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
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.
Monosomy and Trisomy
How does it happen? Nondisjunction Each chrom. has two chromatids
Trisomy: Patau Syndrome 1/20,000 births severe mental retardation heart and organ defects polydactyly death by the age of one year
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. 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. Why do they rejoin?
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.)
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