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

22. Females
Males
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

51. Gene Interactions Gene – piece of DNA – DNA codes for proteins
In many cases the dominant allele codes for a protein that works and the recessive allele codes for a protein that does not work

52. Incomplete Dominance
When offspring have a phenotype that is in-between the two parents
Occurs when two or more alleles influence the phenotype
Example – flowers – four o’ clocks, snapdragons
Alleles – R/R’, R/r, R/W, FR F r

54. Red
Flower

55. White
Flower

56. Pink
Flower
Red mixed with white makes pink

57. Incomplete Dominance Example #2
Incomplete dominance is a half way between point.
Halfway to dark blue is light blue.

58. Incomplete Dominance is not a blending.

59. RR rr Rr

60. Phenotypic Ratio:
1:2:1
Genotypic Ratio:
1:2:1

63. A Cross Example
Cross two pink four o clocks. Label the phenotypes.

64. More problems Cross a red four o’clock with a pink four o’clock.
Cross a red four o’clock with a white four o clock.
Cross a red eyed male fruit fly white a white eyed female fruit fly.

65. Codominace
Occurs when both alleles for a gene are expressed in a heterozygous offspring
Neither allele is dominant or recessive
Example – horse coat color

66. Horse Coat Color
Red – HR HR
White – HWHW
Roan – HR HW

67. Roan – red and white hairs

68. Blue roan - The coat has white hairs and blue hairs

69. A Cross Example
Cross two roan horses. Label the phenotypes.

70. Some more problems Cross a roan horse with a white horse.
Cross a red horse with a white horse.

71. Polygenic Inheritance
Traits controlled by two or more genes
Examples – height, skin color, coat patterns
Phenotypes are seen in a range

72. Polygenic InheritanceAB Ab aB ab
AABB
AABb
AaBB
AaBb
AAbb
Aabb
aaBB
aaBb
aabb