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

2. Aneuploidy (2n +/- m)
Aneuploids differ from wild-type individuals by part of a chromosome set.
Nondisjunction is a common mechanism for aneuploidy.
Aneuploidy can be the cause of disorders such as Down Syndrome.

3. Examples of Aneuploidy
Nullisomy (2n -2)
Usually lethal in diploids
Tolerated in some polyploids
Monosomy (2n - 1)
Gene imbalance results (missing chromosome)
Expression of genes on lone chromosome (hemizygosity)
Trisomy (2n + 1)
Gene imbalance results (extra chromosome)
Viability depends on chromosome and species
Disomy (n + 1)
Phenomenon in haploid organisms

4. Meiotic Nondisjunction Generates Aneuploid Products
Refer to Figure 17-12, Griffiths et al., 2015.

5. Examples of Aneuploidy
Sex Chromosomes (Human X and Y)
XO : Turner Syndrome
XXY: Klinefelter Syndrome
XXX: Triplo-X Syndrome
XYY: XYY Syndrome
Autosomes
Trisomy 13: Patau Syndrome
Trisomy 18: Edward’s Syndrome
Trisomy 21: Down Syndrome

7. Heterochromatin Features of Constitutive Heterochromatin
Present at homologous sites on pairs of chromosomes
Always genetically inert
DNA sequences that are not organized into genes
4. Telomeric and centromeric regions
Features of Facultative Heterochromatin
Referred to as silent chromatin
Potential to become heterochromatic (Barr body)
3. Genetic information that is not expressed once chromatin becomes condensed

8. Mammalian X Chromosome Inactivation
Calico cats are usually females heterozygous for orange allele and black allele at an X-linked locus.
Male calico cats are very rare. Why is this the case?

9. X Chromosome Inactivation
Most genes on the inactivated X chromosome are silenced (turned off, not expressed).
Genes on the inactivated X chromosome remain silenced in descendant cells.
Heritable alteration of this type is an example of epigenetic inheritance.
Chromosomal DNA sequence remains unchanged.

10. Mammalian X Chromosome Inactivation
Inactivated X chromosome becomes highly condensed, darkly staining structure called Barr body. State of inactivation is transmitted down the cell lineage.

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

12. The fates of a million implanted human zygotes
50% of spontaneous abortions are associated with chromosome abnormalities.
Over half of these are trisomics, with trisomy 21 accounting for 9% of them.
18% of abnormalities are the Turner condition.
~ 0.6% of birthed infants have chromosome abnormalities.
~ 36% of birthed infants with chromosome abnormalities are aneuploidy of sex chromosome.
~ 23% of birthed infants with chromosome abnormalities are trisomics.
Refer to Figure 17-37, Griffiths et al., 2015.

13. Relationship between Genotype and Phenotype
Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
amino acid
sequence
protein
function
phenotype
organism