Genetics

1. Genetics Explain the basic rules and processes associated with the transmission of genetic characteristics

2. Describe the evidence for dominance, segregation and the independent assortment of genes on different chromosomes, as investigated by Mendel

3. Introduction • Heredity • is the passing of traits from parents to offspring • Genetics • is the study of the patterns of inheritance as hereditary characteristics or traits • Gregor Mendel • the "father of modern genetics“ • an Austrian monk • published his completely new and thoroughly documented ideas of inheritance in 1866

4. Introduction • His model was so simple that scientists who read it at that time considered it "trivial“ • it received little attention and no recognition until it was rediscovered in 1900 after his death (simultaneously by 3 different people) • In the meantime, • chromosomes had been named • their movements during mitosis and meiosis observed and described

5. Introduction • 1902 • scientists realized that chromosomes moved precisely as reported by Mendel • Once the connection between chromosomes and heredity was established, the science of genetics was reborn • Mendel was the first person to realize that genetic traits are inherited as separate particles

6. Introduction • He did not actually see these particles • but he predicted their existence based on patterns of inheritance • He proposed that organisms have a pair of "factors" for each trait • one from each parent • We NOW know that the particles of inheritance are segments of DNA • which we call genes

7. Mendel's Experiments • Mendel worked with garden peas • available in many different varieties • E.g. pure breeding tall, pure breeding dwarf • Pea flowers contain both male and female parts and normally self-pollinate • but can easily be artificially cross-pollinated with other pea plants • Mendel crossed plants of two varieties with contrasting traits (such as tall and dwarf) to see what would happen.

8. Mendel's Experiments • Mendel worked with seven traits, each which occurred in two distinct forms • Mendel began by studying crosses involving only one trait at a time • Example: Flower color • P1: (parental generation) • pure-breeding red flowered plants X pure-breeding white flowered plants • F1: (first filial generation) • red-flowered hybrids (genetically mixed offspring) • F2: (second filial generation) • 3/4 red-flowered and 1/4 white-flowered

9. Mendel's Laws • Inherited characteristics are controlled by pairs of factors • genes • one from each parent. • One gene may “mask” the effect of another. • The gene which is expressed is dominant, while the one which is masked is recessive. • Pairs of genes segregate during gamete formation • so each sex cell contains only one member of a pair of genes.

10. Terms • Alleles • Two or more alternate forms of a gene, which produce contrasting effects for a certain trait • e.g. red (R) and white (r) for flower colour of peas • Homozygous • having two of the same allele • eg. red/red (RR) • purebred • Heterozygous • having two different alleles eg. red/white (Rr)

11. Terms • Genotype • the genetic makeup of an individual • Phenotype • the expression of the genes, or appearance of an individual • Purebred • an organism having all homozygous gene pairs • Hybrid • an organism having at least one heterozygous gene pair

12. Terms • Monohybrid • an organism having only oneheterozygous gene pair • Dihybrid • an organism having two heterozygous gene pairs

13. Monohybrid Cross Purebred Red Purebred White Phenotypes RR x rr Genotypes Rr Rr Rr Rr F1 Genotypes

14. Gametes !! Gametes !! Monohybrid Punnet Square Genotype of Parent #2 Male Female R R r Rr Rr Genotype of Parent #1 r Rr Rr

15. Monohybrid Cross Purebred Red Purebred White Phenotypes RR x rr Genotypes Rr Rr Rr Rr F1 Genotypes Rr x Rr F1 Self Pollenate RR Rr rR F2 Genotypes rr

16. Monohybrid Cross Purebred Red Purebred White Phenotypes RR x rr Genotypes Rr Rr Rr Rr F1 Genotypes Rr x Rr F1 Self Pollenate RR Rr Rr F2 Genotypes rr

17. Monohybrid Cross • The phenotypic ratio for a monohybrid cross is always 3:1 • dominant trait : recessive trait

18. Predicting the Outcome of a Genetic Cross • When we know the genotypes of parents used in a genetic cross, we can predict the genotypes of the offspring and their expected ratios • Must use a Punnett square is used • named after some guy named Punnett • A geneticist • Basically it’s a just a fancy chart

19. Gametes !! Gametes !! Monohybrid Punnet Square Genotype of Parent #2 Male Female R R r Rr Rr Genotype of Parent #1 r Rr Rr

