1. Chapter 17 Large-Scale Chromosomal Changes
Changes in Chromosome Number
Changes in Chromosome Shape

2. Types of chromosome mutations
all generated by natural mutagens—extreme temps, UV, chemicals, etc.

3. Euploidy
euploidy: change of chromosome number involving 1 or more whole genomes
autopolyploidy = doubling of genome from “wild type” (e.g., tetraploid from diploid, hexaploid from triploid)
allopolyploid = doubling of genome from hybrid of two distinct taxa (e.g., varieties, species, genera)

4. Examples of ploidy levels
Balanced (normal meiosis)
2n = diploid
4n = tetraploid
6n = hexaploid
8n = octoploid
and so on
Unbalanced (abnormal meiosis)
1n = monoploid
3n = triploid
5n = pentaploid
7n = heptaploid
[usually hybrids of ploidy levels on left]

5. Facts about polyploidy and allopolyploids
Uncommon in animals but abundant (ancient and ancestral?) in plants
Recent genetic research shows allopolyploids far more common than autopolyploids—different from theory
Many allopolyploids found with multiple origins—contrary to evolutionary paradigm of “single origin” for species

6. Polyploids often produce larger structures, e. g
Polyploids often produce larger structures, e.g., guard cells, pollen,...

7. ...and fruits (e.g., tetraploid grapes)

8. Meiotic pairing in triploids—> unbalanced gametes (sterility)
Mules have 63 chromosomes, a mixture of the horse's 64 and the donkey's 62. The different structure and number prevents the chromosomes from pairing up properly and creating successful embryos, rendering mules infertile.

9. Colchicine used to induce polyploidy

10. A famous natural allohexaploid: Bread wheat (Triticum aestivum)

11. Famous Examples of Allopolyploid Complexes
Appalachian Asplenium ferns—several diploids, triploid hybrids, several tetraploids
Domesticated coffee (Coffea arabica)--parentage documented through molecular cytogenetic “chromosome painting”
Dandelions, roses, blackberries--more complicated groups that also do agamospermy (sex without seeds)

12. Evolutionary consequences of polyploidy
polyploids often more physiologically “fit” than diploids in extreme environments
polyploids reproductively isolated from original ploidy levels, may eventually differentiate
allopolyploids commonly occupy ecological niches not accessible to parental types
opportunities for gene silencing or chromosomal restructuring without disastrous consequences

13. Monoploid plants grown in tissue culture

14. Summary polyploids common in plants
autoploids formed by doubling of “wild type” genome, allopolyploids from doubling of hybrid
allopolyploids far more common than autopolyploids
polyploids often more “fit” than parent(s), often in niches different from parent(s)
opportunities for evolutionary change through gene silencing or chromosome restructuring

15. Facts about aneuploids
Rare in animals, always associated with developmental anomalies (if they survive)
Most well known examples in human genetic diseases
Common in plants, sometimes show phenotypes, sometimes not

16. Extra chromosome 21 Down Syndrome

18. Meiotic nondisjunction = aneuploid products
Figure step 1

19. Meiotic nondisjunction = aneuploid products
Figure step 2

20. Meiotic nondisjunction = aneuploid products
Figure step 3

21. Meiotic nondisjunction = aneuploid products
Figure step 4

22. Meiotic nondisjunction = aneuploid products
Figure step 5

23. Meiotic nondisjunction = aneuploid products
Figure step 6

24. Trisomics of Datura (jimsonweed)

25. Large-Scale Chromosomal Changes Changes in Chromosome Structure

26. Types of chromosome mutations

27. Deletion loops in Drosophila
genes missing
from chromosome #2 #1 #2

28. Deletion loops in Drosophila

29. Deletion origin of “cri du chat” syndrome see hear: http://www.youtube.com/watch?v=TYQrzFABQHQ

30. Duplications following polyploidy in Saccharomyces

31. Inversions cause diverse changes
breakpoints
between genes
1 breakpoint
between genes,
1 within gene
breakpoints
within 2 genes

32. Inversion loops at meiosis

33. Paracentric inversions can lead to deletion products

34. Paracentric inversions can lead to deletion products

35. Paracentric inversions can lead to deletion products

36. Paracentric inversions can lead to deletion products

37. Paracentric inversions can lead to deletion products

38. Paracentric inversions can lead to deletion products

39. Pericentric inversions can lead to duplication-and-deletion products
Figure step 1

40. Pericentric inversions can lead to duplication-and-deletion products
Figure step 2

41. Pericentric inversions can lead to duplication-and-deletion products
Figure step 3

42. Pericentric inversions can lead to duplication-and-deletion products
Figure step 4

43. Reciprocal translocation revealed by molecular cytogenetics

44. Chromosome segregation in reciprocal-translocation heterozygote
Figure step 1

45. Chromosome segregation in reciprocal-translocation heterozygote
Figure step 2

46. Chromosome segregation in reciprocal-translocation heterozygote
Figure step 3

47. Variegation resulting from gene’s proximity to heterochromatin

48. Variegation in translocation heterozygote

49. Chloroplast rearrangements
Great evolutionary significance in reconstructing relationships among land plant lineages
Can easily be screened for by PCR amplification of “universal” chloroplast gene primer pairs flanking large regions of chloroplast
Judd et al. (2002)

50. Chloroplast rearrangements
Major inversions found in certain groups of families of bryophytes, pteridophytes, gymnosperms and several groups of angiosperms
Loss of one copy of inverted repeat in a few families!
Numerous losses of certain introns across angiosperms (e.g., rpl2 in Cactaceae)
Differences in size of large single-copy region by expansion or contraction of intergenic spacers

51. Summary
each different chromosomal change shows characteristic meiotic pairing as a “signature”
deletions in diploids often have grave consequences; in polyploids do not but may lead to differentiation of new organisms
duplications (in plants) generally have few or no consequences, often provide additional genes for evolutionary processes to act on (silencing, co-option by different functions)