Genetics : The Science of Heredity

1. Genetics: The Science of Heredity Lesson 1 A Priest-Scientist Gregor Mendel

2. Who was Gregor Mendel? • Gregor Mendel was an Austrian monk. • He lived between 1822 to 1884. • He was a teacher & a botonist • He did experiments on hundreds of pea plants. • Why Pea Plants? • Simple genetic make up • Traits are easily observed • Can cross-pollinate or self-pollinate

3. Heredity • Father of Genetics • Mendel’s work with pea plants has become the basis of genetics, the study of heredity. • Heredity is the passing of traits from parents to offspring.

4. Mendel’s Pea Experiments • He crossed plants with two different traits, for example purple flowers with white flowers. • He started his experiments with purebred plants known as True Breeders. • Purebred plants ALWAYS produce offspring with the same trait as the parent. For example, if the parent is tall, all offspring will be tall. If the parent is short, all offspring will be short.

5. Some Pea Traits that Mendel Studied

6. F1 Generation • Mendel called the parent plants the P generation. • He called the offspring from the parents the F1 generation. • F is from the Latin word, filial, which means son. • When Mendel crossed pure pea plants with purple flowers with pure pea plants with white flowers, all the F1 generation had purple flowers. P Generation (Parent Plants) F1Generation, Offspring of the Parent Plants

7. F2 Generation • When he crossed the F1 generation peas with one another, only some of the offspring had purple flowers. These formed the F2 generation. • Mendel found that in the F2 generation, ¾ of the plants had purple flowers and ¼ of them had white flowers (3:1 ratio). F1Generation, offspring of Parent Plants F2 Generation, offspring of F1 Generation

8. Lesson 1 Review 1. Who was Gregory Mendel? 2. Why did he choose peas for his experiments? 3. What is heredity? 4. What is genetics? 5. What is a purebred plants? 6. What is the P generation? 7. What is the F1 generation? 8. What is the F2 generation?

9. Lesson 2 Understanding Mendel’s Experiments

10. Dominant and Recessive Traits • It seemed to Mendel, that for each characteristic in peas, one trait was stronger than the other. • He called the “stronger” one, the dominant trait. • He called the “hidden” one, the recessive trait. • This has become known as “Mendel’s Principle of Dominance”

11. Genes and Alleles • The traits of peas (and yours) are controlled by factors that scientists call genes. • You inherit your genes from your parents. • The different forms of a gene are calledalleles. • You inherit a combination of two alleles from your parents.

12. Dominant and Recessive Traits in Peas • For each of the 7 traits that Mendel studied in peas, there is a dominant allele and a recessive allele. • If a plant inherits both a dominant allele and a recessive allele, the dominant allele masks the recessive allele.

13. 2 alleles for white pp 2 alleles for purple PP 1 allele for purple. 1 allele for white Pp Understanding Mendel’s ExperimentsPart I

14. Understanding Mendel’s ExperimentPart II 1 allele for purple 1 allele for white Pp Pp 2 alleles for purple PP 2 alleles for white pp 1 allele for purple 1 allele for white Pp

15. Principle of Segregation • Based on the outcome of his experiment, Mendel developed his “Principle of Segregation” that states that when forming sex cells, the paired alleles separate so that each egg or sperm only carries one form of the allele. • The two forms of the allele come together again during fertilization.

16. Lesson 2 Review 16. What did Mendel find to be the same with all 7 traits of the pea plant that he studied? 17. What are genes? 18. What are dominant alleles? 19. What are recessive alleles? 20.What happens if a pea plant inherits two dominant allele of the same gene? 21. What happens if a pea plant inherits a dominant allele and a recessive allele of the same gene? 22. What happens if the pea plant inherits two recessive alleles of the same gene?

17. Lesson 3 Probability and Genetics

18. Probability • Probability is the likelihood that a particular event will occur. • The laws of probability determine what is likely to occur, not what does occur. • Mendel was the first scientist that applied the principles of probability to genetics.

19. Punnett Square • Punnett square is a table that shows all the possible combinations of alleles that can result when two organisms cross. • Using Punnett square, geneticists can predict the probabilityof occurrence of a particular trait. • The allele that each parent will pass to its offspring is based on chance, just like tossing a coin.

