Genetics

1. Genetics Why You Look the Way You Do George RadcliffeCentreville Middle SchoolApril, 2008

2. CONTENTS • Vocabulary • Asexual Reproduction • Sexual Reproduction • Mitosis vs. Meiosis • The Gene • Genotypes and Phenotypes • Punnett Square – Predicting Offspring • Practice Problems • Review Quiz

3. VOCABULARY YOU NEED TO BE ABLE TO SPEAK “GENETICS” • Asexual reproduction • Sexual reproduction • Mitosis– normal cell division • Meiosis • Gamete • Fertilization • Pollination • Gene • Trait • Allele • Dominant • Recessive • Genotype • Phenotype • Homozygous • Heterozygous • Punnett Square

4. Asexual Reproduction • The gene is a strand of DNA that makes a particular protein, enzyme, or pigment. • In asexual reproduction, all of the DNA comes from your 1 parent. • If an asexually reproducing plant had yellow flowers, what percentage of its offspring will have yellow flowers? • Answer: 100% of the offspring will have yellow flowers. Contents

5. The Gene and Sexual Reproduction • The gene is a strand of DNA that makes a particular protein, enzyme, or pigment. • ½ of your DNA comes from the mother’s egg. • ½ comes from the father’s sperm. • These half cells are produced by the process of meiosis. • Each of these ½ cells (egg, sperm or pollen) is called a gamete. • When the two halves combine (fertilization) you have a complete set of DNA. (½ + ½ = 1) • Thus you actually have two of each gene. Vocabulary

6. Plants and Sexual Reproduction • Plants usually reproduce sexually, too. • The female half of the DNA is found in the egg. • The male half comes from the pollen. • Insects or wind carries the pollen from one flower to another. This pollination leads to fertilization of the egg. • This fertilized egg is called a zygote. The zygote has a complete set of DNA. Contents Vocabulary

7. Mitosis vs. Meiosis • Go to the following PBS website listed below. Either run the flash animation, or use the non-Flash version. • Answer: how is meiosis different from mitosis? • Link: PBS Meiosis/Mitosis Site

8. Mitosis vs. Meiosis • How is meiosis different from mitosis? • Answer: In the beginning, they are the same, one cell dividing into two complete cells. In meiosis the two cells then each divide into 2 half cells. • If you missed this, go back (hit “P”), and run the animation again.

9. Comparison of meiosis and mitosis Mitosis Meiosis Makes gametes Makes 2 copies of any cell Makes eggs, sperm, pollen Produces two cells Produces four gametes 46 chromosomes 23 pairs 23 chromosomes 1 from each pair

10. Let’s See if We’ve Got it All Straight. • Question: What is the process that produces normal cells? • Answer: Mitosis • Question: What is the process that produces eggs, sperm, and pollen? • Answer: Meiosis • Question: What is a gamete? • Answer: a sex cell: egg, sperm, or pollen • Question: How much DNA does a pollen or egg have? • Answer: ½ of the normal DNA • Question: How much DNA does a zygote have? • Answer: full amount of DNA

11. The Gene • Let’s see how genes work. • Let’s look at human eye color. • The gene is represented by the letter B. • There are 2 alleles for this gene; that means that there are 2 ways that eye color can be. • Eye color can be brown; we show this gene with a B. • Eye color can also be blue; we show this gene with a b. • Remember: You get a gene from each parent; so you have 2. Vocabulary Contents

12. Which Gene Does Your Cell Listen to? • If you have 2 brown genes (BB), your eyes are obviously brown. • If you have 2 blue genes (bb), your eyes are obviously blue. • But what happens if you have one of each gene? • The dominant gene wins out. • Brown (B) is the dominant gene; that’s why it is represented with a capital letter. • Thus a person with Bb genes has brown eyes. • The blue gene (b) is recessive; that means it is hidden or masked by the dominant gene, BUT it can be passed on to the offspring. Vocabulary Contents

13. Genotypes and Phenotypes • Let’s show this in a chart. • Trait: Eye color • Alleles:B and b Vocabulary Contents

14. Genotypes and Phenotypes • Let’s look at another trait. • Trait: Height of a pea plant • Alleles: T and t • T – gene for tallness t – gene for short plant

