Understanding Mendelian Genetics: Traits, Inheritance, and Hybridization

1. Intro to Genetics

2. True-breeds:pure gene lines – offspring match parent Self-pollination:pollen from flower fertilizes the same plant Cross-pollination:pollen will fertilize a different plant Hybrid:Cross between organisms with different traits (blonde hair & brown hair) Trait:Physical characteristics Background Vocabulary

3. Austrian monk “Father of Modern Genetics” Famous for his work with peas Gregor Mendel

4. Mendel’s Peas

5. Cross-Pollinating

6. TRAIT 1: Seed Shape P Cross: Round v. Wrinkled F1 Phenotype: Round Mendel’s Crosses

7. TRAIT 2: Seed Color P Cross: Green v. Yellow F1 Phenotype: Yellow Mendel’s Crosses

8. TRAIT 3: Flower Color P Cross: Purple v. White F1 Phenotype: Purple Mendel’s Crosses

9. TRAIT 4: Pod Shape P Cross: Inflated v. Pinched F1 Phenotype: Inflated Mendel’s Crosses

10. TRAIT 5: Pod Color P Cross: Green v. Yellow F1 Phenotype: Green Mendel’s Crosses

11. TRAIT 6: Flower Position P Cross: Axial v. Terminal F1 Phenotype: Axial Mendel’s Crosses

12. TRAIT 7: Plant Height P Cross: Tall v. Short F1 Phenotype: Tall Mendel’s Crosses

13. Mendel’s Conclusions • Biological inheritance is determined by chemical factors passed from one generation to the next (Particulate hypothesis) • Geneticists now refer to these factors as genes • Genes can come in more than one form, each form is an allele ex. B or b (The “B” gene w/ 2 alleles)

14. The Principle of Dominance • Certain alleles will be expressed over others • The expressed alleles are dominant to the unexpressed recessive alleles

15. The F1 Cross • Mendel’s experiment: • Allow the F1 plants to self pollinate • The results: • The dominant trait was expressed 75% of the time • The recessive trait was expressed 25% of the time

16. The Explanations: 1. The recessive allele was still present in the F1 plants 2. Principle of Segregation: Each individual inherits two alleles for each gene.

17. Probability • The likelihood of an event happening • How is it determined: • Likelihood of rolling heads = 50% (1 of 2 possibilities) • Rolling heads twice? • 50% x 50% = 25% • To predict outcomes of genetic crosses we use punnett squares

18. More genetics vocabulary… • Homozygous: two identical alleles (AA or aa) • Heterozygous: two different alleles (Aa) • Phenotype: Physical appearance • Genotype: Genetic make-up • Homozygous dominant (AA) • Homozygous recessive (aa) • Heterozygous (Aa)

19. The Test Cross • In order to determine whether an individual expressing a dominant trait is homozygous or heterozygous, it can be crossed with an organism expressing the recessive trait. • If R = round seeds and r = wrinkled seeds, show how the results of a test cross for seed shape will differ for homozgygous v. heterozgous genotypes for round seeds.

20. Monohybrid (1-factor) Cross Practice KEY: G = green pods, g = yellow pods P = purple flowers, p = white flowers T = tall plants, t = short plants Show a cross a plant heterozygous for green pods with a plants with yellow pods. What are the expected genotype and phenotype ratios? Show a cross of a homozygous tall plant with a heterozygous tall plant. What are the expected genotype and phenotype ratios? Show a cross of two heterozygous purple flowered plants. What are the expected genotype and phenotype ratios?

21. Exploring Mendelian Genetics • Does segregation of one set of alleles influence the segregation of another pair of alleles? • Mendel’s Two Factor Crosses • Followed two traits at a time. • Same method as his original single-factor crosses • Cross-pollinated to produce the F1 and allowed them to self-pollinate

22. The Parental Cross _________________________________

23. The F1 Cross _________________________________

24. A Summary of Mendel’s Principles • Dominance: a recessive allele will be masked by a dominant allele • Segregation: alleles for each trait segregate (separate) during gamete formation • Independent Assortment: Alleles for different traits do not influence each other’s segregation

25. Mendel’s Peas were ideal for learning about inheritance, but they do not represent the norm… • Traits in pea plants are determined by just two alleles • In peas, one allele is clearly dominant & the other is clearly recessive • However, things aren’t always this clear-cut and simple in the world of genetics.

