Chapter 6: Advanced Genetics

1. Chapter 6: Advanced Genetics

2. Chromosome and Gene Changes

3. Chromosomal change • Involves either the number of chromosomes or the arrangement of genes on a chromosome • Mutation • A change in the DNA of an organism

4. Changes Affecting the Numbers of Chromosomes

5. Genome • One single complete haploid set of an organism’s chromosomes • Haploid • one genome • Diploid • two genomes

6. Euploidy • Chromosome number is an exact multiple of the haploid number. • Polyploid = three or more genomes

7. Aneuploidy • Lack chromosomes or have extras • Do NOT have complete genomes

8. Aneuploidy • Usually caused by nondisjunction—when a chromosome pair fails to separate during meiosis • Ex: n + 1 or n - 1 • One of two things happens.

9. Normal Meiosis Metaphase Anaphase Telophase

10. Nondisjunction Metaphase Anaphase Telophase

11. Aneuploidy • Trisomy • The union of a normal gamete with one that has an extra chromosome • (n + 1) + n = 2n + 1 • Example: Down syndrome (trisomy 21)

12. Trisomy

13. Aneuploidy • Monosomy • The union of a normal gamete with one that lacks a chromosome • (n - 1) + n = 2n - 1

14. Mutations

15. Mutation • Any change in the DNA of an organism

16. Changes Within the Chromosome • Translocation • Two nonhomologous chromosomes exchange genetic information during meiosis. • Diagram, p. 134

17. A A r r B r B s s r s s C t C t D D u t u t E E v u u E v v v A A B B C C D E D r E

18. Changes Within the Chromosome • Deletion • A segment of the chromosome breaks off and is totally lost. • Diagram, page 134

19. A A A A A B B B B B C C C C C C D D D D D D E E E E E E Deletion

20. Changes Within the Chromosome • Inversion • A segment of the chromosome breaks and reattaches in the opposite orientation. • Diagram, page 135

21. A A B B D C C D C D D E E C Inversion A A B B C D E E

22. Gene Mutations • Gene mutation • The alteration of an individual gene • Point mutation • A gene mutation involving only one nucleotide

23. Gene Mutations • Substitution • A nucleotide in the DNA sequence is replaced with a different nucleotide. • Or, two nucleotides are inverted.

24. G Substitution A C C T G G C T G U G G U G C A C C G A C cysteine tryptophan threonine aspartate

25. Gene Mutations • Addition • An extra nucleotide is placed in the DNA sequence.

26. Gene Mutations • Addition • An extra nucleotide is placed in the DNA sequence. • Since a codon contains three nucleotides, this shifts all the nucleotides down by one from that point on.

27. Addition A T G C C G T A T T G A tyrosine cysteine isoleucine threonine addition A tyrosine valine histidine asparagine

28. Gene Mutations • Deletion • A nucleotide is removed from the DNA sequence. • This also shifts all the nucleotides from that point on—a frame shift.

29. Gene Mutations • Major effects • Produce no protein or very different proteins from normal • Lethal or cause severe disease

30. Gene Mutations • Minor effects • Produce a protein that is only slightly different • Little effect on the organism

31. Gene Mutations • No effect • Codon is not changed or codes for the same amino acid as the unmutated codon.

32. Biological Effects of Mutations • Lethal mutations • Result in the death of the organism

33. Biological Effects of Mutations • Mutations can happen naturally, or they can be caused by mutagens. • Mutations that happen naturally are called spontaneous mutations.

34. Biological Effects of Mutations • Mutagen • Anything that causes a mutation to occur • Chemicals, radiation, etc.

35. Biological Effects of Mutations • Somatic mutation • A mutation in a cell that does not form gametes • Germ mutation • A mutation in a cell that forms gametes

36. Biological Effects of Mutations • Somatic mutation results • No effect on the cell • Produce an odd protein • Kill the cell

37. Biological Effects of Mutations • Somatic mutation results • No effect on the cell • Produce an odd protein • Kill the cell • No significant effect in a multicellular organism

38. Biological Effects of Mutations • Germ mutation results • May be lethal to the gamete • Affects cells in the next generation—produce gametes with some genetic change

39. Biological Effects of Mutations • Germ mutation results • Genetic screen • An inborn mechanism that prevents individuals with severe genetic diseases from either living or reproducing

40. Gene Expression

41. Gene expression • The activation of a gene that results in its transcription and the production of a specific protein • Cellular differentiation • The specialization of cells; the process whereby a cell becomes a specific type of cell

42. Gene expression can be controlled by molecular factors and by environmental factors. • Molecular factors • Control of transcription • Control of translation • Control by hormones

43. Gene Expression and Cancer • Cancer • Unrestrained cell growth that has escaped the normal controls of the cell cycle • Tumor • An abnormal mass of cells produced by abnormal cell division

44. Gene Expression and Cancer • Benign • Cancer cells that stay within the tumor and do not spread to other parts of the body • Malignant • Cancers that invade surrounding tissues and may spread (metastasize)

45. Gene Expression and Cancer • Carcinogen • A substance that increases the risk of cancer • Certain chemicals, viruses, radiation, etc.

46. Gene Expression and Cancer Genes called proto-oncogenes and tumor suppressor genes are responsible for regulating the cell cycle.

47. Gene Expression and Cancer • Proto-oncogenes • Code for proteins that stimulate cell division or affect the synthesis of growth factors • Promote cell growth

48. Gene Expression and Cancer • Tumor suppressor genes • Code for proteins that prevent uncontrolled cell growth

49. Gene Expression and Cancer Mutations that inactivate tumor suppressor genes or overactivate proto-oncogenes can increase the likelihood of cancer.

50. Gene Expression and Cancer • Mutated proto-oncogenes are called oncogenes. • Oncogenes cause cells to divide uncontrollably. • This can lead to the growth of a tumor.