1. Cytogenetics: Chromosome Mutations, Aberrations & Evolution

3. Chromosomes
Prokaryote Eukaryote

4. Eukaryotic chromosomes

7. Human karyotype

9. Why do we care?
Many diseases and birth defects are a direct result of missing, broken, or extra chromosomes.
Down Syndrome
Cri du chat Syndrome
Patau Syndrome

10. Mutations at the level of the homologous pair
EUPLOIDY: "true" ploidy, meaning two members of each homologous pair.
ANEUPLOIDY: "not true" ploidy, meaning more or fewer members than two of each homologous pair.
MONOSOMY - one homolog; partner is missing
TRISOMY - three homologs
NULLISOMY- one entire homologous pair is missing.

11. Monosomy and Trisomy

12. Down Syndrome

14. Figure: 07-04
Caption:
Incidence of Down syndrome births contrasted with maternal age.

15. How does it happen? Nondisjunction
Figure: 07-01
Caption:
Nondisjunction during the first and second meiotic divisions. In both cases, some of the gametes formed either contain two members of a specific chromosome or lack that chromosome. Following fertilization by a gamete with a normal haploid content, monosomic, disomic (normal), or trisomic zygotes are produced.
Each chrom.
has two
chromatids

16. Trisomy: Patau Syndrome
1/20,000 births
severe mental retardation
heart and organ defects
polydactyly
death by the age of one year

18. Structural Changes Deletions (deficiencies) Duplications Inversions
Translocations

19. Deletions (deficiencies)w

20. How can chromosomes break?
Ionizing radiation (production of free radicals, which act like little atomic "cannon balls", blasting through strands of DNA or c'somes.
Chemical insult.
Why do they rejoin?
Break points of chromosomes are highly reactive ("sticky"), whereas normal ends of c'somes are capped by telomeres, which do not readily bond to other molecules.

21. Breaks that occur ______ __________________ __________________ will affect both newly formed chromatids, & all daughter cells arising from them.
Breaks that occur ______ ____________________ ____________________ may affect only one chromatid. (Thereafter, only the progeny carrying the broken chromatid will be affected.)

22. Cri-du-chat Syndrome _________________ Mental retardation
Slow motor skill development
Low birth weight and slow growth
Small head (microcephaly)
Partial webbing of fingers or toes
Wide-set eyes (hypertelorism)
High-pitched cry

23. Structural Changes Deletions (deficiencies) Duplications Inversions
Translocations

24. Duplication

25. Duplications

26. Bar eye: caused by duplication

27. Duplications: source of evolutionary novelty?
Duplication is a source of new genes over evolutionary time: e.g., gene families like globins and MHC genes
______________

28. Structural Changes Deletions (deficiencies) Duplications Inversions
Translocations

29. Inversions