Understanding Heredity: Mendel's Experiments and the Relationship Between Traits

1. Chapter 5 Heredity

2. Section 1: Objectives • Explain the relationship between traits and heredity. • Describe the experiments of Mendel. • Explain the difference between dominant and recessive traits.

3. Heredity • Heredity: passing of traits from parent to offspring • Gregor Mendel was one of the first scientists to study heredity. • What are traits?

4. Heredity • Gregor Mendel was born in 1822 in Austria. • He grew up on a farm where he learned about flowers and fruit trees. • He entered a monestary when he was 21 years old.

5. Heredity • Here, he was taught science and performed many scientific experiments. • He put most of his energy into research. • Mendel discovered the principles of heredity.

6. Heredity • From working with plants, Mendel knew the patterns of inheritance weren’t always clear. • For example, sometimes a trait may be expressed in offspring that was not expressed in either parent.

7. Heredity • Mendel wanted to learn more about what caused these patterns. • To keep it simple, he studied 1 type of organism: pea plants. • Why would studying 1 organism at a time be helpful in studying patterns of inheritence?

8. Heredity • Pea plants were a good choice for several reasons: • They grow quickly • There are many different kinds • They are self pollinating • A self pollinating plant has both male and female structures.

9. Heredity • Pollen from one plant can fertilize the ovule of the same plant. • Mendel was able to grow true-breeding plants. • In true-breeding plants, the offspring have the same traits as the parent.

10. Heredity • Pea plants can also cross-pollinate. • In cross-pollination, pollen from one plant fertilizes another plant. • Pollen can be carried by: • Insects • Wind

11. Heredity • Mendel studied only 1 characteristic at a time. • A characteristic is a feature that has different forms in a population. • For example, hair color is a characteristic; different forms such as red hair or brown hair is a trait.

12. Heredity • Mendel’s first experiments: • Mendel crossed pea plants to study 7 different characteristics. • The trait that appeared most of the time was called the dominant trait. • The recessive trait was the trait that appeared less.

13. Heredity • Mendel’s Second Experiments: • Mendel allowed the first generation plants to self-pollinate. • He completed the exact same experiment for each of the 7 characteristics he was studying.

14. Heredity • Mendel studied each of the following characteristics: • Flower color • Seed color • Seed shape • Pod color • Pod shape • Flower position • Plant height

15. Heredity • A ratio is a relationship between 2 different numbers. • Mendel calculated the ratio for dominant to recessive traits. • Make a fraction: Dominant/Recessive

16. Heredity • Ratio Example: Dominant = purple flowers Recessive = white flowers 705 purple: 224 white Ratio = 3.15:1

17. Calculate the Following Ratios • A) 6,002 yellow: 2,001 green • B) 5,474 pink: 1,850 red • C) 428 green: 152 yellow • D) 787 short: 277 tall • What do these ratios have in common?

18. Punnett Square Rules Goal: Predict traits for offspring by looking at traits for both parents Pick one letter to represent the dominant and recessive trait. Dominant traits – capital letter Recessive traits – lower case

19. Punnett Square Rules Genotype refers to the organism’s gene combination. Phenotype refers to the way an organism looks. Ratio is a comparison of the dominant to recessive traits. Dominant/Recessive = Ratio Example = 75/25 = 3:1 Example = 50/50 = 1:1

20. Punnett Square Rules After reading the problem, pick a genotype for the parents. These will always have 2 letters because the letters represent paired chromosomes. Next set up your Punnett square and make your cross. Analyze your Punnett square in order to complete the genotype, phenotype, and ratio.

21. Chapter 5 Sec. 1 Recap 1) What is Gregor Mendel famous for? 2) What type of plants did Mendel study? 3) Explain the difference between a self and cross pollinating plant. 4) What is a ratio? 5) Describe Mendel’s 1st experiments.

22. Example # 1 Purple flower color is dominant in pea plants. Cross a dominant purple flowered plant with a recessive white flowered plant. PP x pp Genotype: ? Phenotype: ? Ratio: ?

23. Example # 2 In beagles, long ears are dominant over short ears. Cross a dominant long eared beagle with a recessive short eared beagle. Genotype: LL x ll Phenotype: Long eared x short eared Ratio: ?

24. Example # 3 In frogs, long legs are dominant to short legs. Cross a long legged bullfrog with a short legged bullfrog. Genotype: LL x ll Phenotype: Long legged x short legged Ratio: ?

