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MCB (Subject) / Genetics (Lesson)

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• Def. Cytogenetics "Study of the structure of chromosomes and looking for alterations in chromosome number and structure" Constitutional abnormality = in all cells Somatic abnormality = in some cells/tissues 
• Karyotyping (Process) - Culturation of tissue sample --> Cell proliferation --> Disruption of mitotic spindle and lysis of nuclear membrane --> application of Giemsa stain -->stains regions rich in A and T, producing dark bands - --> Identification of chromosomal by banding patterns 
• Chromosome abnormalities (2) 1. Numerical - gain or loss of complete chromosomes a) Polypoidy - extra complete set of chromosomes (69XXX) b) Aneuploidy - one or more chromosomes extra/missing  - autosomal (Down syndrome, Cs 21) - sex chromosomes (Klinefelter's, 47, XXY) 2. Structural - Causes: recombination between non-homologous chromosomes, breaking of double strand DNA in chromatids, wrong separation of centromere pair during meiosis  a) Balanced - no loss of genetic material b) Unbalanced - loss if genetic material 
• Types of mutation 1. Point mutation - single base pair changes  a) Silent mutation - no change in AA sequence (redundancy of genetic code) b) Missense mutation - one AA replaced by another  c) Nonsense mutation - Stop codon instead of an AA  2. Frameshift mutation - Insertion or deletion of a number of nucleotides that is not divisible by three --> all AAs change beyond the insertion 3. Deletion - deletion of on or more bps of DNA 4. Insertion - insertion of one or more bps in the DNA
• Causes of mutation (2) 1. Spontaneous - Instability of 4 DNA nucleotides - Mistakes made by DNA polymerase  - Imperfect meiosis  2. Induced  - chemicals can covalently bind to nucleotide bases or add chemical groups to it - radiation can damage DNA (UV, radiation) 

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