Genetics

1. Genetics Part 1: Gregor Mendel’s pea plants Part 2: Punnett squares Part 3: More genetics Bonus: Albinism

2. Genetic Traits Widow’s peak

3. Genetic Traits Albinism

4. Genetic Traits Attached and unattached earlobes

5. Genetic Traits Hitchhiker’s thumb Straight thumb

6. Genetic Traits Cleft chin

7. Genetic Traits Tongue roll

8. Genetics Genetics is the scientific study of heredity which is the passing of traits from parents to offspring. • Occurs in all organisms • Through DNA

9. Fertilization • The process in which male and female gametes join to produce a zygote 23 + 23 46 A zygote is a fertilized egg. It starts as one cell and then grows into a new organism.

10. Gametes • Specialized cells involved in sexual reproduction (sex cells) • Ex: sperm (male) eggs (female)

11. 23 23 23 + 23 (gametes) 46(zygote) 46 Gametes • Each gamete contains one set of chromosomes from the parent

12. Gametes • Each gamete contains one set of chromosomes from the parent

13. How do traits get passed down? A gene is a section of DNA that determines a particular trait by coding for specific proteins Ex: eye color gene

14. How do traits get passed down? There are many different eye colors! Possible colors = brown, blue, gray, green, etc.

15. How do traits get passed down? An allele is a specific form of a gene. Example: brown eyes allele blue eyes allele

16. How do traits get passed down? An allele is a specific form of a gene. Example: For the gene for flower color, a pea plant can have a white allele or a purple allele.

17. Mendel’s Principles • Principle of Dominance: Some alleles are dominant and others are recessive. An organism with the dominant allele for a particular trait will always exhibit that trait.

18. Mendel’s Principles • Principle of Dominance: Some alleles are dominant and others are recessive. Dominant: Recessive: Brown hair Red hair Can curl tongue Cannot curl tongue Pigmented skin Albinism Brown eyes Blue eyes

19. How do traits get passed down? Alleles are represented by letters. Examples: B = brown eyes (dominant is uppercase) b = blue eyes (recessive is lowercase) T = tall t = short

20. How do traits get passed down? Organisms have two copies of each gene. BB = brown eyes Bb = brown eyes bb = blue eyes

21. Genetics Genotype: the genetic makeup of an organism (what genes it has) Ex: Bb or bb Phenotype: the physical appearance (what traits it expresses) Ex: brown or blue eyes

22. Genetics Two organisms can have the same phenotype but different genotypes. Ex: Phenotype = brown eyes Possible genotypes = BB and Bb

23. Genetics Homozygous: having two identical alleles for a particular trait Ex: TT or tt (true-breeding) Heterozygous: having two different alleles for the same trait Ex: Tt (hybrid)

24. Gregor Mendel (1822-1884) • Austrian monk • “Father of genetics” • Pea plants

25. Quick Lesson on Plant Reproduction Fertilization: process in which male and female reproductive cells join to produce a zygote

26. male female Quick Lesson on Plant Reproduction • True-breeding peasalways pass on the same traits to offspring (ex: green seeds)

27. 7 different traits  2 forms (alleles) each Seed shape Seed color Seed coat color Pod shape Pod color Flower position Plant height Mendel’s Peas

28. green vs. yellow seeds wrinkled vs. round seeds

29. Mendel’s Peas [Worksheet – front] 1. Dominance 2. Homozygous or Heterozygous?

31. Homozygous or heterozygous?

32. Mendel’s Peas • Crossed plants with contrasting characteristics = parent (P) generation Ex: true-breeding tall plants with true- breeding short plants • Offspring = first filial (F1) generation  Hybrids: offspring of parents with different traits P x PF1

33. Mendel’s Peas What did the F1 generation look like? • All F1 offspring had the trait of onlyone of the parents • The other trait seemed to have disappeared! Where did it go??

34. Principle of Dominance! Some alleles are dominant and others are recessive. In pea plants…

35. Mendel’s Peas So, did the recessive trait just disappear? • Crossed F1 plants with themselves to produce F2 generation • Result: ¼ of F2 plants had recessive trait (3:1 ratio of dominant:recessive)

36. Mendel’s Peas

37. Mendel’s Peas Why did this happen? Offspring receive one allele from each parent. When an F1 plant produces gametes, alleles segregate one copy in each gamete.

38. Bb B b Mendel’s Principles 2. Principle of Segregation: The two alleles for a trait separate during gamete formation. Parent cell Each gamete has only one set of genes. Gametes

39. Bb B b Bb B b BB Bb Bb bb Father Mother The probability of getting each allele is the same (50%).

40. Punnett Squares Punnett squares are diagrams that show gene combinations that might result from genetic crosses.

41. Probability Probability is the likelihood that an event is going to happen. Ex: The probability of picking a queen from a deck of cards is 4/52, or 1/13. Ex: The probability of two parents having a boy is 1/2.

42. Punnett Squares Let’s cross two parents with the following genotypes: BB and bb B B F1 offspring all have Bb genotype. Phenotype? b Bb Bb b Bb Bb

43. Punnett Squares Now let’s cross two of the F1 offspring with each other. F1 cross: B b F2 offspring have genotype ratio of 1 : 2 : 1 (BB : Bb : bb) Phenotype ratio? 3 : 1 B BB Bb b Bb bb

45. Punnett Squares Cross a homozygous tall plant with a heterozygous plant. Tall (T) Short (t) TT x Tt T T What percentage of the offspring will be tall? What percentage of the offspring will be homozygous? T TT TT t Tt Tt

46. Punnett Squares [See worksheet] Single gene crosses with regular dominance

47. Independent Assortment Dihybrid cross:follows the inheritance of TWO traits Ex: seed shape AND seed color

48. Independent Assortment Seed shapeSeed color R = round Y = yellow r = wrinkled y = green

49. Independent Assortment RRYY x rryy (round yellow)(wrinkled green) RrYy (round yellow)

50. Independent Assortment • Try crossing two heterozygous roundyellow peas: RrYy x RrYy • What are the phenotype ratios of the offspring?