1. Chapter 8 Human Karyotypes and Chromosome Behavior Changes in chromosome number
Jones and Bartlett Publishers © 2005

2. Topics for today’s lecture
Changes in chromosome number
- sets of chromosomes
- gain or loss of individual chromosomes
- examples of aneuploidy in humans

3. Two kinds of polyploidy
Multiplication of the entire chromosome complement is called polyploidy. When all the genomes are the same, it is called autopolyploidy. When two (or more) different genomes
are duplicated, it is called allopolyploidy.

4. Formation of a tetraploid organism

5. Creation of a totally homozygous diploid cell by doubling of chromosome number in a monoploid cell by colchicine
Monoploid cells can only be grown in plants. In humans, the only viable monoploid cells are the egg and the sperm. Monoploidy in somatic cells is lethal.

6. Terms for sets of chromosomes
Monoploid = basic, standard number of chromosomes that contain one copy of each gene found in the species.
The letter X is used to designate the monoploid set.
X = Humans-23, Drosophila-4, chicken-39, cattle-30, pigeon-40, tobacco-12, Arabidopsis-5, wheat-7 pea-7, oak-12.
Dysploid = a change in monoploid number.

7. Terms for sets of chromosomes
Euploid = one or more complete sets of chromosomes.
Polyploid = three or more complete sets:
haploid (N) set
diploid = 2X N = X
triploid = 3X
tetraploid = 4X N = 2X
pentaploid = 5X
hexaploid = 6X N = 3X
duodecaploid = 12X N = 6X

8. Common mechanisms by which polyploids are naturally produced

9. Colchicine can be used to block segregation of chromosomes at anaphase results in production of polyploids.

10. Where does chromosome doubling occur?
Chromosome doubling during meiosis  Diploid gametes

11. Types of polyploids
Autopolyploids = individuals with extra copies of the monoploid set of chromosomes.
Allopolyploids = result from combinations of monoploid sets from several species.

12. Sedum suaveolens, 2n=640, x=8

13. Flow cytometry
Ploidy determinations can be made using chromosome-specific fluorescent dyes and a cell sorter.
Results need to be confirmed by classical cytogenetics.
Efficient for screening for haploids, dihaploids, etc.
Amphiploid – doubled wide hybrid.

14. KY31 tf (6x)
diploid prg
Med tf + diploid contam.
Med. tf (6x)

15. Tall fescue, 2n=6x=42 (above left)
Tall fescue, 2n=6x=42 (above left) Meadow fescue, 2n=2x=14 (above right)
Wide hybrid, 2n=8x=56 (below left) Wide hybrid, 2n=12x=84 (below right)

16. Genomic in situ hybridization

17. Where does chromosome doubling occur?
Chromosome doubling in meristematic tissue  autotetraploid clone.

18. Production of new species of Brassica
These are naturally occuring species of Brassica produced by all possible combinations of hybridizations and polyploidization

19. Gamete production by polyploids

20. This is why triploid watermelons are seedless.
Problems with being triploid  failure of chromosomes to segregate properly.
This is why triploid watermelons are seedless.

21. tetraploid by hybridization between 2 diploid species = Allotetraploid
Origins
of a fertile
tetraploid by hybridization
between 2 diploid species = Allotetraploid

22. An allopolyploid with two sequential polyploidization events
Bread wheat
An allopolyploid with two sequential polyploidization events

23. Production of New World cotton by hybridization of two species

24. Tetraploids can make 6 kinds of gametes
Tetrasomic inheritance results in many more gamete and zygote combinations.

25. Aneuploidy Aneuploidy is a gain or loss of individual chromosomes.
Normal diploids are disomic.
Trisomic = diploid with one extra chromosome (2X+1).
Monosomic = loss of a single chromosome (2X-1).

26. Aneuploidy Tetrasomic = two extra copies of one chromosome (2X + 2).
Nullisomic = individuals that have lost both copies of a particular chromosome (2X-2)
Double monosomics = ?
Double trisomics = ?

27. Capsule phenotypes for normal + 12 aneuploids
Datura stramonium
Capsule phenotypes for normal + 12 aneuploids
(in this case, a trisomic series).

28. Human aneuploidy
Humans, and animals in general, can’t tolerate much chromosome aberration.
In humans, aneuploids for X, Y, 13, 18 and 21 can survive to birth.
Trisomy 13 = Patau syndrome
Trisomy 18 = Edwards syndrome
Trisomy 21 = Down syndrome

29. Trisomy 21
Down Syndrome

30. Sex chromosome aneuploidy in humans
Syndrome Name Sex Chromosomes Frequency
Turner XO 1/2500 f
Normal females XX
Triplo-X XXX, XXXX, XXXX 1/700 b
Nullo-X Y lethal
Normal males XY
Male XYY 1/1000 m
Klinefelter XXY, XXXY, XXXXY 1/500 m

31. Kleinfelter’s Syndrome
Karyotype XXY

32. Conserved linkages (synteny groups) in cereal grasses