Errors in mitosis

Errors in Meiosis

  • Nondisjunction: Failure of homologous chromosomes or sister chromatids to separate during meiosis.

    • Results in trisomy (2n + 1) or monosomy (2n - 1).

Errors in Chromosome Structure

  • Types of errors:

    • Duplication

    • Deletion

    • Inversion

    • Translocation

Specific Chromosomal Disorders

  • Cri du Chat: Deletion on chromosome 5; symptoms include high-pitched cry, low birth weight, cognitive delays.

  • Charcot-Marie-Tooth disease: Duplication on chromosome 17; leads to muscle weakness and loss of sensation.

  • FG Syndrome: Inversion of X chromosome; affects males leading to intellectual disabilities and delayed development.

  • Chronic Myelogenous Leukemia: Translocation between chromosomes 9 and 22; results in abnormal gene causing cancer of white blood cells.

Karyotype

  • A karyotype is a display of an individual's chromosomes; example: 46, XY.

Trisomy Disorders

  • Down syndrome (trisomy 21): Extra copy of chromosome 21; symptoms include characteristic features and increased health risks.

  • Patau syndrome (trisomy 13): Serious defects; typically fatal within months.

  • Edward's syndrome (trisomy 18): Affects most organ systems; generally not survivable beyond a few months.

Sex Chromosome Anomalies

  • Klinefelter syndrome (47, XXY): Sterile males with small testes and some feminine characteristics.

  • 47, XYY males: Taller than average, slightly below normal intelligence.

  • Trisomy X (47, XXX): Generally healthy and fertile females.

  • Monosomy X (Turner syndrome): Viable monosomy (45 chromosomes); females do not mature during puberty and are sterile.

Prenatal Testing

  • Non-invasive: Blood test, ultrasound.

  • Invasive: Amniocentesis, chorionic villus sampling; to gather information on chromosomal abnormalities and assess risk for conditions like Down's syndrome.