Karyotypes and Mutations-P

Karyotypes

  • Definition: A karyotype is a photograph of an individual's chromosomes grouped in pairs of homologous chromosomes by size.

  • Composition: Each person has a total of 46 chromosomes, consisting of 22 pairs of autosomes and one pair of sex chromosomes (XX or XY).

  • Identifying Sex:

    • Chromosome set 23 indicates sex:

      • XX = Female

      • XY = Male

Analyzing Karyotypes

  • Normal human karyotype contains 46 chromosomes.

  • Each of the first 22 sets should have 2 chromosomes.

  • Important checks include:

    • Presence of 2 chromosomes in each autosome set.

    • Absence of large portions missing from chromosomes.

Limitations of Karyotypes

  • Karyotypes do not show:

    • Individual DNA strands or genes.

    • Specific DNA sequences.

    • Number of genes in chromosomes.

    • Presence of gene mutations.

Chromosomal Abnormalities

  • Abnormalities often stem from nondisjunction during meiosis, where homologous chromosomes fail to separate.

  • This can result in daughter cells having too many (2n) or too few (0n) chromosomes.

Genetic and Chromosomal Disorders from Nondisjunction

  1. Down Syndrome (Trisomy 21)

    • 47 chromosomes with an extra copy of chromosome 21.

    • Characterized by short stature, mental retardation, and characteristic facial features.

    • High chance of living into adulthood.

  2. Edwards Syndrome (Trisomy 18)

    • 47 chromosomes total.

    • Very few survive past birth; low survival rate of less than 1 year.

    • Symptoms include severe mental impairment, organ defects, and physical abnormalities (e.g., clenched hands).

  3. Klinefelter's Syndrome (Trisomy XXY)

    • Extra X chromosome in males (47 chromosomes in total).

    • Symptoms include low testosterone, taller stature, and delayed puberty.

  4. XYY Syndrome (Jacob's Syndrome)

    • Males with an extra Y chromosome (47 chromosomes).

    • Often taller, may possess learning disabilities.

  5. XXX Syndrome (Trisomy X)

    • Female with an extra X chromosome (47 chromosomes total).

    • Generally develop normally but may face sterility or learning issues.

  6. Turner Syndrome (Monosomy X)

    • 45 chromosomes with a missing second X chromosome.

    • Symptoms include being shorter than average, sterility, and learning delays.

Mutations

  • Gene Mutations: Small-scale changes affecting a single gene; can be transmitted to offspring and may result in genetic disorders (e.g., sickle-cell disease, Tay-Sachs disease, cystic fibrosis).

  • Chromosomal Mutations: Large-scale alterations affecting many genes, including:

    • Deletions: Parts of chromosomes are lost (e.g., Angelman syndrome).

    • Duplications: Segments are duplicated, potentially causing disorders related to developmental delays.

    • Inversions: Segments swap places; often no symptoms.

    • Translocations: Segments of chromosomes switch places; can lead to serious genetic issues.

Impacts of Mutations

  • Mutation effects range from neutral to lethal. Significant changes can impede fetal development, often leading to miscarriage or severe disabilities.

  • Chromosomal mutations, affecting larger regions of DNA, significantly increase the risk of adverse health outcomes compared to minor gene mutations.