15. Let’s Review • Question: What is the trait? • Answer: height of pea plant • Question: What are the alleles for height? • Answer: T and t • Question: What is the dominant allele? • Answer: T

16. Let’s Review • Question: What is genotype for a short plant? • Answer: tt • Question: What is the phenotype for TT? • Answer: tall • Question: What is the phenotype for Tt? • Answer: tall since T is dominant Contents

17. Genotype and Phenotype Practice Let’s do some practice using the 4 pairs of pea plant genes shown at the right. For each genotype listed, give the phenotype (what it looks like). T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas green leaves yellow leaves

18. Genotype and Phenotype Practice T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas purple flowers wrinkled peas round peas tall plants with green leaves purple flowers and wrinkled peas tall plants, yellow peas, white flowers, and round peas Contents

19. Homozygous and Heterozygous • Let’s add 2 more words to the mix. • Homozygous means both genes are the same. • Heterozygous means both genes are different, • “Homo” = the same “Hetero” = different • “zygous” refers to the zygote, the first cell formed from the fertilization of the egg by the sperm. • Another word for a heterozygous (Tt) is hybrid, one of each gene). Vocabulary Contents

20. Putting it All Together • What is the homozygous genotype for a tall plant? • Answer: TT • What is the heterozygous genotype for a tall individual? • Answer: Tt • What is the heterozygous genotype for a short individual? • Answer: impossible; Tt is can’t be short.

21. Monohybrid inheritance Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled seeds be: r (recessive allele) Parents phenotyperound seeds x round seeds genotype RRRR Gametes (pollen, eggs) Offspring R R R R We call this a Punnett Square. We’ll use this to show the 4 ways that the gametes from the 2 parents can combine.

22. Monohybrid inheritance • Let’s watch this in action. • With these gametes, there are 4 possibilities; that’s why there are 4 boxes in the Punnett Square. Possibility # 1 R R R R

23. Monohybrid inheritance • Let’s watch this in action. • With these gametes, there are 4 possibilities; that’s why there are 4 boxes in the Punnett Square. Possibility # 2 R R R R

24. Monohybrid inheritance • Let’s watch this in action. • With these gametes, there are 4 possibilities; that’s why there are 4 boxes in the Punnett Square. Possibility # 3 R R R R

25. Monohybrid inheritance • Let’s watch this in action. • With these gametes, there are 4 possibilities; that’s why there are 4 boxes in the Punnett Square. Possibility # 4 R R R R

26. Monohybrid inheritance Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled seeds be: r (recessive allele) Parents phenotyperound seeds x round seeds genotype RRRR Offspring All possibilities are the same: RR. Offspring phenotypes100% plants producing round seeds Offspring genotypes 100% heterozygotes RR

27. Monohybrid inheritance – Part 2 Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled seeds be: r (recessive allele) Parents phenotypewrinkled seeds x wrinkled seeds genotype rrrr Gametes (eggs, pollen) Offspring r r r r Offspring phenotypes 100% plants producing wrinkled seeds Offspring genotypes 100% heterozygotes rr

28. Monohybrid inheritance – Part 3 Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled seeds be: r (recessive allele) Parents phenotyperound seeds x wrinkled seeds genotype RRrr Gametes Offspring r r R R Offspring phenotypes 100% plants producing round seeds Offspring genotypes 100% heterozygotes Rr

29. Contents Heterozygous Cross Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled seeds be: r (recessive allele) Parents phenotyperound seeds x round seeds genotype RrRr Gametes Offspring R r R r Offspring phenotypes 75% plants producing roundseeds 25% plants producing wrinkled seeds Offspring genotypes 50% Rr 25% RR 25% rr

30. Prediction vs. Actual • Predicted Offspring phenotypes75% plants producing round seeds • 25% plants producing wrinkled seeds • Ratio 3:1 Round seeds: wrinkled seeds • This is what we predict, just like we predict that 1 out of 2 coin flips will be heads. • Actual results can be different. • If we bred the plants above many times, we would at least get close to a 3:1 ratio. Contents

