Biology Chapter: Reproductive Systems & Cell Division

Reproductive System: Gametogenesis

• Gametogenesis encompasses spermatogenesis (male gamete production) and oogenesis (female gamete production)
• Spermatogenesis occurs continuously in males, while oogenesis is cyclical in females, pausing until puberty
• Spermatogenesis results in four haploid sperm cells, whereas oogenesis yields one mature ovum and two or three polar bodies
• Timing and quantity of gamete production, as well as endocrine regulation, differ significantly between sexes

Mitosis and Meiosis

• Mitosis is cell division that produces two genetically identical daughter cells with the same chromosome number (diploid). It maintains chromosome count.
• Meiosis is a two-stage cell division process that reduces the chromosome number from diploid to haploid. This is crucial for sexual reproduction.

Cell Division by Mitosis

• Chromosomes replicate, forming sister chromatids.
• Chromosomes divide evenly, resulting in two daughter cells identical to the original cell (diploid).

Cell Division by Meiosis

• Meiosis is a two-stage process (Meiosis I and Meiosis II).
• Meiosis I: Replication, homologous chromosome pairs separate reducing the chromosome number to haploid
• Meiosis II: Sister chromatids separate, producing four haploid gametes

Meiosis Produces New Combinations of Genes

• Independent assortment: During Metaphase I, maternal and paternal homologous chromosomes randomly align, generating diverse combinations of chromosomes in gametes
• Crossing over: In Prophase I, homologous chromosomes exchange segments, creating new combinations of genes on each chromosome.

Gametogenesis and Fertilization

• Gametogenesis refers to the production of gametes (sperm and egg).
• Fertilization is the fusion of male and female gametes, combining their genetic material to create a zygote.

Spermatogenesis (Male Gamete Production)

• Spermatogonia (stem cells): Continuously divide by mitosis.
• Primary spermatocytes (diploid cells): Undergo Meiosis I, resulting in secondary spermatocytes
• Secondary spermatocytes (haploid cells): Undergo Meiosis II, producing spermatids
• Spermatids (haploid cells): Mature into sperm through spermiogenesis
• Spermiogenesis: Differentiation of spermatids into functional sperm cells (including acrosome formation)

Spermiogenesis

• Acrosomal vesicle formation
• Flagellum production
• Mitochondria gathering around flagellum to provide energy

Spermatozoa Anatomy

• Head: Nucleus and acrosome
• Mid-piece: Mitochondria
• Tail: Whip-like flagellum

Oogenesis (Female Gamete Production)

• Oogonia (stem cells): Divide by mitosis before birth.
• Primary oocytes: Enter Meiosis I but arrest until puberty.
• Secondary oocyte: Result of Meiosis I, arrested at Meiosis II, released monthly.
• Ovum (egg): Meiosis II completion occurs only if fertilization is successful.
• Uneven cytoplasmic division results in one mature ovum one polar body/two to three
• Oogenesis occurs in the ovaries; each month, some primary oocytes complete meiosis I, forming a secondary oocyte and polar body.

Spermatogenesis vs. Oogenesis

• Location: Testes vs. Ovaries
• Gamete Production: 4 sperm vs. 1 ovum and 2-3 polar bodies
• Gamete Size: Small sperm vs. large ovum
• Release: Continuous vs. cyclical
• Onset: Puberty vs. prenatal
• Duration: Lifelong vs. terminates with menopause