1. PowerLecture: Chapter 12
Chromosomes and Human Inheritance

2. Philadelphia Chromosome
1st abnormal chromosome associated with a cancer
Causes chronic myelogenous leukemia (CML)

3. Sex Chromosomes Discovered in late 1800s Mammals, fruit flies
XX is female, XY is male
In some other groups XX is male, XY female
Human X and Y act homologues

4. Karyotype Preparation
Fig. 12-3a-e, p.189

5. Karyotype Diagram
Fig. 12-3f, p.189

6. Karyotype Preparation
Fig. 12-4, p.189

7. Autosomal Dominant Inheritance
Trait typically appears in every generation
Fig a, p. 190

8. Autosomal Dominant Inheritance example… Achondro-plasia
Fig. 12-5, p.190

9. Achondroplasia Autosomal dominant allele
Homozygous usually leads to stillbirth
Heterozygotes display a type of dwarfism
(short arms and legs relative to other body parts)

10. Huntington Disorder Autosomal dominant allele
Causes involuntary movements, nervous system deterioration, death
Symptoms appear after age 30
People often pass allele on before they know they have it

11. Autosomal Recessive Inheritance Patterns
If parents are both heterozygous, child will have a 25% chance of being affected
Fig b, p. 191

12. Galactosemia Caused by autosomal recessive allele
Gene specifies a mutant enzyme in the pathway that breaks down lactose
lactose
galactose
enzyme 1
+ glucose
galactose-1-
phosphate
enzyme 2
galactose-1-
phosphate
enzyme 3
intermediate
in glycolysis

13. Hutchinson-Gilford Progeria
Mutation causes accelerated aging
No evidence of it running in families
Appears to be dominant
Seems to arise as spontaneous mutation
Usually causes death in early teens

14. The Y Chromosome Fewer than two dozen genes identified
SRY gene (sex-determining region of Y) is the master gene for male sex determination

15. The X Chromosome Carries more than 2,300 genes
Most for nonsexual traits
Genes on X chromosome can be expressed in both sexes

16. Sex Determination diploid germ cells in female diploid germ cells
in male
meiosis, gamete
formation in both
female and male:
eggs
sperm X x Y X X
Fertilization: X X X XX XX
sex chromosome
combinations
possible in new
individual XY XY X
Fig. 12-8a, p.192

17. Thomas Morgan Worked with fruit flies
Reciprocal crosses - 2 crosses where the trait of each sex is reversed
Example -
1- White eyed male X Red eyed female
2- White eyed Female X Red eyed male

18. White-eyed males show up in F2
Thomas Morgan X X
1/2 Y Y
recessive male
all red-
eyed F1
offspring
1/2
1/4 X X
1/4
1/4 X X
1/2
1/4 X X
homozygous
dominant
female
1/2
gametes
White-eyed males show up in F2
generation
Fig. 12-9, p.193

19. Examples of X-Linked Traits
Red-Green Color blindness
Hemophilia A
Duchenne Muscular Dystrophy

20. Hemophilia
Fig , p.194

21. Duplication Gene sequence repeated several to hundreds of times
Can occur through unequal crossing over
Can be found in normal chromosomes
May have adaptive advantage
Useful mutations may occur in copy

22. Duplication
normal chromosome
one segment
repeated
three repeats

23. Deletion Loss of some segment of a chromosome
Most are lethal or cause serious disorder

24. Deletion
Cri-du-chat
Fig , p.196

25. Inversion Section of DNA is reversed Usually not a problem for carrier
May cause problems in meiosis
segments
G, H, I become inverted
In-text figure Page 196

26. Translocation
A piece of one chromosome becomes attached to a nonhomologous chromosome
Most are reciprocal
Example - Philadelphia chromosome

27. Translocation one chromosome In-text figure Page 206 a nonhomologous
nonreciprocal translocation
In-text figure Page 196

28. Duplications & Translocations
Karyotype comparing gibbon chromosomes to human chromosome regions.
Fig , p.197

29. Chromosome Structure
Alterations to chromosome structure are usually bad
Duplications are adaptive: one gene functions normally - the other is free to mutate
Chromosome structure evolves

30. Chromosome Structure Human n=23
Chimpanzees, gorilla, or orangutan n=24
During human evolution, two chromosomes fused to form chromosome #2

31. Chromosome Structure human chimpanzee gorilla orangutan
Fig , p.197

32. Aneuploidy Individuals have one extra or less chromosome
(2n + 1 or 2n - 1)
Major cause of human reproductive failure

33. Polyploidy
Individuals have three or more of each type of chromosome (3n, 4n)
Common in flowering plants
Lethal for humans

34. Nondisjunction n + 1 n + 1 n - 1 n - 1
chromosome alignments at metaphase I
NONDISJUNCTION AT ANAPHASE I
alignments at metaphase II
anaphase II
CHROMOSOME
NUMBER IN
GAMETES
Fig b, p.198

35. Nondisjunction
Fig a, p.198

36. Nondisjunction Down Syndrome - Trisomy 21
Risk of Down syndrome increases dramatically in mothers over age 35

37. Down Syndrome
Fig , p.199

38. Nondisjunction Turner Syndrome- Monosomy X (XO)
Klinefelter Syndrome- XXY
XYY

39. Fig b,p.200

40. Phenotypic Treatments
Symptoms of many genetic disorders can be minimized or suppressed by
Dietary controls
Adjustments to environmental conditions
Surgery or hormonal treatments

41. Genetic Screening
Large-scale screening programs detect affected persons
Newborns in United States routinely tested for PKU
Early detection allows dietary intervention and prevents brain impairment

42. Preimplantation Diagnosis
in-vitro fertilization
At the 8 cell stage 1 cell is removed and its genes analyzed
If cell has no defects, the embryo is implanted