Fundamentals of Genetics

1. Fundamentals of Genetics This is a Ms. Brown educational production

2. Introduction • The Audience: • This project is intended for the 9th and/or 10th grade high school biology student. • The Objective: By the end of this tutorial you will be able to: • Determine the genotype and phenotype of monohybrid crosses using a punnett square • Explain how offspring inherit traits from their parents

3. New Vocabulary • Genetics • Heredity • Trait • Gene • Allele • Dominant • Recessive • Genotype • Phenotype • Probability • Gametes • Parental (P) Generation • 1st Filial (F1) Generations • 2nd Filial (F2) Generations • Cross Pollinate • Self Fertilization • Monohybrid • Dihybrid • Heterozygous • Homozygous

4. Genetic Terminology • Genetics-The scientific study of heredity • Heredity- Passing of traits from parents to offspring • Trait- any characteristic that can be passed on from parent to offspring (ex. Pea plant color, shape, length, etc.)

5. Genetic Terminology • Gene- Segment of DNA for trait expression • Allele- Each of the alternative forms of a gene (ex. dominant or recessive)

6. Genetic Terminology • Dominant- Masks the other allele, represented by Capital Letter (ex. Y) • Recessive- The masked allele, represented by lowercase letter (ex. y) • Genotype- Genetic make up of the organism (ex. YY, Yy, or yy) • Phenotype- Appearance of an organism due to genotype (ex. Yellow or green seed color)

7. Genetic Terminology • Monohybrid Cross- The crossing of one characteristic (ex. YY x yy) • Dihybrid Cross- The crossing of two characteristics (ex. YYRR x yyrr) • Heterozygous genotype- Two different alleles (ex. Yy) • Homozygous genotype- Two alleles that are the same (ex. YY or yy) • Probability-The likelihood of an event to occur

8. Genetic Terminology • P Generation- The original parental cross • 1st Filial Generation- The offspring of the parent generation • 2nd Filial Generation- The offspring of the F1 generation • Cross Pollination- reproduction occurs between two flowers (sexual) • Self-Fertilization- reproduction occurs in the same flower (asexual)

9. Genetics & Probability

10. Genetics & Probability • The likelihood that a particular event will occur is called Probability. • The principles of probability can be used to predict the outcomes of genetic crosses.

11. Genetics & Probability • Probabilities predict the average outcome of a large number of events. • Probability cannot predict the precise outcome of an individual event. • In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.

12. POP Quiz! 1. Probability can be used to predict • average outcome of many events. • precise outcome of any event. • how many offspring a cross will produce. • which organisms will mate with each other.

13. That is Incorrect! • Please go back and choose the correct answer. • Think About This: If I say it will “probably” rain, does that guarantee rain? Probability cannot predict the precise outcome of an individual event.

14. That’s Correct! • GOOD JOB! • That’s right, probability can only give you an estimated answer.

15. Pop Quiz 2. Compared to 4 flips of a coin, 400 flips of the coin is • more likely to produce about 50% heads and 50% tails. • less likely to produce about 50% heads and 50% tails. • guaranteed to produce exactly 50% heads and 50% tails. • equally likely to produce about 50% heads and 50% tails.

16. That is Incorrect! • Please go back and choose the correct answer. • In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.

17. That’s Correct! • GOOD JOB! • Predictions based on probability are accurate only if a large number of events are involved.

18. Punnett Squares

19. Punnett Squares • The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett Square. • Punnett Squares can be used to predict and compare the genetic variations that will result from a cross

20. Punnett Squares • Named for Reginald Punnett(British geneticist) • Used to help solve genetics problems • Visual representation of all probable results of a genetic cross

21. POP Quiz! 3. The Punnett Square allows you to predict • only the phenotypes of the offspring from a cross. • only the genotypes of the offspring from a cross. • both the genotypes and the phenotypes from a cross. • neither the genotypes nor the phenotypes from a cross.

22. That is incorrect! • Please go back and choose the correct answer. • Hint: A Punnett Square is a visual representation of all probable results of a genetic cross.

