Chromosomes_1

Overview of Chromosomes

• Chromosomes from a human cell are isolated from its nucleus and can be visually represented.

• Human males have 22 pairs of autosomes and one pair of sex chromosomes (X and Y).

• Chromosome visualization includes dark and light bands created by specific staining techniques.

  • Dark spots correspond to densely packed areas of DNA.

  • Light spots represent less densely packed areas.

Karyotyping Techniques

• Traditional Karyotyping:

  • Requires extensive training in cytogenetics to identify and visualize chromosomes.

  • Chromosomes are matched based on size and banding patterns.

• Spectral Karyotyping (Sky Test):

  • Utilizes fluorescent tags that allow for differentiation of chromosomes under a computer's analysis of spectrums.

  • Provides the ability to visualize changes in chromosome structure and number more efficiently than traditional staining.

  • Useful in identifying abnormal chromosome numbers or structural changes.

General Chromosome Information

• Every somatic cell in the human body typically contains 23 pairs of chromosomes, totaling 46.

• Gametes (sperm and eggs) contain half this number (haploid).

• Red blood cells lose their chromosomes during development and do not contain DNA in mature cells.

• The number of chromosomes can vary among different organisms.

Changes in Chromosomal Number

• Two main concepts related to chromosomal changes: Euploidy and Aneuploidy.

  • Euploidy: Involves the change of whole sets of chromosomes (e.g., from diploid 2n to tetraploid 4n).

  • Aneuploidy: Refers to changes in the number of chromosomes where part of a chromosome set is added or lost.

Fundamental Definitions

• Diploid: Normal chromosome count represented as 2n, where n is the number of homologous pairs (23 in humans).

• Haploid: Gametes have only one set of chromosomes (n).

Aberrant Euploidy and Polyploidy

• Aberrant Euploidy or Polyploidy: Refers to having more than two complete chromosome sets.

  • Examples: Triploid (3n) and Tetraploid (4n) organisms.

• Monoploid: Defined as organisms having a haploid number of chromosomes (1n).

  • Monoploid organisms are generally sterile.

Mechanisms of Polyploidy

• Autopolyploids: Intra-species chromosome set doubling typically caused by meiotic errors leading to unreduced gametes.

• Allopolyploids: Hybridization involving chromosome set changes between different species, often resulting in a new fertile species.

Polyploidy in Plants vs. Animals

• Polyploidy is common in plants and can lead to increased size and vigor in crops.

• In contrast, animals generally do not survive significant changes in chromosome numbers beyond fertilization, as it often results in miscarriage.

• Examples of polygonal plants include cultivated crops like strawberries that are engineered to be octoploid for enhanced yield.

Examples of Applied Polyploidy in Agriculture

• Colchicine Treatment: Inhibits microtubule formation during meiosis, allowing for the creation of polyploid plants (e.g., octoploid strawberries and seedless grapes).

• Triploid Plant Examples: Seedless fruits, including bananas and certain oyster species (triploid oysters), are cultivated in agriculture for consistent production and quality.

Conclusion on Chromosomal Changes

• Understanding chromosomal changes aids in plant breeding, agriculture, and genetics.

• The upcoming discussions will further elaborate on structural chromosome changes.