Gametogenesis and Somatic Cells

Gametogenesis

• Gametogenesis is the conversion of germ cells into male and female gametes
• Male gamete: sperm
• Female gamete: oocyte
• Zygote: union of male and female gametes

Somatic Cell and Gametes

• Somatic cells have 46 chromosomes (23 pairs), including 22 pairs of autosomes and 1 pair of sex chromosomes
• Each gamete (maternal and paternal) contains a haploid number of 23 chromosomes

Phases of Gametogenesis

• Four phases: origin and migration of germ cells, increase in number of germ cells by mitosis, reduction in chromosomal number by meiosis, and structural and functional maturation of eggs and sperm

Mitosis and Meiosis

• Mitosis: process where a cell divides to produce two genetically identical daughter cells
• Meiosis: process that takes place in germ cells to produce gametes, requiring two cell divisions (Meiosis I and Meiosis II)

Chromosomal Abnormalities

• Numerical abnormalities: non-disjunction leads to formation of daughter cells with unequal chromosome numbers (trisomy or monosomy)
• Structural abnormalities: do not affect total chromosome number, but have serious consequences, including translocation and deletion

Early Development of Gametes

• In human embryos: undifferentiated primordial gonadal cells (PGC) are seen in the epithelium of the yolk sac at 3 weeks, and migrate to the genital ridges at 4 weeks
• PGC induce the genital ridge to differentiate into a primitive germinal epithelium, forming primary sex cords
• At 8 weeks, ovary and testis are histologically distinct

Oogenesis

• Oogenesis produces ova
• Oogonium differentiates into ovum
• Immature oocytes are distributed throughout the ovary in follicles, with a total of 200,000 to 400,000 follicles present in each human ovary
• Only a few oogonia reach maturity, with fewer than 400 oocytes maturing and being released by ovulation in humans
• Location of oocyte depends on its maturity, with primordial follicles most prevalent in the stroma and oocytes becoming more centrally located as they mature

Understand the process of gametogenesis, including the formation of male and female gametes, and the differences between somatic cells and gametes. Learn about the phases of gametogenesis and the union of gametes to form a zygote.