Understanding Mendelian Genetics: Traits, Crosses & Predictions

1. Mendelian Genetics Gregor Mendel

2. Introduction • Genetics is the study of heredity • Gregor Mendel used mathematics to study the inheritance of traits

3. Phenotypes • These are features you exhibit physically ( your looks) Example: Eye color - green

4. Alleles • The different versions of a characteristic • Example: blue, green, and brown eyes

5. Inheritance • Occurs when traits are passed down from parent to child. • Gametes (sex cells like sperm or ovaries) carry traits to offspring.

6. Genes • Bits of information passed down from parent to child. • Made of chemicals called DNA.

7. Heredity • The chromosome theory of heredity states that the inheritance of traits is controlled by genes, located on chromosomes

8. Key Terms • Genotype - gene combination for a trait(e.g. RR, Rr, rr) • Phenotype - the physical feature resulting from a genotype(e.g. red, white)

9. The Average American Phenotype

10. Alleles • T – is considered a dominant allele • t – is considered a recessive allele TT – is homozygous dominant Tt or tT – is heterozygous dominant tt - is Homozygous recessive recessive

11. Genotype & Phenotype in Flowers Genotype of alleles:R= red flowerr= yellow flower All genes occur in pairs, so 2alleles affect a characteristic Possible combinations are: GenotypesRRRrrr PhenotypesRED RED YELLOW

12. The Law of Dominance • Law states that the dominant allele, if present, will be expressed. • Dominant - stronger of two genes expressed in the hybrid; represented by acapital letter (R) • Recessive - gene that shows up less often in a cross; represented by alowercase letter (r)

13. Predicting traits • Probability is used to predict traits in offspring • Punnett squares are diagrams used to predict outcomes from a cross

14. Types of Genetic Crosses • Monohybrid cross - cross involving a single traite.g. flower color • Dihybrid cross - cross involving two traits e.g. flower color & plant height

15. How to do a monohybrid cross

16. Law of Segregation • During the formation of gametes (eggs or sperm) during meiosis, the two alleles responsible for a trait separate. • Alleles for a trait are then "recombined" at fertilization.

17. Applying the Law of Segregation

18. Make a Cross for the following: • Imagine you are crossing two vampire bats. • The dominant trait for skin color is black (S). • The recessive trait for skin color is white (s). • It you have one parent with the genotype Ss and one with the genotype ss, what kind of offspring would they have? S s s s

19. Answer S s s s

20. Group Assignment • Let’s imagine we found a new species of dog called a Gir. • We are going to practice crossing this new species to get a better knowledge of how Punnett Squares work. A pure breed GREEN Gir has the genotype GG A pure breed RED Gir has the genotype gg A Gir with the genotype Gg will have a GREEN phenotype because green is dominant over red.

21. g g G G Breed the P1 generation • Green (GG) x Red (gg)

22. g g produces the F1 generation Gg Gg G Gg Gg G All Gg = Green (heterozygous Green) Solution: Green (GG) x Red (gg) dogs

23. G g G g Breed the F1 generation • Green (Gg) x Green (Gg)

24. G g produces the F2 generation Gg GG G 1/4 (25%) =GG 1/2 (50%) =Gg 1/4 (25%) = gg Gg gg g 1:2:1 genotype 3:1 phenotype Solution: Green (Gg) x Green (Gg)

25. X X X Y Punnett Squares can also be used to determine the sex. XX XX 50% possibility of female XX XY XY 50% possibility of male XY

26. Dihybrid Cross • A breeding experiment that tracks the inheritance of two traits. • Follows Mendel’s “Law of Independent Assortment” • Each pair of alleles segregates independently during gamete formation

27. Dihybrid Cross • Traits: Seed shape & Seed color • Alleles: R round r wrinkled Y yellow y green shape color RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations

28. Law of Independent Assortment • Alleles for differenttraits (like eye color and hair color) are distributed to sex cells (& offspring) independently of one another.

29. RY Ry rY ry RY Ry rY ry Dihybrid Cross

30. Dihybrid Cross Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1 9:3:3:1

31. Pedigrees • Pedigrees use symbols to track a trait. • Trait is then tracked through generations.

32. Example Generation 1 Generation 2 Generation 3

33. Pedigree • Pedigree: is a diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships. • These diagrams make it easier to visualize genetic relationships within families. • Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases.

34. Incomplete DominanceandCodominance

35. r r R R Incomplete Dominance • F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. • Example:snapdragons (flower) • red (RR) x white (rr) • RR = red flower • rr = white flower

36. r produces the F1 generation Rr Rr R R Rr Rr All Rr = pink (heterozygous pink) Incomplete Dominance r

37. Incomplete Dominance

38. Codominance • Multiple alleles are expressed in heterozygous individuals. • Example: blood type • 1. type A = IAIA or IAi • 2. type B = IBIB or IBi • 3. type AB = IAIB • 4. type O = ii A and B are types of antigens. O type blood does not have these antigens.

39. IA i IB What blood types are possible in offspring? IB Codominance Problem • Example: Type B (IBIB) x Type A (IAi)

40. IA i IAIB IBi IB 1/2 = IAIB 1/2 = IBi IB IAIB IBi Codominance Problem • Example: Type B (IBIB) x Type A (IAi)

41. IA IB i What are the possible blood types? i Another Codominance Problem • Example:male Type O (ii) x female type AB (IAIB)

42. IA IB IAi IBi i 1/2 = IAi 1/2 = IBi i IAi IBi Another Codominance Problem • Example:male Type O (ii) x female type AB (IAIB)

43. Sex-linked Traits • Traits (genes) located on the sex chromosomes • Sex chromosomes are X and Y • XX genotype for females • XY genotype for males • Many sex-linked traits carried on X chromosome ONLY. • Color blindness, Hemophilia (can’t clot blood), Kabuki syndrome, baldness • This means males get genes on X gene from MOTHER.

44. fruit fly eye color XX chromosome - female Xy chromosome - male Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes

45. Xr Xr XR Y Sex-linked Trait Problem • Example: Eye color in fruit flies • (red-eyed male) x (white-eyed female)XRY x XrXr • Remember: the Y chromosome in males does not carry traits. • RR = red eyed • Rr = red eyed • rr = white eyed • XY = male • XX = female

46. Xr Xr XR Xr XR Xr XR Y Xr Y Xr Y Sex-linked Trait Solution: 50% red eyedfemale 50% white eyed male

47. Alien Lab • You will spend 2/3 class periods creating this booklet. • DO NOT LOSE YOUR BOOKLET. • TURN IT IN TO ME after each class period so you won’t lose it. • There are NO EXTRA COPIES.

48. You will create a booklet of an Alien you create and its FAMILY HISTORY in terms of genetics. EVERYONE will have a DIFFERENT alien. • Things to complete (look at rubric on page 11) • 1. Cover page (Day 1) • 2. Alien Trait Key (Day 1) • 3. Alien Personal Data (Day 1) • 4. Alien Personal Ad (Day 2) • 5. Alien Mate Data Sheet (Day 2). • 6 & 7 Alien Matchmaking Traits (Day 2) • 8. Alien Offspring Trait Key (Day2/3) • 9. Alien Offspring Drawings (Day 3) • 10. Discussion Questions (Day 3) I will discuss each thing the DAY we will do them. I will only cover items 1-3 today.

49. Alien Trait Key • We will do this AS A CLASS. • We will discuss what we want our ALIEN SPECIES TO LOOK LIKE.