Presentation on theme: "Types of Chromosome Mutations. Aneuploidy (2n +/- m) Aneuploids differ from wild-type individuals by part of a chromosome set. Nondisjunction is a common."— Presentation transcript:
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.
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
Heterochromatin Features of Constitutive Heterochromatin 1.Present at homologous sites on pairs of chromosomes 2.Always genetically inert 3.DNA sequences that are not organized into genes 4.Telomeric and centromeric regions Features of Facultative Heterochromatin 1.Referred to as silent chromatin 2.Potential to become heterochromatic (Barr body) 3.Genetic information that is not expressed once chromatin becomes condensed
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?
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.
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.