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.