individual.

28. Family Pedigrees • Shows the history of a trait in a family. • Allows geneticists to analyze human traits.

29. Human Disorders Controlled by a Single Gene

30. Variations On Mendel’s Laws • Some patterns of genetic inheritance are not explained by Mendel’s laws. • Incomplete dominance • Codominance • Pleiotropy • Polygenic Inheritance

31. Incomplete Dominance in Plants • In incomplete dominance, F1 hybrids have an appearance in between the phenotypes of the two parents.

32. Incomplete Dominance in People • In incomplete dominance, F1 hybrids have an appearance in between the phenotypes of the two parents.

33. ABO Blood Type: An Example of Multiple Alleles and Codominance • The ABO blood groups in humans are an example of multiple alleles.

34. The immune system produces blood proteins • That may cause clotting when blood cells of a different type enter the body.

35. Pleiotropy and Sickle-Cell Disease • Pleiotropy is the impact of a single gene on more than one characteristic. • Sickle-cell disease is an example.

36. Polygenic Inheritance • Polygenic inheritance is the additive effects of two or more genes on a single phenotype.

37. The Role of Environment • Many human characteristics result from a combination of heredity and environment.

38. The Chromosomal Basis of Inheritance • The chromosome theory of inheritance states that • Genes are located at specific positions on chromosomes. • The behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns.

39. Figure 9.23

40. Linked Genes • Linked genes • Are located close together on a chromosome. • May be inherited together.

41. The Process of Science: Are Some Genes Linked? • Using the fruit fly Drosophila melanogaster, Thomas Hunt Morgan determined • That some genes were linked based on the inheritance patterns of their traits.

42. What to expect if the genes follow the rules of independent assortment GL gl gL Gl gl GgLl ggll ggLl Ggll 50% recombinant phenotypes 50% parental phenotypes

43. Unexpected Results!! Figure 9.24

44. Linked Genes The “P”, “a”, and “b” genes are linked because they are on the same chromosome.

45. What to expect if the genes are linked. GL gl gl GgLl ggll 100% parental phenotypes Figure 9.24

46. Unexpected Results!! Figure 9.24

47. Genetic Recombination: Crossing Over • Two linked genes • Can give rise to four different gamete genotypes because of crossing over!

48. Figure 9.25

49. Figure 9.26

50. Linkage Maps • Studies using Drosophila • Developed a method for mapping gene loci. • Resulted in linkage maps.