6.1

Cell Types

  • Somatic cells: Body cells (e.g., tissue, spleen, kidneys, eyeballs). DNA not passed directly to offspring.
  • Germ cells: Located in ovaries or testes; create gametes.
    • Female gametes: Ova (eggs).
    • Male gametes: Spermatozoa (sperm cells).

Chromosomes

  • Body cells contain genetically identical chromosomes.
  • 23 chromosomes received from each parent.
  • Homologous Chromosomes: one from each parent with same length and appearance.
  • Autosomes: Chromosomes 1-22.
  • Sex Chromosome: 23rd chromosome (X and Y system).
    • X chromosome is larger.

Sexual Reproduction

  • Fusion of gametes, offspring are genetic mixture of parents.
  • Fertilization: Fusion of sperm and egg.

Chromosome Number

  • Diploid: Body cells, 46 chromosomes in humans.
  • Haploid: 23 chromosomes in human gametes.
  • Tetraploidy: Plants with four copies of each chromosome.

Cell Division

  • Meiosis: Divides a diploid cell into haploid cells.

Mitosis vs. Meiosis

  • Mitosis: Genetically identical cells, diploid cells, occurs throughout life, involved in asexual reproduction.
  • Meiosis: Genetically unique cells, haploid cells, occurs at certain times, involved in sexual reproduction.

Meiosis

  • Reduces chromosome number in half; DNA copied once, divided twice.