20. Practice

21. If an organism has the dominant phenotype, how can you determine whether it is homozygous or heterozygous?

22. Test Cross • You conduct a test cross. • Mate it with an organism of a known genotype and see what you get. • The only known genotype that is observable is HOMOZYGOUS RECESSIVE (rr) • For example: • determine whether a red-flowered pea plant is homozygous or heterozygous

23. Test Cross P: Red flowered X White-flowered   R? rr F1: Suppose the cross produces allred flowers Rr Rr Rr Rr • If no offspring showing the recessive phenotype are produced, the unknown parent must be … • homozygous

24. Purebred Red Purebred White Phenotypes RR x rr Genotypes Rr Rr Rr Rr F1 Genotypes

25. Test Cross P: Red flowered X White-flowered   R? rr F1: Suppose the cross produces 50%red flowers and 50% white flowers • The only way a white flower could appear is if it received a recessive allele from the unknown parent. • The unknown parent must be … • HETEROZYGOUS

26. Rr x rr P1 Rr Rr F1 Genotypes rr rr

27. Dihybrid Cross • In addition to his monohybrid crosses, Mendel performed dihybrid crosses of plants with two different pairs of contrasting alleles • In one experiment, Mendel crossed plants homozygous for seeds that were both round and yellow with plants homozygous for wrinkled, green seeds

28. Dihybrid Cross • All the F1 offspring had round, yellow seeds • Self-fertilization of the F1 plants produced and F2 generation of seeds with the following phenotypes: 315 round yellow 108 round green 101 wrinkledyellow 32 wrinkledgreen

29. Dihybrid Cross • To find the ratio among the F2 phenotypes, • we take the number of offspring in the smallest category - 32 - and divide it into the number of offspring in the other categories: • then the quotient is rounded to the nearest whole number

30. Dihybrid Cross • Thus Mendel determined the phenotypic ratio in the F2 generation to be 9:3:3:1 • This is the ratio typical of a dihybrid cross in which both pairs of alleles show a dominant-recessive relationship

31. Dihybrid Cross • Mendel explained these data by assuming that the genes governing seed color and seed shape move independently during gamete formation • In the process of independent assortment, each pair of alleles behaves as it would in a monohybrid cross - independently of the other pair  • A dihybrid can produce four possible gene combinations (with equal probability) • If the alleles are: R = round r = wrinkled Y = yellow y = green • The possible gamete combinations are RY Ry rY ry

32. Dihybrid Cross Parent: P Gametes: F1: F1 Gametes: F2: RRYY x rryy  RY ry RrYy  RY, Ry, rY, ry 9/16 round, yellow (R_Y_) 3/16 round, green (R_yy) 3/16 wrinkled, yellow (rrY_) 1/16 wrinkled, green (rryy)

35. Practice

36. Multiple Alleles& Incomplete Dominance

37. Compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incomplete dominant, and codominant alleles • Explain the relationship between variability and the number of genes controlling a trait

38. Multiple Alleles • The genes which we have studied so far have only two different alleles: • Many genes actually exist in more than two allelic forms, • Although only two genes control coat colour in rabbits it is controlled by a series of four alleles for the same gene: • C Full colour • Cch Chinchilla • ch Himalayan • c Albino

39. Multiple Alleles • C + any of the 4 • Cch+ anything but C • chch, chc • c c • The dominance hierarchy of these alleles is C > Cch > ch > c • Determine the genotypes for the following phenotypes: PhenotypePossible Genotype • Full color • Chinchilla • Himalayan • Albino

40. Incomplete Dominance • In some cases, a heterozygous organism shows a blending of genes because neither gene is dominant: • this is termed incomplete dominance • for example, in snapdragons, neither the red nor the white allele is dominant…

41. Incomplete Dominance Parent: F1: F2: Red Flowers x White Flowers Pink Flowers ¼ Red flowers ½ Pink flowers ¼ White flowers RR x rr Rr, Rr, Rr, Rr RR Rr rr

42. Codominance • If two different alleles each contribute to a phenotype, they are termed codominant • One of the best-known example of codominant genes occurs in humans, and determine ABO blood types • There are three possible alleles: • IA • IB • i

43. CodominanceBlood Type Phenotype Possible Genotypes A IA IA, IA i B IB IB, IB i AB IA IB O i i

48. Practice

49. Chromosome Mapping • Explain the influence of gene linkage and crossing over on variability

50. Chromosome Mapping Chromosomal Theory of Inheritance • Genes are located on chromosomes • Chromosomes undergo segregation during meiosis • Chromosomes assort independently during meiosis • Each chromosome contains many different genes