25. Example # 4 In chickens, white feathers are dominant to brown feathers. Cross a dominant white feathered chicken with a recessive brown feathered chicken. Genotype: Phenotype: Ratio:

26. Example # 5 In cats, short whiskers are dominant to long whiskers. Cross 2 recessive long whiskered cats. Genotype: Phenotype: Ratio:

27. Example # 6 In mice, pink noses are dominant to black noses. Cross 2 dominant pink nose mice. Genotype: Phenotype: Ratio:

28. Example # 7 In sheep, curly wool is recessive to straight wool. Cross a sheep with curly wool with a sheep that has straight wool. Genotype: Phenotype: Ratio:

29. Example # 8 In bullfrogs, green skin color is dominant to brown skin color. Cross 2 bullfrogs that have brown skin color. Genotype: Phenotype: Ratio:

30. Analyzing Genetic Crosses 1) What is an organism’s genotype? 2) What is an organism’s phenotype? 3) How do you determine a ratio? 4) How are dominant traits different from recessive traits? 5) What do the letters represent in a genetic cross? 6) Why are there 2 letters that represent each organism?

31. Homozygous vs. Heterozygous Homozygous – having both of the same genes Heterozygous – having one of each gene Ex) Heterozygous – Pp Ex) Homozygous – PP, pp

32. Complete the Following Cross • In daisies, yellow flower color is dominant over white. Cross a homozygous yellow flowered plant with a homozygous white flowered plant. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

33. Complete the Following Cross • Pick any 2 offspring from the last slide and complete a cross. Dominant and recessive traits remain the same. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

34. Complete the Following Cross • In crimson clover, red flowers are dominant over pink. Cross a heterozygous red crimson clover plant with a homozygous pink crimson clover plant. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

35. Complete the Following Cross • Pick any 2 offspring from the last slide and complete a cross. Dominant and recessive traits remain the same. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

36. Complete the Following Cross • In grapes, purple color is dominant over green. Cross a heterozygous purple colored grape plant with a homozygous green colored grape plant. • 1) Offspring Genotype (include percentages) • 2) Offspring Phenotype (include percentages) • 3) Ratio of dominant to recessive traits:

37. Complete the Following Cross • Pick any 2 offspring from the last slide and complete a cross. Dominant and recessive traits remain the same. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

38. Chapter 5 Sec. 1 Review • 1) __________ was one of the first scientists to study heredity. • 2) What is the difference between self-pollination and cross pollination? • 3) What type of plants did Mendel study? • 4) What is a characteristic? • 5) What is a ratio? • 6) How many characteristics did Mendel study?

39. Section 2: Objectives • Explain how genes and alleles are related to genotype and phenotype. • Use the information in a Punnett square. • Explain how the probability can be used to predict possible genotypes in offspring. • Describe 3 exceptions to Mendel’s observations.

40. Phenotype vs. Genotype • The first generation carries the instructions for both dominant and recessive traits. • Scientists now call these instructions genes, one set of instructions for an inherited trait. • The different forms of a gene are alleles.

41. Phenotype vs. Genotype • Genes affect the traits of offspring. • An organism’s appearance is known as phenotype. • Examples: Red flower color, white flower color, yellow flower color

42. Phenotype vs.Genotype • Both inherited alleles together form an organism’s genotype. • Heterozygous: one dominant and one recessive trait (Rr) • Homozygous: 2 dominant or 2 recessive traits (RR or rr)

43. Phenotype vs. Genotype • Probability: “The mathematical chance that something will happen” • In a coin toss, you have a 50% chance of getting heads or tails. • This is the case with inherited traits as well.

44. Phenotype vs. Genotype • Probability is written as a fraction or percentage. • If you toss a coin, the probability of tossing tails is 50%. (You will get tails half the time.)

45. Probability Example • If you roll a pair of dice, what is the probability you will roll 2 threes separate times? • Count the number of faces on the dice. Put this number in the denominator. (6) • Count the number of ways you can roll 3 with one dice. Put this number in the numerator. (1)

46. Probability Example • To find the probability that you will throw 2 threes, multiply the probability of throwing the first 3 by the probability of throwing the second 3: 1/6 X 1/6 = 1/36.

47. Probability Example # 2 • What is the probability that you will roll an even number with one dice? • Count the number of faces on the dice (denominator) • Count the number of ways you can roll an even number. (numerator)

48. Genetic Cross # 5: Part A • In goldfish, wide tails are dominant over narrow tails. Wide tails are dominant because they require the goldfish to use less energy while swimming. Cross a homozygous dominant goldfish with a heterozygous goldfish. • 1) Offspring Genotype (%) • 2) Offspring Phenotype (%) • 3) Ratio (Dominant to recessive traits)

49. Genetic Cross # 5: Part B • Pick any 2 offspring from the last slide and complete a cross. Dominant and recessive traits remain the same. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

50. Genetic Cross # 6: Part A • In sheep, curly wool is dominant over straight wool. Cross a homozygous curly sheep with a homozygous non-curly sheep. • 1) Offspring Genotype (%): • 2) Offspring Phenotype (%): • 3) Ratio: (dominant to recessive traits)