Chromosomes & Mutation

  • Genetics: Derived from Greek "gennan" meaning 'to generate'. Study of heredity, inheritance, and variations. Basis for understanding organism makeup and disease processes.

  • Chromosomes: Genes located on chromosomes of gametes, passed from parents to progeny. Humans have 46 chromosomes (23 pairs, diploid). Gametes have 23 chromosomes (haploid). 22 pairs are autosomes, 1 pair is sex chromosomes.

  • Chemical Constituents: DNA, RNA, Histones (basic), Non-histone proteins (acidic).

  • Chromosome Structure:

    • Centromere: Spindle fiber attachment point.

    • Chromatid: Subunit of a chromosome; can be sister or non-sister.

    • Telomeres: Ends of chromosomes, highly stable.

    • Chromomeres: Bead-like structures in some chromosomes.

  • Chromatin: Coiled DNA strands with proteins. Two types:

    • Euchromatin: Less condensed, gene-rich, active genes.

    • Heterochromatin: More condensed, gene-poor, silenced genes.

  • Chromosome Types & Functions:

    • Homologous: Same gene sequences.

    • Heterologous: Different gene sequences.

    • Functions: Carry genetic information, protect DNA during cell division, ensure accurate DNA distribution.

  • Karyotype and Karyotyping: Morphology of somatic chromosomes. Karyotyping: Pairing and ordering chromosomes for a genome overview. G-banding technique for identifying genetic diseases.

  • Chromosome Mutations:

    • Structural Aberrations: Deletion, duplication, inversion, translocation.

    • Numerical Aberrations: Polyploidy (e.g., 3n, 4n), aneuploidy (gain/loss of individual chromosomes).

  • Lyon Hypothesis and X Inactivation: In females, one X chromosome is active, the other is inactivated (Barr body). Barr bodies number = total X chromosomes - 1.

  • Genetic Disorders via Karyotyping:

    • Down Syndrome: Trisomy 21 (intellectual disability, heart defects).

    • Turner Syndrome: Monosomy X (short stature, infertility).

    • Klinefelter Syndrome: XXY (tall male, infertility).

  • Mutations: Changes in DNA bases:

    • Substitution: Transition (same type base swap) / Transversion (base type swap).

    • Nonsense (premature stop codon), missense (amino acid change), silent (no change).

    • Frameshift: Insertions/deletions altering the reading frame.

    • Translocation: Segment moves within DNA.