mutations at the level of the homologous pair euploidy: "true" ploidy, meaning two members of each...

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  • 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.
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  • Trisomy: Patau Syndrome 1/20,000 births severe mental retardation heart and organ defects polydactyly death by the age of one year
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  • 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.
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  • 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.
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  • Structural Changes Deletions (deficiencies) Duplications Inversions Translocations
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  • 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
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  • Turner Syndrome Clinical features
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  • Possible neonatal features: Lymphoedema, webbed neck, coarctation of the aorta, renal anomalies Other features include: Short stature, infertility due to streak gonads or premature ovarian failure (if mosaic TS), educational or behavioural problems
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  • 45,X Turner syndrome (a) Puffy feet. (b) redundant skin at back of neck. (c) Histology of gonads: ovarian cortical strome devoid of germ cell elements
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  • Down Syndrome 1 in 700 live births >60% spontaneously aborted 20% stillborn Facial appearance permits diagnosis Marked muscle hypotonia as baby Single palmar crease may be present Learning difficulty (IQ usually


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