Chromosome Structure and Functions

Chromosome Structure and Functions

• Human body contains 46 chromosomes organized into 23 pairs (diploid).
• Homologous chromosomes are pairs of chromosomes of the same length and appearance, inherited from each parent.
• Two main types of chromosomes:
  • Autosomes: Chromosomes 1-22 (non-sex chromosomes).
  • Sex Chromosomes: The 23rd pair, determining the biological sex of an individual.

Sex Chromosomes

• Female sex chromosomes: XX.
• Male sex chromosomes: XY.
• X is the largest sex chromosome, while Y is the smallest.

Karyotyping

• Karyotyping is a technique used to visualize a complete set of chromosomes.
• Chromosomes are grouped in pairs and arranged from largest to smallest, resulting in a karyogram.

Meiosis and Chromosomal Abnormalities

• Expected chromosome number after meiosis is 23.
• Errors during meiosis can lead to abnormal chromosome counts, resulting in chromosomal abnormalities.
• Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate during meiosis, leading to various forms of aneuploidy.

Ploidy Levels

• Euploidy: Normal number of chromosome sets in a cell.
• Aneuploidy: Abnormal number of chromosomes, which can be due to missing or extra chromosomes.
• Types of aneuploidy include:
  • Monosomy: Presence of only one chromosome from a pair.
  • Trisomy: Presence of three copies of a chromosome.

Examples of Chromosomal Abnormalities

• Turner Syndrome (45, XO):

  • Affects females with a single X chromosome.
  • Symptoms include underdeveloped reproductive organs, short stature, webbed neck, and swelling of hands/feet.

• Down Syndrome (Trisomy 21):

  • Caused by three copies of chromosome 21.

• Klinefelter Syndrome (47, XXY):

  • Males with one or more extra chromosomes (can be 48, XXXY or 49, XXXXY).
  • Symptoms include underdeveloped reproductive organs, delayed puberty, and language-based learning disabilities.

• Jacob Syndrome (47, XYY):

  • Males with an extra Y chromosome; sometimes referred to as Supermale or Criminal Syndrome.

• Trisomy X (47, XXX):

  • Females with an extra X chromosome, typically normal in appearance but may struggle with speech, learning, and experience infertility.

Key Terms

• Nondisjunction: Failure of chromosomes to separate during meiosis.
• Karyotyping: Method to view the complete set of chromosomes.
• Karyogram: The resulting visual output from karyotyping.
• Chromosomal abnormalities arise from errors in cell division or duplications/deletions of chromosome segments.