20. Genotypes and Phenotypes Phenotype • Genotype:Indicates the alleles that the organism has inherited regarding a particular trait. • Phenotype:The actual visible trait of the organism. Genotype

21. Homozygous and Heterozygous • Homozygous:An organism with two identical alleles for a trait (a purebred organism). • Heterozygous:An organism that has two different alleles for a trait (a hybrid organism).

22. Review 16. What it probability? How is it related to genetics? 17. What is the Punnett Square? How is it helpful to geneticist? 18. What is a genotype? 19. What is a phenotype? 20. What is a homozygous organism? 21. What is a heterozygous organism?

23. Lesson 4 • Alleles

24. Genetics • Alleles 1. Alternative forms of genes. 2. Homozygous alleles are exactly the same. 3. Dominant alleles – capitalized (TT- tall pea plants) a. Homozygous dominant 4. Recessive alleles - lowercase (tt- dwarf pea plants) a. Homozygous recessive 5. Heterozygous(different) (Tt- tall pea plants)

25. Phenotype • Outward appearance • Physical characteristics • Examples: 1. tall pea plant 2. dwarf pea plant

26. Genotype • Arrangement of genes that produces the phenotype • Example: 1. tall pea plant TT = tall (homozygous dominant) 2. dwarf pea plant tt = dwarf (homozygous recessive) 3. tall pea plant Tt = tall (heterozygous)

27. Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.

28. Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 1. What is the genotype of a homozygous tall plant?

29. Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 2. What is the genotype of a homozygous short plant?

30. Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 3. What is the genotype of a heterozygous tall plant?

31. Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 4. A plant has a genotype of Tt. What is its phenotype?

32. Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 5. A plant has a genotype of tt, what is its phenotype?

33. Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 6. What are the two alleles for the height of a pea plant?

34. Answers: 1. TT 2. tt 3. Tt 4. Tall 5. short 6. T (tall) and t (short)

35. Lesson 5Mono-Hybrid Crosses

36. Monohybrid Cross • A breeding experiment that tracks the inheritance of a single trait. • Mendel’s “principle of segregation” pairs of genes separate during gamete formation (meiosis) & reform during ferlization.

37. eye color locus B = brown eyes eye color locus b = blue eyes Paternal Maternal Homologous Chromosomes This person would have brown eyes (Bb)

38. B b male gametes B Bb x Bb b female gametes Monohybrid Cross • Example: Cross between two heterozygotesfor brown eyes (Bb) BB = brown eyes Bb = brown eyes bb = blue eyes

39. B b 1/4 = BB - brown eyed 1/2 = Bb - brown eyed 1/4 = bb - blue eyed BB Bb B Bb x Bb b Bb bb 1:2:1 genotype 3:1 phenotype Monohybrid Cross

40. Practice! Practice! Practice!!!! In cocker spaniels black (B) is dominant to red (rust) (b). 1. What would be the phenotypic ratio of a cross between a true breeding black crossed with a true-breeding rust?

41. Step 2 – List the possible gametes from each parent BB bb B B b b

42. Step 3 Draw punnett square and place the gametes on the sides. BB bb b b B B b b B B

43. Step 4 Fill in the punnett square to find the possible zygotes BB bb b b B B b b B b B b B B b B B b

44. Step 5 Determine the genotypic and Phenotypic ratios BB bb b b B B b b Phenotype B b B b B 100% Black Genotype B b B B b 100% Bb

45. Practice ProblemsComplete a Punnett Square for each of the following: T = tall plant t = short plant P = purple flowers p = white flowers • PP x pp 4. Pp x pp • Tt x TT 5. tt x TT • Pp x PP 6. Tt x tt

46. Lesson 6DihybridCross • A breeding experiment that tracks the inheritance of two traits. • Mendel’s “principle of independent assortment” a. during Metaphase I, each pair of alleles seperates independently b. formula: 2n (n = # of heterozygotes)

47. Independent Assortment • Question: How many gametes will be produced for the following allele arrangements? • Remember: 2n (n = # of heterozygotes) 1. RrYy 2. AaBbCCDd 3. MmNnOoPPQQRrssTtQq

48. Answer: 1. RrYy: 2n = 22= 4 gametes RY Ry rY ry 2. AaBbCCDd: 2n = 23= 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2n = 26= 64 gametes

49. RY Ry rY ry x RY Ry rY ry possible gametes produced Dihybrid Cross • Example: cross between round and yellow heterozygous pea seeds. R = round r = wrinkled Y = yellow y = green RrYy x RrYy

50. RY Ry rY ry RY Ry rY ry Dihybrid Cross