23. That’s Correct! • GOOD JOB! • Geneticists use probability to predict the phenotypes and genotypes that MAY result from a genetic cross

24. Dominant & Recessive • A capital letter represents the Dominantallele for tall. • A lowercase letter represents the recessiveallele for short. • In this example, T = tall t = short

25. Homozygous vs. Heterozygous • Organisms that have two identical alleles for a particular trait are said to be homozygous. • Organisms that have two different alleles for the same trait are heterozygous. • Homozygous organisms are true-breeding or purebred for a particular trait. • Heterozygous organisms are hybrid for a particular trait.

26. Genotypes & Phenotypes • All of the tall plants have the same phenotype, or physical characteristics. • The tall plants do not have the same genotype, or genetic makeup. • One third of the tall plants are TT, while two thirds of the tall plants are Tt

27. Genotypes & Phenotypes • The plants have different genotypes (TT and Tt), but they have the same phenotype (tall).

28. Genotypic & Phenotypic Ratios • One fourth (1/4) of the F2 plants have two alleles for tallness (TT). • 2/4 or 1/2 have one allele for tall (T), and one for short (t). • One fourth (1/4) of the F2have two alleles for short (tt). • Genotypic Ratio is 1:2:1 • Phenotypic Ratio is 3:1

29. Genotypes & Phenotypes in Flowers • Genotype of alleles:Y= yellow seed y= green seed • All genes occur in pairs, so 2alleles affect a characteristic • Possible combinations are: • GenotypesYY Yyyy • PhenotypesYELLOW YELLOW GREEN

30. Possible Combinations

31. Genotype vs. Phenotype? 4. The physical appearance of the organism is considered the…? • Genotype • Phenotype

32. That is incorrect! • Please go back and choose the correct answer. • Hint: PHysical appearance not GENetic make-up.

33. That’s Correct! • The PHysical appearance is the PHenotype! • GOOD JOB!!

34. Punnett Square Procedure • Determine the genotypes of the parents • Write down the cross (mating) • Draw the Punnett Square • Split the letters of the genotype for each parent & put them outside the square (gametes) • Determine the possible genotypes of the offspring by filling in the Punnett Square • Summarize results (genotypes, phenotypes & ratios)

35. Let’s Try One!! • Tall stem length is dominant in garden pea plants. A heterozygous tall stem length garden pea plant’s eggs are pollinated by a heterozygous tall stem length pea plant. • You must go through all the steps in the correct order…

36. Step 1: Determine Genotype • Designate letters which will represent the genes/traits. Capital letters represent dominant traits, and lowercase letters represent recessive traits. • T = tall • t = short

37. Step 2: Write Down the Cross • Write down the genotypes (genes) of each parent. • These are often given to you or are possible to determine. • Tt x Tt

38. Step 3: Draw Punnett Square • Draw a Punnett square - 4 small squares in the shape of a window. Tt x Tt

39. Step 4: Determine Gametes • Gametes produced by each parent are shown along the top and left side of the grid/chart. • List the genes that each parent can contribute. • Females eggs across the top • Males sperm along the left side • Tt = T or t

40. Step 5: Fill in Punnett Square • Fill in each box of the Punnett Square by transferring the letter above and in front of each box into each appropriate box. • Offspring possibilities abound within the grid/chart • As a general rule, the capital letter goes first and a lowercase letter follows.

41. Steps 4 & 5

42. Step 6: Give Results • List the possible genotypes and phenotypes of the offspring for this cross. • The letters inside the boxes indicate probable genotypes (genetic makeup) of offspring resulting from the cross of these particular parents. • There are 4 boxes, and the genotypic & phenotypic results can be written either as fractions or percents.

43. Step 6: Give Results • Genotypes- TT, Tt, or tt • Phenotypes- Tall or short • Genotypic Ratio- 1:2:1 • Phenotypic Ratio- 3:1

44. Quick Review

45. POP Quiz! 5. Gametes are also known as A. Genes. B. Sex Cells. C. Alleles. D. Hybrids.

46. That is Incorrect! • Please go back and choose the correct answer. • Hint: The process of meiosis produces these.

47. That’s Correct! • GOOD JOB!! • The scientific term for sex cells is Gametes.

48. POP Quiz! 6. Two F1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall? • 100% • 50% • 0% • 25%

49. That is incorrect! • Please go back and choose the correct answer. • Hint: Organisms that have two identical alleles for a particular trait are said to be homozygous.

50. That’s Correct! • GOOD JOB! • When you cross two recessive parents the only possible outcome you can have is that recessive trait.