Cytogenetics

1. Cytogenetics Study of Changes in Chromosome Number or Structure Field Horsetail 1

2. Human Chromosomes 22 pairs of autosomes, one pair of sex chromosomes (X & Y) 2

3. Genetic Testing DNA analysis Biochemical tests Chromosome analysis Chorionic villus sampling Amniocentesis 3

4. Karyotype Analysis Actively growing cells: white blood cells, tissue biopsy amniotic fluid, chorionic villi Cultured in vitro: mitotic cells arrested in metaphase colcemid, colchicine Fix cells on slide: hypotonic swelling, methanol/acetic acid, spread Stain to visualize: banding patterns, size, centromere Capture image: digital image Prepare karyotype: arrange chromosomes by size, shape, cen, banding patterns 4

5. Human Male Karyotype G-banding Ideogram 5

6. Chromosome Descriptions Centromere position: 6

7. Chromosome Descriptions Position of gene locus: p arm p13 q arm q41 7

8. Chromosome Abnormalities per 100,000 Pregnancies Abort Live 15% (10-25%) of recognized pregnancies abort spontaneously 8

9. Changes in Chromosome Number Ploidy - # of chromosome sets Monoploid - basic set = n Ex. humans, n = 23 haploid = 1n = 23 diploid = 2n = 46 Polyploid - multiple (>2 sets) Triploid (3n), Tetraploid (4 n), Hexaploid (6) 9

10. Changes in Chromosome Number Endoreduplication can lead to instant evolution Only a few animals tolerate polyploidy Ex. salamanders, fish, frogs, lizards, chickens Ex. salivary glands, myocardial cells Polyploid humans 10

11. Changes in Chromosome Number Polyploidy - Common in plants Karpechenko (1928) crossed radish with cabbage X 11

12. Changes in Chromosome Number Polyploidy - larger commercial plants AutopolyploidyAllopolyploidy amphidiploid or allotetraploid 12

13. Changes in Chromosome Number Origin of Amphidiploid (Allotetraploid) No homologous chromosomes pair No meiosis 13

14. Aneuploidy - Gain or Loss of 1 or 2 Chromosomes Results from Nondisjunction 14

15. Aneuploidy - Gain or Loss of 1 or 2 Chromosomes 15

16. Aneuploidy - Gain or Loss of 1 or 2 Chromosomes Hypoploidy - missing chromosomes Autosomal monosomics - undetected pregnancy Hyperploid - extra chromosomes 16

17. Aneuploidy - Gain or Loss of 1 or 2 Chromosomes Previously covered 17

18. Autosomal Trisomy Trisomy 21 - Down syndrome, 2n + 1 = 47, 1 in 700 live births Mental retardation, skin folds (epicanthic) corner of eyes, Skull wide, flattened at back, iris spots, protruding tongue 18

19. Autosomal Trisomy Trisomy 18 - Edwards syndrome, 2n + 1 = 47, 2.5 in 10,000 live births Small, slow growth, low set malformed ears, malformed feet, mental retardation. Most die of heart problems within 6 months. Characteristic fist clenching, rocker feet 19

20. Autosomal Trisomy Trisomy 13 - Patau syndrome, 2n + 1 = 47, 1 in 15,000 live births Cleft lip and palate common, small eyes, polydactyly, heart, brain, nerve defects, mental & developmental retardation Most die within 3 months 20

21. Somatic Aneuploids Result from nondisjunction during development (mitosis) Mosaics Ex. XY/XXY Partial Klinefelter syndrome XO/XYY Gynandromorph, split sex X X w w+ m m+ XO X X X w w w+ w+ m m m+m+ 21

22. Chimeras Two embryos fuse - one individual with two genotypes Chances increase with in vitro fertilization Female/Male - hermaphrodite Sperm, blood, hair - distinct DNA profiles 22

23. Changes in Chromosome Structure Summary of Chromosome Rearrangements 23

24. Deletion - del -  Many genes may be lost 24

25. Deletion - del -  Cri-du-chat syndrome - deletion 5p severe mental retardation, numerous physical abnormalities 25

26. Duplication Arise through replication slippage or unequal crossing over 26

27. Duplication Arrangements of duplicate genes 27

28. Duplication Duplicate genes - can be important in evolution Multigene families Ex. hemoglobin genes clustered Different ones expressed in embryo, fetus, and adult 28

29. Duplication Region 16A duplication - Bar eyes in Drosophila 29

30. Duplications Trinucleotide repeat expansion – (CCGn) Ex. Fragile X - mental retardation 30

31. Inversions Breakage and rejoining of chromosome segments Paracentric Pericentric 31

32. Consequences of Paracentric Inversions Loop forms to Align genes Crossover within inversion loop leads to Acentric and Dicentric fragments 32

33. Consequences of Paracentric Inversions Breakage occurs during Anaphase Results in gene loss Lethal CO suppression 33

34. Consequences of Pericentric Inversions CO in inversion loop results in Deletions Duplications 34

35. Translocations Exchange between nonhomologous chromosomal regions Nonreciprocal Reciprocal Balanced – correct number of genes, rearranged 35

36. Consequences of Translocations Reciprocal Translocation Heterozygote Duplications Deletions 36

37. Consequences of Translocations Familial Down Syndrome Translocation Carrier One possible outcome 37

38. Consequences of Translocations Familial Down Syndrome Translocation Carrier Second possible outcome 38

39. Consequences of Translocations Familial Down Syndrome Translocation Carrier Third possible outcome 39

40. Consequences of Translocations Cri-du-chat syndrome – due to translocation in parent 40

41. Consequences of Translocations Chronic myelogenous leukemia – uncontrolled replication myeloblasts Philadelphia chromosome – translocation 22 & 9 ABL protooncogene from 9 fuses with BCR on 22. Fusion protein stimulates cell growth. 41

42. Robertsonian Translocations Fusion of chromosomes at centromeres – important in evolution Rodents Chimpanzee Human telocentrics none 42

43. Detection of Translocations FISH - chromosome painting – reciprocal exchange 43