1. Types of Chromosome Mutations
Refer to Figure 17-2, Griffiths et al., 2015.

2. Chromosome Mutations Deletion/ Deficiency Duplication Inversion
A B C
D E F
A C
D E F
Deletion/
Deficiency
A B C
D E F
A B B C
D E F
Duplication
A B C
D E F
A E D
C B F
Inversion
A B C
D E F
A B C
D J K
Translocation
G H I
J K
G H I
E F

3. Down Syndrome and Translocation Heterozygote
Down syndrome is caused by trisomy 21 (3 copies of chromosome 21).
95% of Down syndrome cases are associated with nondisjunction and shows no familial recurrence.
The other 5% (familial Down syndrome) is attributed to Robertsonian translocation between chromosome 21 and chromosome 14.

4. Chromatin and Gene Expression
Heterochromatin
Contains methylated histones (H3)
Associated with heterochromatin protein-1 (HP-1)
Transcriptionally Active Euchromatin
Contains hyperacetylated histones
Prevention of Heterochromatin Formation
DNA elements (barrier insulators) promote binding of histone acteyltransferase

5. Gene Silencing is Caused by the Spread of Heterochromatin
When a chromosome mutation places a gene next to heterochromatin, the gene can become inactivated.
Inversion, deletion, duplication, and translocation can place a gene next to heterochromatin.
Refer to Figure 12-25, Griffiths et al., 2015.
Heterochromatin May Spread Farther in Some Cells Than in Others

6. Position-effect Variegation
A heterozygote for a gene and a translocation can show variegated phenotype for that gene.
Position-effect variegation is exhibited by this w+/w heterozygote.
Wild-type allele is no longer wild-type in its expression in some of the eye facets.
Any chromosomal change that places a locus next to heterochromatin can result in inactivation of that gene.
A tissue or organ that is comprised of a mixture of cells that express one or the other phenotype exhibit this variegation.

7. Types of Chromosome Mutations
Refer to Figure 17-2, Griffiths et al., 2015.

8. Changes in Chromosome Number
I. Classes
A. Aberrant Euploidy
B. Aneuploidy
II. Euploidy
A. Monoploid (x): chromosome number in a basic set
B. Euploidy: multiples of monoploid number
C. Polyploid: euploid with > two sets of chromosomes
III. Examples of Polyploidy
A. Autopolyploidy : multiple chromosome sets from one species
B. Allopolyploidy: chromosome sets from different species

9. Refer to Table17-1, Griffiths et al., 2015.

10. Colchicine Induces Polyploidy
Refer to Figure 17-5, Griffiths et al., 2015.

11. Origin of the Amphidiploid Raphanobrassica
Refer to Figure 17-7, Griffiths et al., 2015.

12. Origin of Three Allopolyploid Species of Brassica
Refer to Figure 17-8, Griffiths et al., 2015.

13. Polyploidy in Animals
Parthenogenesis - development of unfertilized egg into embryo
polyploidy in leeches, flatworms, brine shrimp
polyploidy in salamanders, lizards
Polyploid frogs and toads undergo sexual reproduction.
Polyploid fish (such as salmon, trout) are not unusual.
Triploid oysters are of economic value.
In general, polyploid mammals are not viable.