KEY CONCEPTS

2. KEY CONCEPTS • Definition • Revision from gr 11: • Homologous chromosomes • Paternal/maternal chromosomes • Diploid/haploid • Somatic cell/body cell

3. 1 Genetics • Genetics is the study of heredity • It deals with the similarities and differences between parents and their offspring • In Genetics we look at how characteristics are passed from one generation to the next. • Genes carry the hereditary information on chromosomes.

4. WHAT IS GENETICS JESSICA ALBA GETS MARRIED

5. Chromosomes, DNA & Genes

9. KEY CONCEPTS • Locus(i) • Alleles • Genome • Dominance & Recessiveness • Karyotype • Genotype • Phenotype • Homozygous • Heterozygous

10. 2 Genetics • Let us look at the human characteristic of having a free or attached earlobe • Click onthe attached lobe YES This ear is attached This lobe is FREE

11. 3 Genetics Attached lobe Free lobe

12. 4 Attached lobe e e • Genes occur in pairs • If we represent the gene for attached ear lobe as little “e” • Then this persons gene pair will be “ee”

13. 5 Genetic Terms ALLELE genes are partners of each other:“e” is an allele of “e” e e GENOTYPE The genes that code for a characteristic e.g. ee PHENOTYPE The characteristic expressed by the gene e.g. attached ear lobe

14. 6 Looking at the genes on Chromosomes Attached lobe Free lobe e e E E The genes occur in pairs on chromosomes The gene for free lobe is “E”

15. e e E E 7 Attached lobe Free lobe The genes occur at special positions on chromosomes called loci. One version of the gene is inherited from the father , the other from the mother If the two genes are the same e.g. ee or EE they are homozygous.

16. e E 8 There can be a mixture of attached and free ear lobe genes (Ee)- heterozygous. One gene, in this case (E) is dominant over unattached lobe (e) which is called recessive In this case the E gene completely supresses the expression of e gene so this persons will have free ear lobes

17. e e E E E 9 Summary Three possible genotypes… PHENOTYPE Free lobe Attached lobe GENOTYPE e Homozygous recessive Heterozygous dominant Homozygous dominant

18. Alleles

19. Alleles Bb

20. BL**DY IMPORTANT DEFINITIONS • The two genes on homologous chromosomes that code for the same characteristic are found on identical locations on the pair of chromosomes, called loci (singular: locus)pg 5 • Alleles are alternate forms of a gene located on the same locus of homologous chromosomes. • It seems that sometimes, one gene dominates the other of the pair. We say that the one gene is dominant,while the one that is dominated, is called the recessive gene (pg5). • A genotype Bb is called HETEROZYGOUS (or hybrid). Here the paired genes (ALLELS) for a particular trait (characteristic) are different (pg 6). • A genotype BB or bb is HOMOZYGOUS. Here the paired genes (ALLELES) for a particular trait (characteristic) ore identical (7)`

21. BL**DY IMPORTANT DEFINITIONS • The characteristics that we can see in an individual, for example, brown eyes, is known as the PHENOTYPE (pg 6). • The letters Bb indicate to us the GENOTYPE for eye colour, that is, its genetic makeup (pg 6).

23. Looking at our example of earlobes. What possible offspring can be produced if: 1 The male parent has ATTACHED lobes (ee) The female parent has FREE lobes (EE)

24. 2 Firstly we need to look at the formation of sperm cells (male gametes in the testes) to see the different types of sperm cell that can be produced from this ee parent.

25. e e e e 3 Looking at one cell in the testes dividing by meiosis Cell with double stranded chromosome pair with e-genes

26. e e e e 4 Cell divides by meiosis

27. e e e e 5 End of the first MEIOTIC division Chromosomes have separated

28. e e e e 6 Second MEIOTIC division

29. e e e e 7 End of the second MEIOTIC division – FOUR sperm cells are produced, each with a e-gene

30. e e e e e E 8 ee EE In the same way, the female will produce egg cells in the ovary. As she is EE she will only produce one type of egg cell with the E-gene In this case there is only one type of sperm cell that can be produced – all have e-gene

31. e e E E 9 ee EE The sperm and egg cells fuse to form a new child All the offspring from these parents will have a Ee genotype – They will ALL have Free ear lobes

32. Punnett Square Ee Ee Ee Ee

33. 1 Now what if both parents are heterozygous (Ee) What are the possible offspring? The male parent has ATTACHED lobes (Ee) The female parent has ATTACHED lobes (Ee)

34. e e E E 2 Looking at one cell in the testes dividing by meiosis Cell with double stranded chromosome pair with E and e genes

35. e e E E 3 Cell divides by meiosis

36. e e E E 4 End of the first MEIOTIC division Chromosomes have separated

37. e e E E 5 Second MEIOTIC division

38. e e E E 6 End of the second MEIOTIC division: FOUR sperm cells are produced, TWO with an E-gene and TWO with e-gene

39. e e E E 7 Two types of sperm cells can be produced- ONE with a e-gene and one with a E-gene

40. e e E E 8 Looking at one cell in the ovary dividing by meiosis

41. e e E E 9

42. e e E E 10

43. e e E E 11

44. e e E E 12

45. e e E E 13 Two types of egg cells can be produced- ONE with a e-gene and one with a E-gene

46. e E 14

47. e e E E 15 What possible offspring can be produced when these sperm and egg cells fuse?

48. e e e e E E E E E e E E E 16 If a E-sperm fuses with a E-egg, the child will be EE -Free Lobe If a e-sperm fuses with a E-egg, the child will be Ee -Free Lobe

49. e e e e e e e E E E E E E e e e E E E E e 17 In the same way …

50. To simplify this we use a Punnett square to show possible offspring 18 male gametes E e 3 out of 4 free lobes Ee E EE female gametes 1 out of 4 attached lobe e Ee ee Possible offspring