Understanding Chromosome Theory of Heredity for Gene Mutations

1. Chapter 10

2. 10.1 The Chromosome Theory of Heredity • Chromosomes are located in the nucleus • Factors (genes) are found on chromosomes • Sutton discovered that genes are on chromosomes in 1902

3. Chromosome Theory of Heredity • States that genes are located on chromosomes and each gene occupies a specific place on a chromosome • Only one allele is on a chromosome

6. Independent Assortment

7. Gene Linkage • Genes on a chromosome are linked together • Inherited together – THEREFORE they do not undergo independent assortment

8. Linked Genes- genes on the same chromosome – inherited as a package Height Gene A Flower color gene B Flower position gene C

9. Linkage Groups • Package of genes that are always inherited together • Chromosome • One linkage group for each homologous pair

10. When they are lined up they can become twisted and switch genes Crossing Over

11. So you could then have ….. G G g g W w W w switch

12. Recombinants – individuals with new combinations of genes • Crossing Over – gives rise to new combinations – Prophase I

13. Sex Linkage • Stevens – made observations of meal worm chromosomes

14. Sex Chromosomes • One pair • Female – XX • Male – XY

15. Autosomes • All the chromosomes except the sex chromosomes

16. Sex Determination

18. Genes on Sex Chromosomes • Sex chromosomes determine a person’s sex • Sex chromosomes also contain genes

19. Sex Linked • A gene located on a sex chromosome • Usually X • Example – Fruit Fly Eye Color • So the gene for eye color is on the X chromosome and not the Y

21. Fruit Fly Sex Chromosomes X X X Y

22. Males Females XRY XrY XRXR XRXr XrXr Red Eyed White Eyed

24. Mutations

25. A change in the DNA of an organism • Can involve an entire chromosome or a single DNA nucleotide and they may take place in any cell

26. Germ Cell Mutation • Occur in an organism’s germ cells (gametes)- can only affect offpsring

27. Somatic Mutations • Take place in an organisms body cells and can affect the organism

28. Lethal Mutation • Cause death, often before birth

29. Good Mutations • Some mutations can be beneficial – these organisms have a better chance to reproduce and therefore have an evolutionary advantage • Provide the variation on which natural selection acts

30. Chromosome Mutations

31. Are either changes in the structure of a chromosome or the loss of an entire chromosome or an addition • Four Types (duplication, deletion, inversion and translocation)

32. Duplication – segment of a chromosome is repeated • Deletion – the loss of a chromosome or part due to chromosomal breakage – that information is lost

33. Inversion – a chromosomal segment breaks off and then reattached in reverse orientation to the same chromosome

34. Translocation – a chromosome breaks off and reattaches to another non-homologous chromosome

36. Nondisjunction • Some chromosome mutations alter the number of chromosomes found in a cell • Nondisjunction – the failure of a chromosome to separate from its homologue during meiosis

38. Gene Mutations

39. May involve large segments of DNA or a single nucleotide within a codon • Involve individual genes

40. Point Mutations – 3 types • The substitution, addition or removal of a single nucleotide

41. Substitution – a point mutation where one nucleotide in a codon is replaced with a different nucleotide, resulting in a new codon Ex. Sickle Cell Anemia – sub. Of A for T in a single codon

42. 2 & 3. Insertion and Deletions – one or more nucleotides is lost or added – have more serious effects

43. Frameshift Mutation • When a nucleotide is lost or added so that the remaining codons are grouped incorrectly • Insertions and deletions are frameshift mutations

44. THE FAT CAT ATE THE RAT

49. Polyploidy • Condition in which an organism has an extra set of chromosomes • 3N, 4N • Usually fatal in animals • Plants – usually more robust • Caused by - Nondisjunction

50. 10-3 Regulation of Gene Expression • As biologists have intensified their studies of gene activity, it has become clear that interactions between different genes and between genes and their environment are critically important