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. Chromosome theory of inheritance: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. Thomas Hunt Morgan
Studied fruit flies – Drosophilia melanogaster

11. Fruit Flies are excellent for genetic studies because:
Reproduce quickly
Easy to raise
Many mutations
Have 8 chromosomes (n=4)

13. Fruit Fly Mutations
                  
            

14. Thomas Hunt Morgan began to carry out experiments with

15. Morgan looked at TWO traits
Gray bodies – G
Normal Wings - W
Black bodies – g
Small wings – w

16. The flies mated….

17. The female laid eggs
                                                  

18. GGWW
ggww P1 x F1
GgWw
100%

19. Morgan then mated the F1 back to the recessive parent
GgWw x ggww
Expected ratio – 1:1:1:1
25% GgWw % Ggww
25% ggWw % ggww

20. Morgan’s Actual Results
41.5% gray normal
41.5% black small
8.5 % black normal
8.5% gray small

21. Conclusion
Gene for body size and wing color were somehow connected or linked
Can’t undergo independent assortment

22. Linkage Groups Package of genes that are always inherited together
Chromosome
One linkage group for each homologous pair
Fruit flies – 4 linkage groups
Humans – 23 linkage groups
Corn – 10 linkage groups

23. So linkage groups explain the high percentages (41.5%) but
What about the 8.5%??????

24. The combinations that were expected would be:
17% had new combinations
The combinations that were expected would be:
Gray normal – GW or
Black small - gw

25. P1 G G g g W W w w
Dad
Mom

26. F1 G g W w

27. g G g g W w w w F1 F1 F1 X
Recessive
Fruit Fly
Heterozygous

28. The Offspring of the Cross
and W w w w F1 F1
41.5 %
41.5 %

29. Genes of the Heterozygous ParentW W w w
The homologous pair copied

30. The homolgous pairs pair up in Prophase and form a tetradW W w w

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

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

33. The other offspring of the cross
and w w W w F1 F1
8.5 %
8.5 %

34. The 17% that had new combinations are known as
Recombinants – individuals with new combinations of genes
Crossing Over – gives rise to new combinations – Prophase I

35. Gene Mapping Sturtevant – associate of Morgan
Crossing over occurs at random
The distance between two genes determines how often they cross over
Genes that are close do not crossover often
Genes that are far apart – cross over often

36. So……
If you know the frequency with which crossing over occurs then you can use that to map the position of the genes on the chromosome

38. Frequency of crossover exchange...
                       
   is GREATER the FARTHER apart 2 genes are    is proportional to relative distance                                       between 2 linked genes    Relative distance is established as...        1% crossover frequency =                                   1 map unit of map distance        1%   CrossOver  Freq   =    1   centiMorgan

39. Sex Chromosomes
One pair
Female – XX
Male – XY
        
        

40. Sex Linkage
Stevens – made observations of meal worm chromosomes

41. Autosomes
All the chromosomes except the sex chromosomes

42. Sex Determination

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

45. Sex Linked genes 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

46. Sex linked genes
Male pattern baldness
Hemophelia
colorblindness

48. Fruit Fly Sex Chromosomes

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

51. Mutations

52. 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

53. Germ Cell Mutation
Occur in an organism’s germ cells (gametes)- can only affect offspring

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

55. Lethal Mutation
Cause death, often before birth

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

57. Chromosome Mutations

58. 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)

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

60. Inversion – a chromosomal segment breaks off and then reattached in reverse orientation to the same chromosome
Translocation – a chromosome breaks off and reattaches to another nonhomologous chromosome

62. 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

64. Gene Mutations

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

66. Point Mutations – 3 types
The substitution, addition or removal of a single nucleotide
Substitution – a point mutation where one nucleotide in a codon is replaced with a different nucloetide, resulting in a new codon
Ex. Sickle Cell Anemia – sub. Of A for T in a single codon

67. 2 & 3. Insertion and Deletions – one or more nucleotides is lost or added – have more serious effects

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

69. THE FAT CAT ATE THE RAT

70. 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

71. 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

72. 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

73. 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

75. Red
Flower

76. White
Flower

77. Pink
Flower
Red mixed with white makes pink

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

79. Incomplete Dominance is not a blending.

80. RR rr Rr

81. Phenotypic Ratio:
1:2:1
Genotypic Ratio:
1:2:1

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

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

86. Roan – red and white hairs

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

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

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