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Genetics key concepts

4 revision pages for Genetics, each with the key facts, a memory aid where one helps, and the exam traps.

  1. Chemotherapy resistance: selection of pre-existing resistant clones

    Chemotherapy kills sensitive cells, so it usually selects resistant clones (sub-populations of cells) already in a heterogeneous tumour (one with many clones that carry slightly different mutations), which expand.

  2. Non-homologous end joining: template-free repair of double-strand breaks

    Non-homologous end joining (NHEJ) repairs a double-strand break, where both DNA strands are cut, by directly joining the broken ends, with no template (an undamaged DNA copy).

  3. Promoter and TATA box in transcription initiation

    The promoter is the DNA region at the start of a gene where transcription factors (proteins that attach to DNA and switch genes on) gather to start transcription.

  4. Trisomy and reading a karyotype: Down syndrome 47,XX,+21

    Trisomy means one extra copy of a single chromosome, giving 47 in total; Down syndrome is usually trisomy 21, with an extra chromosome 21.

Practice Genetics questions