Understanding Gregor Mendel and His Laws of Genetics

1. Gregor Mendel “Father of Genetics” • Wrote “Experiments in Plant Hybridization” in 1865 • His work wasn’t discovered until the next century

2. Painting of Mendel

3. Mendel

4. The Chromosomal Basis of Mendel’s Laws

5. Mendel’s “principle of segregation” a. pairs of genes on homologous chromosomes separate during gamete formation (meiosis) and end up in different gametes. b. the fusion of gametes at fertilization pairs genes once again. Ex: The alleles for height in Mendel’s pea plants end up in separate gametes. Tt X Tt could yield four the offspring: TT, Tt, Tt, tt.

6. Mendel’s “principle of independent assortment” a. each pair of alleles on nonhomologous chromosomes segregates independently of other pairs during gamete formation Ex: When Mendel crossed F1 plants that were heterozygous for round yellow peas, some F2 plants did not resemble the parent plants.

7. Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants

9. Sweet Pea Flowers

10. Alleles, Alternative Versions of a Gene

11. Homozygous means having only one form of gene or allele Ex: WW or ww

12. Heterozygous means a trait represented by at least two different alleles, or forms of a gene Ex: Ww

13. Your lab or golden retriever is purebred or homozygous where as this mutt is heterozygous.

14. In the formation of a zygote, or fertilized egg, each parent of an organism contributes one form of a gene or allele, for each trait in most cases.

15. In Mendelian Genetics, dominant traits are represented by capital letters; recessive ones by lower case letters

16. Dominant traits (genes) are always expressed if the gene is present; recessive traits are expressed only if the dominant genes are absent

17. For example, widow’s peak (W) is a dominant trait in humans. If the gene for widow’s peak is present, W, the person will have widow’s Peak. (WW, Ww)

18. Speaker of the House, Paul Ryan, has widow’s peak

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

20. B sperm B B Bb haploid (n) b b diploid (2n) b meiosis II meiosis I Meiosis - eye color

21. The physical appearance of an organism is known as the phenotype; the genetic makeup (the letters) are known as the genotype Ex: Widow’s peak is the pheno- type; Ww is the genotype

23. The way to show the pos- sible pairings of genes between two organisms is called a Punnett Square.

24. Punnett Square • A Punnett square is used to show the possible combinations of gametes.

25. Monohybrid Cross • A breeding experiment that tracks the inheritance of a single trait. Dihybrid Cross • A breeding experiment that tracks • the inheritance of two traits.

26. T T t t Breed theP generation • tall (TT) vs. dwarf (tt) pea plants

27. T T produces the F1 generation Tt Tt t Tt Tt t All Tt = tall (heterozygous tall) tall (TT) vs. dwarf (tt) pea plants

28. Breed theF1 generation • Heterozygous Tall (Tt) pea plants T t T t

29. Cross a purebred black guinea pig and a purebred brown guinea pig. Black is dominant over brown.

30. B B (black) Bb Bb b All offspringare black and heterozygous. Bb Bb b (Brown)

31. If bushy eyebrows (B) are dominant over fine eyebrows, (b), show the cross between one parent heterozygous for the trait and one who is homozygous recessive.

32. What are the phenotypes and genotypes of the offspring? Answer: Bushy (Bb) 50% and fine (bb) 50%

33. Mendel’s “principle of segregation” a. pairs of genes on homologous chromosomes separate during gamete formation (meiosis) and end up in different gametes. b. the fusion of gametes at fertilization pairs genes once again. Ex: The alleles for height in Mendel’s pea plants end up in separate gametes. Tt X Tt could yield four the offspring: TT, Tt, Tt, tt.

34. Meiosis - eye color B sperm B B Bb haploid (n) b b diploid (2n) b meiosis II meiosis I

35. Mendel’s Law of Segregation

36. Mendel’s “principle of independent assortment” (2 different genes) a. each pair of alleles on nonhomologous chromosomes segregates independently of other pairs during gamete formation Ex: When Mendel crossed F1 plants that were heterozygous for round yellow peas, some F2 plants did not resemble the parent plants.

37. Independent Assortment • How many different gametes can be produced for the following allele arrangements? • Remember: 2n (n = # of heterozygotes) 1. RrYy 2. AaBbCCDd 3. MmNnOoPPQQRrssTtUu

38. Answers: 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. MmNnOoPPQQRrssTtUu: 2n = 26 = 64 gametes

40. Pleiotropy - a single gene may affect many phenotypic characters. Ex: a patient with cystic fibrosis may suffer from a lack of nutrients being absorbed from the digestive tract and chronic bronchitis

44. Epistasis – a gene at one locus alters the phenotypic expression of a gene at another locus.

46. Autosomal Inherited Traits are inherited via the autosomes (non-sex) chromosomes. How many autosomes are in each of your somatic cells?

47. That’s right! There are 44 autosomes and 2 sex chro- mosomes in each of your somatic (non-sex) cells.

48. Figure 13.x5 Human male karyotype shown by bright field G-banding of chromosomes

49. Autosomal Inherited Genetic Disorders include: • Cystic Fibrosis • Tay-Sachs Disease • Sickle Cell Anemia • Huntington Disease (this one is dominant!)

50. Testing a Fetus for Genetic Disorders