Learning Objectives

  • Distinguish types of cell division.
  • Understand mitosis for cell replacement.
  • Explain meiosis for sperm and egg generation.
  • Describe sex chromosome differences.
  • Discuss consequences of abnormal chromosome numbers.

Telomeres

  • Noncoding DNA sections protecting chromosome ends.
  • Rebuilding can lead to cancer if uncontrolled.

Chromosomes

  • Eukaryotes: linear chromosomes in nucleus.
  • Prokaryotes: single circular chromosome attached to membrane.
  • Binary Fission: asexual reproduction via chromosome duplication.

Cell Cycle

  • Stages: G1 (growth), S (DNA synthesis), G2 (preparation), M (mitosis).
  • G1 includes a Go phase (resting).
  • Checkpoints ensure proper cycle regulation: DNA damage, sufficient nutrients, spindle assembly.

DNA Replication

  • Occurs in two steps: unwinding and elongation.
  • Errors can lead to mutations but also genetic diversity.

Mitosis Overview

  • Required for growth and replacement of somatic cells.
  • Process: Chromosomes condense, align, separate, and nuclear membranes reform, followed by cytokinesis.

Cancer

  • Characterized by uncontrolled cell division.
  • Features of cancer cells: lack of contact inhibition, indefinite division, reduced 'stickiness'.
  • Tumors: benign (non-spreading) vs. malignant (spreading).
  • Treatment methods: chemotherapy and radiation.

Meiosis

  • Produces haploid gametes for sexual reproduction.
  • Consists of two rounds of division: Meiosis I (homologous separation) and Meiosis II (sister chromatids separation).
  • Results in four genetically diverse haploid cells.

Gamete Development

  • In females: one large egg and polar bodies.
  • In males: smaller, motile sperm.

Genetic Variation Sources

  • Crossing over and reassortment during meiosis increases diversity.

Sexual vs. Asexual Reproduction

  • Asexual: identical offspring; efficient but less varied.
  • Sexual: varied offspring; less efficient but advantageous in changing environments.

Sex Determination

  • In humans: X and Y chromosomes (XY male, XX female).
  • Other species: diverse methods (e.g., environmental, genetic).

Chromosomal Disorders

  • Karyotype: visual display for chromosome abnormalities.
  • Down syndrome (trisomy 21): linked to maternal age and nondisjunction.

Sex Chromosome Abnormalities

  • Turner syndrome (X0): physical and reproductive challenges.
  • Klinefelter syndrome (XXY): underdeveloped testes, possible infertility.
  • XXX females and XYY males also show unique traits but may have reduced complications.
  • Most individuals with abnormal sex chromosome counts survive with varying effects.