The Reproductive System — Overview

The Reproductive System — Overview

• Works to ensure survival of the species of the animal

• Interacts with other body systems

  • Purely reproductive structures are not essential to the life of an animal

• Requires a second animal (of the opposite sex) to fully carry out its function

• Process begins with fertilization

  • Head of spermatozoon must penetrate into the cytoplasm of ovum

Chromosomes

• Genetic material in body's cells

• Coiled masses of DNA in the nuclei of cells

• Each cell in an animal's body (except gametes) contains identical chromosomes

• Diploid chromosome number = 2n

  • Total number of chromosomes in the nucleus of each body cell is the same (except gametes)

  • Always an even number — chromosomes occur in pairs

Sex Chromosomes

• One of the pairs of chromosomes that make up the diploid chromosome number

• Designated as either "X" or "Y" chromosomes

  • Both sex chromosomes "X" → individual is genetically female (XX)

  • One "X" and one "Y" → individual is genetically male (XY)

Haploid Chromosome Number

• The reduced number of chromosomes in the gamete

• Results from a reduction division (meiosis)

  • Cell divides

  • Total number of chromosomes in each daughter cell is reduced to ½ the number of the parent cell

• Ensures that the fertilized ovum (from union of ova and spermatozoa) has the diploid number

Meiosis

• Cell division that produces basic reproductive cells (ova, spermatozoa)

• Ensures the genetic makeup of each new animal is unique

Mitosis vs. Meiosis

Mitosis	Meiosis
Each chromosome produces a duplicate copy of itself	Chromosomes do not produce duplicate copies before daughter cells pull apart
Half of chromosomes go to one daughter cell, half to the other	Random half of total chromosomes go to each daughter cell
Genetic makeup exactly the same as each other and as the parent cell	—

Spermatogenesis

• The process where spermatozoa (male gametes) are produced in large numbers in the seminiferous tubules of the testes

• Sequence: Primary spermatocyte (2n, xy) → Secondary spermatocyte (n, x and n, y) → Spermatids → Spermatozoa

Oogenesis

• The process where ova (female gametes) are produced (a few at a time) in the follicles of the ovaries

• Female has a fixed number of primary oocytes at or soon after birth

• Sequence: Primary oocyte (2n, xx) → Secondary oocyte (n, x) → Ovum + Polar bodies