Understanding DNA, Genetics, and Cell Division

DNA and Genetic Information

The DNA molecule transfers information between living organisms with the capacity for self-replication. It contains genetic information encoded for the individual and belongs to the group of nucleic acids.

Nucleic Acids

A nucleic acid is a biomolecule consisting of a long chain that stores genetic information, built around the repetition of units called nucleotides.

Nucleotide Structure

Both DNA and RNA consist of three elements: 1) Nitrogenous base, 2) Sugar (ribose or deoxyribose), and 3) Phosphate group.

Nucleobases

The primary bases are adenine, thymine, cytosine, and guanine. In RNA, thymine is replaced by uracil. Base pairing follows the rule: AT / GC.

Chromosomes and Species

• The human species is diploid, possessing 23 pairs of chromosomes (46 total).
• The horse has 64 chromosomes (2n = 64), with 32 chromosomes in its sex cells.
• Only one pair of chromosomes determines the sex of the individual.

DNA Replication

Replication is the process of DNA duplication, creating an identical copy of the original molecule.

Mitosis: Somatic Cell Division

Mitosis is the process by which somatic (non-reproductive) cells divide:

• Stage 1 - Prophase: The cell undergoes centriole duplication.
• Stage 2 - Metaphase: Chromosomes align on the equatorial plane, and centrioles move to opposite poles.
• Stage 3 - Anaphase: Chromatids are separated and pulled toward opposite poles of the cell.
• Stage 4 - Telophase: Duplication of cellular organelles begins, followed by cytokinesis.

Mutations

A mutation is an alteration in DNA, which can occur randomly or due to specific environmental factors.

Haploid and Diploid Cells

• Haploid: An organism consisting of a single set of chromosomes.
• Diploid: An organism containing two copies of each chromosome.
• Autosomes vs. Heterochromosomes: 22 of the 23 pairs are autosomes, which do not contain information regarding sexual characteristics. The remaining pair consists of heterochromosomes, which determine the sex of the individual.

Genotype and Phenotype

• Genotype: The specific genetic makeup or set of alleles present in an individual or species.
• Phenotype: The physical expression of the genotype, modulated by interaction with the environment.