1. Patterns of inheritance:
Mendel and beyond

3. Contrasting characters in peas

4. Experiment with garden peas I

5. In this case a true-breeding tall plant was crossed with a true-breeding short plant. All of the plants in the next generation were tall.

6. These are the results Mendel obtained when he crossed two heterozygotes.

7. ‘Paint-pot’ theory of inheritance

8. Mendel’s finding was contrary to the prediction of the ‘Paint-pot’ theory of inheritance

9. Mendel’s 1st law- law of segregation

10. Mendel’s law of segregation -explanation of monohybrid ratio

11. Mendel described patterns of inheritance in the 1860s, but it wasn’t until the early 1900s that inherited traits, genes, were linked to cellular structures called chromosomes. The number of chromosomes varies among species, but all chromosomes contain genes arranged linearly at specific locations, called loci.

12. This is how geneticists today represent the cross from the previous screen. The original plants are the P generation and their offspring are the F1 generation. The T and t symbols represent dominant and recessive alleles of a single gene.

13. we breed the offspring to one another in the cross Tt x Tt, and wish to predict the results we need to follow the production of gametes during meiosis. These individuals make gametes with either T or t in equal numbers.

14. The chance of gametes of different types encountering one another is represented on a Punnett square. The genotypic ratio of homozygous dominant: heterozygous: homozygous recessive individuals is 1:2:1.

15. Many genetics problems will fall in the category of a monohybrid cross
Many genetics problems will fall in the category of a monohybrid cross. They all can be approached using the model above

16. Testcross. a heterozygote was crossed with a homozygous recessive individual. A situation in which an individual of dominant phenotype, but of unknown genotype, is crossed with one or more recessive individuals. This can provide information on the unknown genotype.

17. Dihybrid cross

18. Dihybrid cross

19. Dihybrid cross
The inheritance of two contrasting characters were considered at the same time

20. Law of independent assortment

21. Mendel’s 2nd law

22. Mendel’s 2nd law explained by observing movement of chromosomes at meiosis

23. Cell division

24. The cell cycle

25. Interphase

26. Interphase

27. Mitosis – division of the nucleus

28. Prophase metaphase anaphase telophase
Division of the nucleus
Prophase metaphase anaphase telophase

29. Division of the cytoplasm

30. Produce identical daughter cells

31. Mitosis and cell cycle

32. Meiosis
Reduction division
Generate variability in gametes

33. Meiosis-Interphase

34. Meiosis-prophase I

35. Meiosis-metaphase I

36. Meiosis-anaphase I

37. Meiosis-telophase I

38. Meiosis I -animated

39. Meiosis II
prophase II
metaphase II
anaphase II
telophase II

40. Meiosis II -animated

41. Meiosis-overall

42. Independent assortment

43. Crossing over

44. Anaphase I and II note new gene combinations as a result of crossing over

45. Comparing Mitosis and Meiosis

46. Comparing Mitosis and Meiosis

47. Incomplete dominance
In some cases, alleles may not interact in a dominant/recessive pattern. Heterozygotes have an intermediate phenotype or express both alleles. The genotypic ratio will match the phenotypic ratio. Snapdragons demonstrate incomplete dominance.

48. Incomplete dominance II

49. Multiple allele

50. Linkage and crossing-over

51. Recombinant frequency

52. Skin colour_a pair of twin sisters

53. Continuous or discontinuous

54. Polygenic effects on genetic variation

55. Polygenic inheritance_skin colour

56. Skin colour is a continuous variation because…

57. How would U explain the very different skin colour of the twin sisters?

58. X-inactivation

59. X-inactivation