Chapter 26: The Reproductive System

Module 26.1 Overview of the Reproductive System and Meiosis

Introduction to the Male and Female Reproductive Systems

The reproductive system is a defining feature of living organisms, essential for the survival of a species, though not necessary for the survival of individuals. In humans, the reproductive system remains largely inactive until puberty, when reproductive organs mature and become functional.

• Gonads (primary sex organs): The most important organs in both males and females; they secrete sex hormones (e.g., testosterone, estrogen).

• Gametes: Gonads produce gametes (sex cells) via meiosis. Male gametes are called sperm, female gametes are called ova (egg cells).

• Accessory reproductive organs: Additional structures that support the function of the reproductive system.

Overview of Meiosis

Cell division in the body occurs by two main processes: mitosis and meiosis. Mitosis produces identical daughter cells for growth and repair, while meiosis is a specialized division that produces gametes with half the number of chromosomes.

• Fertilization: The process by which sperm and egg fuse to form a single-celled offspring called a zygote.

• Zygote: Divides to produce all cells of the new individual; must have the correct number of chromosomes (half from each parent).

Meiosis: Chromosome Number and Cell Types

• Meiosis: Produces daughter cells with half the number of chromosomes (haploid, n), ensuring gametes and zygotes have the correct chromosome number.

• Somatic cells: All human somatic cells have 46 chromosomes (23 pairs) and are diploid (2n), meaning they have a full paired set.

Homologous Chromosomes and Genetic Variation

• Paternal chromosomes: Inherited from the father.

• Maternal chromosomes: Inherited from the mother.

• Each chromosome pair contains the same genes (segments of DNA coding for specific proteins), called homologous chromosomes.

• Matching genes on homologous chromosomes may have different variants (alleles), contributing to genetic diversity.

Example: The diagram shows a pair of homologous chromosomes, one from each parent, with the same genes but possibly different alleles.

Additional info: Meiosis introduces genetic variation through processes such as crossing over and independent assortment, which shuffle alleles and increase diversity among offspring.