31. Prediction vs. Actual • To see how predicted can vary from what actual happens. Let’s look at coin flips. • Because there is a 50:50 chance of heads turning up, ½ or 50% of coin flips will be heads. • This obviously doesn’t happen, but if you flip the coin enough, you will approximate 50%. • Go to the website below, and flip coins different numbers of time. Notice that when you flip 10,000 times, you will always get close to 50%. • Return here when you’re done. • Go to Coin Toss Probability Contents

32. If plant is homozygous dominant RR Parents phenotype round x wrinkled genotype RR rr gametes Offspring If plant is heterozygous Rr Parents phenotype round x wrinkled genotype Rr rr gametes Offspring How can you tell if a parent is RR or Rr?To test whether a plant producing round seeds is homozygous RR or heterozygous Rr it can be crossed with a homozygous rr plant R r r r R R r r Offspring phenotype 100% round Genotype 100% Rr Offspring phenotype 50% round/50% wrinkled genotype 50% Rr 50% rr

33. Let’s Try a Couple Problems! Two plants are cross pollinated: Gg and gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas • What percentage of the plants will be yellow? • What is the ratio of green to yellow plants?

34. Let’s Try a Couple Problems! Two plants are cross pollinated: Gg and gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas • What percentage of the plants will be yellow? 50% • What is the ratio of green to yellow plants?1:1 ratio of green: yellow

35. Practice Problem #2 Two plants are cross pollinated: Gg and Gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas • What percentage of the plants will be green? • What is the ratio of green to yellow plants?

36. Practice Problem #2 Two plants are cross pollinated: Gg and Gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas • What percentage of the plants will be green? 75% • What is the ratio of green to yellow plants?3:1 ratio of green: yellow

37. Practice Problem #3 Two plants are cross pollinated: GG and gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas • What percentage of the plants will be yellow?

38. Practice Problem #3 Two plants are cross pollinated: GG and gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas • What percentage of the plants will be yellow? 0%

39. Practice Problem #4 Two plants are cross pollinated: Pp and Pp. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas • What percentage of the plants will be white? • What is the ratio of purple to white flowers?

40. Practice Problem #4 Two plants are cross pollinated: Pp and Pp. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas • What percentage of the plants will be white? 25% • What is the ratio of purple to white flowers?3:1 ratio of purple: white Contents

41. Review Questions • Number a ¼ sheet of paper from 1 to 15. • Answer the questions with no assistance. • Score your paper with the key; consider 11 or more correct as OK. • Go back into the PowerPoint to correct your errors.

42. Review Questions 1. What process produces the gametes? • fertilization • mitosis • conjugation • meiosis

43. Review Questions 2. In asexual reproduction • Gametes are produced. • Fertilization occurs. • An identical cell is produced. • A cell with ½ of the DNA is produced.

44. Review Questions 3. In sexual reproduction, meiosis produces • A zygote. • A cell with ½ of the DNA • A cell with double the DNA • A cell with the same DNA as the parent’s cell.

45. Review Questions 4. A plant with Tt genes reproduces asexually. What will its offspring look like? • None will be tall. • 50% will be tall. • 75% will be tall. • 100% will be tall.

46. Review Questions 5. What is the genotype of a homozygous tall plant? • TT • Tt • tt • None of the above T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas

47. Review Questions 6. What is the phenotype of a Gg plant? • Green leaves • Yellow leaves • Green and yellow leaves • It depends on who gave the G gene. T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas

48. Review Questions 7. Which of the below could be the genotype for a plant with purple flowers? • PP • Pp • Either PP or Pp • Neither PP or Pp T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas

49. Review Questions 8. Which of the below could be the genotype for a short plant with purple flowers? • TtPP • ttPp • TTpp • Ttpp T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas

50. Review Questions 9. A cutting is taken from a pea plant. Thus the plant reproduces asexually. The parent has TtGg genes. What percentage of the offspring will be tall with yellow leaves? • 100% • 50% • 25% • 0% T = tall t = short G = green leaves g = yellow leaves P = purple flowers p = white flowers R = round peas r = wrinkled peas