Biology: The Core Chapter 5 - Chromosomes and Inheritance

Cell Theory and Basics of Cell Biology

• All living organisms are composed of cells.

• Cell theory:

  • All life is cellular.

  • All cells arise from preexisting cells.

Cell Division

• Cell division forms new cells from preexisting cells.

• Purpose of cell division:

  • Growth

  • Repair

  • Reproduction (sexual and asexual)

Reproduction

Sexual Reproduction

• Involves two parents, leading to genetically unique offspring.

• Gametes (sperm and egg) are produced via cell division in gonads.

• Fertilization unites sperm and egg, creating a zygote.

Asexual Reproduction

• Involves one parent, producing genetically identical offspring.

Genetics

• DNA is the genetic material for all life.

• Chromosomes contain genes, which are segments of DNA encoding proteins/RNA.

• Chromosomes exist as chromatin, condense for cell division.

Cell Cycle and Division

Cell Cycle Phases

• Interphase (90% of cell's life): normal functions, growth, prepare for division.

• Mitotic Phase: active cell division occurs.

Stages of Mitosis

1. Prophase: Chromosomes condense; nuclear membrane dissolves.

2. Metaphase: Chromosomes align at the spindle.

3. Anaphase: Sister chromatids separate.

4. Telophase: Nuclear membranes reform; two nuclei are formed.

5. Cytokinesis: Cytoplasm divides, resulting in two cells.

Meiosis

• Special cell division for gamete formation.

• Results in haploid cells (sperm and egg).

• Stages of Meiosis:

  • Meiosis I: Homologous chromosomes separate.

  • Meiosis II: Sister chromatids separate.

• Nondisjunction: failure of chromosomes to separate, leading to abnormal chromosome numbers (e.g., Down syndrome, Turner syndrome).

Genetic Variation in Sexual Reproduction

• Independent assortment: random arrangement of chromosomes.

• Random fertilization: vast combinations of sperm and egg.

• Crossing over: exchange of genetic material between homologous chromosomes during meiosis, increasing variability.