The life and work of Gregor Mendel

2. The life and work of Gregor Mendel

3. Over seven years, Mendel experimented on more than 28,000 pea plants! Why were his experiments so successful? • Pea plants grow quickly. • Pea plants are available in pure-breeding (homozygous) strains. • Many pea plant characteristics show discontinuous variation; they are either one form or another, with no intermediates. This means that it is easy to distinguish one trait of pea plant from another pea plant with a different trait.

4. Genetic Terminology • Trait - any characteristic that can be passed from parent to offspring • Heredity - passing of traits from parent to offspring • Genetics - study of heredity

5. Types of Genetic Crosses • Monohybrid cross - cross involving a single traite.g. flower color • Dihybrid cross - cross involving two traits e.g. flower color & plant height

6. Ways to describe Genes • Alleles - two forms of a gene (dominant & recessive) • Dominant - stronger of two genes expressed in the hybrid; represented byacapital letter (R) • Recessive - gene that shows up less often in a cross; represented by alowercase letter (r)

8. Members of the same family often look similar. Which parent do these children look more like? If the son and daughter have children of their own one day, will they also look like their parents? Why do members of the same family look similar? Humans, like all organisms, inherit characteristics from their parents. How are characteristics passed on?

9. allele for brown eyes allele for blue eyes Chromosomes in a homologous pair contain the same type of genes that code for the same characteristics, such as eye color. Each chromosome in the pair, however, may have a different version of the gene. For example, the version of a gene on one chromosome may code for browneyes, whereas the version of the gene on the other chromosome may code for blue eyes. Each different version of a gene is called an allele.

10. allele forbrown eyes allele forbrown eyes allele forblue eyes allele forblue eyes If the alleles for a characteristic in a homologous pair are the same, the organism is said to be homozygous for that characteristic. What color eyes will these homozygous pairs of alleles produce?

11. ? allele forbrown eyes allele forblue eyes If the alleles for a characteristic in a homologous pair are different, the organism is said to be heterozygous for that characteristic. What color eyes will this heterozygous pair of alleles produce? The characteristic expressed by heterozygous alleles will depend on which allele is dominant and which allele is recessive.

12. More Terminology • Genotype - gene combination for a trait(e.g. RR, Rr, rr) • Phenotype - the physical feature resulting from a genotype(e.g. red, white)

13. Genotypes • Homozygousgenotype – When the two alleles are same (2 dominant or 2 recessive genes) e.g. TT or tt; also calledpure  • Heterozygousgenotype – When the 2 alleles are different- one dominant & one recessive allele    (e.g. Tt); also calledhybrid

14. Phenotype • Phenotype • Physical characteristics

15. Genotype • Phenotype • Physical characteristics • Genotype • Genes we inherit from our parents

16. Phenotype • Facial structure Notice the similarities:

17. Phenotype • Facial structure • Eyes Notice the similarities:

18. Phenotype • Facial structure • Eyes • Smile Notice the similarities:

19. Phenotype • Facial structure • Eyes • Smile • Ears Notice the similarities:

20. Phenotype • Facial structure • Eyes • Smile • Ears • Nose Notice the similarities:

21. Phenotype • Facial structure • Eyes • Smile • Ears • Nose • Neck Notice the similarities:

22. The phenotype for a particular characteristic depends on which allele is dominant and which allele is recessive. • Dominant alleles are always expressed in a cell’s phenotype. Only one copy of the dominant allele needs to be inherited in order for it to be expressed. Dominant alleles (e.g. brown eyes) are represented by an upper case letter (e.g. ‘B’). • Recessive alleles are only expressed in a cell’s phenotype if two copies of it are present. If only one copy is present, its effect is ‘masked’ by the dominant allele. Recessivealleles (e.g. blueeyes) are represented by a lower case letter (e.g. ‘b’).

23. allele forbrown eyes allele forblue eyes The allele for brown eyes is dominant over the allele for blue eyes. So, what color will the eyes be of an individual who is heterozygous for eye color? The individual will have browneyes, because the allele for brown eyes masks the allele for blueeyes.

24. Inheritance terms

25. Genotype Phenotype homozygous dominant homozygous recessive heterozygous Mendel carried out experiments investigating just a single characteristic, which is called a monohybrid cross. There are two alleles controlling pea shape. This means there are three possible genotypes that the F2 generation of plants could inherit, leading to two possible phenotypes. SS smooth ww wrinkly Sw smooth The likelihood of a trait being produced during a monohybrid cross can be mapped out using a Punnett Square.

26. Predicting Inheritance To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes. UPPERCASE letters are used to represent dominant genes. lowercase letters are used to represent recessive genes.

27. Predicting Inheritance For example: T = represents the gene for TALL in pea plants t = represents the gene for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait! One from each parent.

28. Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two genes to the offspring or F1 generation. TT x tt T T t t

29. Punnett Square Used to help solve genetics problems

30. Punnett Squares The genes from one parent go here. The genes from the other parent go here.

31. Punnett Squares

32. Punnett Squares

33. Punnett Squares

34. Punnett Squares

35. Punnett Squares

36. Punnett Squares F1 generation

37. Interpret the Results using Probability • Likelihood that a specific event will occur • Expressed as: • Decimal, percentage, ratio, or fraction

38. Interpreting the Results The genotype for all the offspring is Tt. The genotype ratio is: Tt - 4/4 The phenotype for all the offspring is tall. The phenotype ratio is: tall - 4/4

39. Punnett Squares Your Turn!!

40. Punnett Squares F2 generation

41. Punnett Squares Next, give the genotype and phenotype ratios of the offspring (F2 generation).

42. Punnett Squares Genotype ratio: TT - 1

43. Punnett Squares Genotype ratio: TT - 1, Tt - 2

44. Punnett Squares Genotype ratio: TT - 1, Tt - 2, tt - 1

45. Punnett Squares Genotype ratio: TT - 1, Tt - 2, tt - 1 Phenotype ratio: Tall - 3

46. Punnett Squares Genotype ratio: TT - 1, Tt - 2, tt - 1 Phenotype ratio: Tall - 3, short - 1

47. Monohybrid Cross Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: RoundseedsxWrinkled seeds RRx rr (Parent P1) Genotype:Rr Phenotype:Round GenotypicRatio:100% Rr PhenotypicRatio:100% round Offspring = F1 r r Rr Rr R R Rr Rr

48. F1 Monohybrid Cross Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Roundseeds xRound seeds Rrx Rr Genotype:RR, Rr, rr Phenotype:Round & wrinkled G.Ratio:RR 25%, Rr 50%, rr 25% P.Ratio: Round 75% & wrinkled 25% R r RR Rr R r Rr rr

50. Test Crosses When an organism shows a dominant phenotype how do you know if it is homozygous or heterozygous? Mendel performed test crosses – he crossed the unknown with a plant that was homozygous recessive. If the unknown is homozygous all the F1 show the dominant phenotype. If it is heterozygous the recessive and dominant phenotype are equally expressed R R r R r r r r