26. What if Mendel looked at mice? • If a female black mouse and a male white mouse were crossed, what will the offspring look like? - 100% are GREY • If the F1 offspring were crossed, what will there offspring look like? - 25% black - 50% grey - 25% white

27. Incomplete Dominance • A cross between two organisms with different traits results in an offspring with a third phenotype that is a blending of the parental traits. • It’s like mixing paints: • Red+ White =Pink • Red does not totally block (dominate) white, we end up with something in-between.

28. Inheritance in Snapdragons

29. Let’s try crossing snapdragons… What will the genotype and phenotype ratios be if a red plant is crossed with a pink plant? (Use the following allele symbols: CR & CW) G: P:

30. What does the prefix “Co-” mean? • Consider the meaning of the following words: - Cooperate - Coexist - Cohabitat • What about “Codominance”?

31. Let’s look at cattle…. This cow resulted from a cross between a cow with red fur and a cow with white fur. This is called ‘roan’ fur; red & white fur together.

32. Codominance • Similar to incomplete dominance in that there is a 3rd phenotype • In COdominance, the “recessive” and “dominant” alleles appear together in the phenotype of hybrid organisms. • Red x White = red & white

33. Let’s try crossing cattle…. What will the gentype and phenotype ratios be if a red cow is crossed with a white cow? G: P:

34. Polygenic (Multifactorial) Traits • Phenotype is determine by more than one gene • Often results in gradations, where each gene has an additive effect Ex) If 10 gene loci are turned on plant will be 20cm tall, if only 5 loci are turned on plant will be 10cm tall • Results in a bell-shaped curve • Skin color & Height are examples in humans

35. Phenotype Distribution:Polygenic Traits

36. Multiple Alleles • More than 2 alleles for a particular trait KEY C = full color; dominant to all other alleles cch= chinchilla; partial defect in pigmentation; dominant to ch and c alleles ch = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles Full color: CC, Ccch, Cch, or Cc Chinchilla: cchch, cchcch, or cchc Himalayan: chc, or chch AIbino: cc

37. ABO Blood Types • In addition to having multiple alleles, ABO blood type also exhibits codominance • ‘IA’ & ‘IB’ are codominant • ‘i’ is recessive

38. ABO Blood Typing

39. What does your ABO blood type mean? • Remember the ‘flags’ on our cell membranes? They help cells to recognize each other. • Some of those flags ‘announce’ your blood type. We call these flags antigens

40. ABO Blood Transfusions

41. Summary of ABO Blood Types

42. Rh Factor • Blood can also be categorized as + or – • This refers to the presence (dominant) or absence (recessive) of the Rh antigen

43. Rh Factor & Pregnancy

44. Rh Disease • Mother's antibodies cross the placenta to fight the • Rh positive cells in the baby's body. • As the antibodies destroy the red blood cells, the baby can • become anemic. • The anemia can lead to other complications including jaundice and organ enlargement • With amniocentesis, the amniotic fluid may have a yellow coloring and contain bilirubin. • Ultrasound of the fetus shows enlarged liver, spleen, or heart and fluid build up in the fetus' abdomen.

45. Gene Linkage & Mapping Chromosomes • Genes on the same chromosome are more likely to be inherited together • Crossing over helps to increased variation, but the closer two genes are on a chromosome the more likely they are to be “linked”

46. Sex Chromosomes & Autosomes • Two of the 46 human chromosomes are known as sex chromosomes, because they determine the individual’s sex. • Females have two copies of an X chromosome. • Males have one X chromosome and one Y chromosome. • The remaining 44 chromosomes are known as autosomal chromosomes or autosomes.

47. Located on one of the sex chromosomes (X or Y) Since the X chromosome is longer, it has many genes not found on the Y chromosome. Most sex-linked genes are X-linked genes. Sex-Linked Genes

48. Sex-Linked Genes

49. Possible Inheritance of Colorblindness Allele

50. Calico/Tortioseshell Cats • There is a fur color gene located on the X chromosome in cats. • For tortoiseshell there are two possible alleles, orange and black, which are codominant in a heterozygote • For calico there are also codominant black and orange alleles, but they code for blotches on a white background. Are these cats male or female? Explain.