GM

Notes on Cellular Basis of Reproduction and Inheritance

Introduction to Cell Division and Reproduction

  • Understanding the cellular basis of reproduction and inheritance is critical in biology.

Why Do Cells Divide?

  • Cells divide for several reasons including:
  • Growth.
  • Repair of tissues.
  • Asexual and sexual reproduction.
  • Important concepts to note:
  • Surface area vs. Volume: As cells grow, their volume increases faster than surface area, which necessitates division.

Cell Division

  • Cells originate only from preexisting cells (Cell Theory).
  • Two Types of Reproduction:
  • Asexual: Organisms produce offspring identical to themselves (e.g., yeast, starfish).
  • Sexual: Involves combining genetic material from two parents leads to genetic diversity.

Cell Cycle Phases

  • Interphase: Preparation for mitosis consisting of three phases:
  • G1 (cell growth)
  • S (DNA synthesis)
  • G2 (preparing for mitosis)
  • M Phase: Cell division, consisting of mitosis and cytokinesis.

Mitosis

  • Definition: Division of somatic (body) cells.
  • Phases:
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • Important outcome: Produces two genetically identical diploid daughter cells.

Cytokinesis

  • Animal cells: Form a cleavage furrow.
  • Plant cells: Form a cell plate, which develops into a new cell wall.

Meiosis

  • Definition: Specialized type of cell division reducing chromosome number from diploid to haploid, essential for sexual reproduction.
  • Processes:
  • Meiosis I: Homologous chromosomes separate.
  • Meiosis II: Sister chromatids separate, resulting in four haploid cells.
  • Key Features:
  • Crossing over: Exchange of genetic material between homologous chromosomes, increasing genetic variability.

Chromosome Structure & Types

  • Autosomes: Non-sex chromosomes.
  • Sex chromosomes: Determine biological sex (e.g., XX for female, XY for male).
  • Homologous Chromosomes: Chromosomes that carry the same type of gene.
  • Karyotypes: Used to analyze chromosome number and structure abnormalities.

Genetic Variability

  • Produced through:
  • Independent assortment of chromosomes during meiosis.
  • Crossing over during prophase I.
  • Random fertilization of gametes.

Cancer and Cell Division

  • Uncontrolled cell division can lead to cancer.
  • Cancer cells often evade cell cycle controls, leading to tumor formation.
  • Treatment often involves targeting rapidly dividing cells (chemotherapy, radiation).

Important Terminology

  • Diploid (2n): Two sets of chromosomes (e.g., human somatic cells: 46 chromosomes).
  • Haploid (n): One set of chromosomes (e.g., human gametes: 23 chromosomes).
  • Nondisjunction: Failure of chromosome pairs to separate correctly during meiosis, potentially leading to conditions like Down syndrome.

Conclusion/Connections

  • Understanding the processes of cell division is vital for grasping basic biological functions and implications in health and disease.
  • The study of genetics through these processes also provides insight into evolution, biodiversity, and conservation efforts.