Mendelian Genetics

1. Mendelian Genetics

2. Genetics: The Basics • Allele- An alternative form of a gene • Diploid organisms have one copy on each homologous chromosome • Represented by letters: • Capital letter = dominant form • Lower case letter = recessive form • Example= Eye Color • Controlled by 2 alleles • Blue Eyes = bb • Brown eyes= Bb or BB

3. Dominant allele-fully expressed in the organism's appearance Recessive allele-no noticeable effect on the organism's appearance

5. Genetics: The Basics • Heterozygous: Have 2 different forms of the allele • Example: • Brown Eyes = Bb = heterozygous • Homozygous: Have 2 of the same forms of the allele • Example: • Blue Eyes = bb = homozygous recessive • Brown Eyes = BB = homozygous dominant

6. Genetics: The Basics • Genotype = the genetic makeup of an organism • Example = BB, Bb, bb • Phenotype = the physical expression of genes • Example = • Brown Eyes = phenotype of either the BB or Bb genotype • Blue Eyes= phenotype of the bb genotype Remember that phenotype is not necessarily an appearance- It can be things like enzyme production, behavior, etc!! It is ANY expression of a gene!!

7. Gregor Mendel *1843 entered monastery *1851-53 studied at Univ. of Vienna *1857 started breeding garden peas * 1860 started forging data!!

8. MENDEL'S MAIN QUESTION Do units of inheritance retain integrity (preserved) or blend???? Sample Question: If you cross a purple flower with a white flower are these flower colors retained in future crosses or are they blended to form an intermediate color?

11. Law of Segregation-two alleles for a character are packaged into separate gametes 2 plants crossed Self-fertilized

13. Mendel's findings 1. Alternative version of genes (alleles) account for variations in inherited characters Homologous chromosomes Purple flowers White flowers

14. Mendel's findings 2. For each character, an organism inherits two alleles, one from each parent. maternal Homologous chromosomes paternal Purple flowers White flowers

15. Mendel's findings 3. If two alleles differ, the dominant allele is fully expressed in the organism's appearance. recessive dominant Purple flowers White flowers

16. Mendel's findings 4. The two alleles for each character segregate during gamete production. dominant recessive Seed shape PP pp Gametes P p

17. Punnett Square Predicts the results of a genetic cross between individuals with known genotypes

18. Rules for Genetic Problems 1. Identify traits (alleles) and assign letters to represent the various traits: capital letters for dominant traits; lower case letters for recessive traits. 2. Set up parental cross. 3. Draw individual gametes with corresponding letter for trait. 4. Identify F1 offspring phenotype and genotype. 5. Setup F1 cross. 6. Draw individual gametes with corresponding letter for trait. 7. Set up Punnett square to identify individual genotypes and phenotypes for F2 offspring.

19. EXAMPLE: SEED COLOR C c c C c dominant recessive CC cc c C C CC 3 Cc Cc cc 1

20. EXAMPLE: POD SHAPE S s s S s dominant recessive SS ss s S S SS 3 Ss Ss ss 1

21. Monohybrid Cross Follows single trait

22. Test Cross Breeding a homozygous recessive with a dominant phenotype (unknown genotype) can determine an unknown allele.

23. In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? F1 generation, test cross: Ss Ss What is the genotypic ratio? What is the phenotypic ratio?

24. The test cross To identify the genotype of yellow-seeded pea plants as either homozygous dominant (YY) or heterozygous (Yy), you could do a test cross with plants of genotype _______. A. y B. Y C. yy D. YY E. Yy

25. Predicting the results of a test cross A test cross is used to determine if the genotype of a plant with the dominant phenotype is homozygous or heterozygous. If the unknown is homozygous, all of the offspring of the test cross have the __________ phenotype. If the unknown is heterozygous, half of the offspring will have the __________ phenotype. A. dominant, recessive B. recessive, dominant

26. Question: How are two traits inherited? • DIHYBRID CROSS • Experimental Approach: A cross involving two true-breeding traits. • System: Pea Plants; seed color (Y/y) • and seed shape (S/s).

27. F1 Generation

28. F1 Generation

29. F1 Generation • Each of the male gametes types (SY, Sy, sY, sy) can fuse with each of the female gametes types (SY, Sy, sY, sy). • 16 possible combinations of gametes are possible. • We will see that there are 9 possible genotypes and 4 possible phenotypes. • 4. The two parental phenotypes, and • two new phenotypes were obtained.

30. Dihybrid Cross Follows two traits 9:3:3:1 RATIO

31. Dihybrid Cross

32. Law of Independent Assortment-separation of alleles into separate gametes

34. Inheritance that diverges from Mendel's inheritance GENE INTERACTIONS The relationship between the genotype and phenotype is rarely simple. * Each character is rarely controlled by one gene *Each gene usually has more than two alleles, with not always being dominant over the other

35. Incomplete Dominance Heterozygotes show a distinct intermediate phenotype, not seen in homozygotes Traits are separable in further crosses Not BLENDED

36. In CODOMINANCE, both alleles are expressed and functional, though they may be different. Most genes have more than two alleles in a population. (IA, IB, I)

37. Pleiotrophic Most genes affect more than one phenotypic character.

38. Pleiotropy:Albinism A single defect in one of the enzymes catalyzing tyrosine to melanin can affect multiple phenotypic characters, from eye color to skin color to hair color.

39. Epistasis A gene at one locus alters the phenotypic expression of a gene at a second locus. bb with dominant C allele results in brown mouse

40. Pedigree Analysis Information about presence/absence of phenotypic trait is collected from individuals in a family across generations.

41. Having the past help predict the future

43. Sex-linked traits • In humans, 2 of our 46 chromosomes are • classified as sex chromosomes • Females = XX • Carried on ova • Males = XY • Carried on sperm • In females, only 1 X chromosome is active • Sex linked traits usually aren’t expressed- • In males, their only X chromosome is active • No other X chromosome to block sex linked trait

44. Sex-linked traits In humans, the genes for colorblindness are both located on the X chromosome with no corresponding gene on the Y. Strawberries as they would appear to someone who is red/green colorblind.

45. Sex Linked Traits • Alleles are expressed on each of the sex chromosomes • Female: XAXA or XAXa or XaXa • Male: XAYor XaY Setting up a punnet square for sex-linked traits: Mom= XAXa Dad = XAY XA Xa XA Y

46. Mom is carrier, dad does not have x-linked recessive disorder Mom isn’t carrier, dad has x-linked recessive disorder

47. Sex Linked Traits • Can a female end up with an X-linked trait???? • Example = Sex-linked baldness • assume that baldness (b) is recessive • Full head-o-hair (B) is dominant

48. . Hemophilia is an X-linked recessive disorder characterized by the inability to properly form blood clots.

49. Y Linked Traits

50. Additive effect of two or more genes on a single phenotypic character. Polygenic Inheritance SKIN COLOR Controlled by at least 3 different genes