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Key Concepts
Germ cell line

In the development of large mammalian species, such as humans, division of the original zygote cell produces somatic (body) cells and specialized germ cells which will carry the responsibility of producing the sex gametes, and thus the next generation of that species.

    Key concepts:
  • The production of sex gametes is usually the role of specialized organs within the adult form of a species; these are the gonads.
  • Within the gonads (which are mostly somatic cells), are primordial germ cells which do not specialize or differentiate, these are diploids which can, however, multiply by mitosis.
  • Depending on the species and the sex of the individual, these germ cells eventually commit themselves to producing sex gametes, sperm in the case of males and ova (eggs) in the case of females.
  • In males the primary germ cell becomes a primary spermatocyte, which undergoes two rounds of a typical meiotic division to produce 4 haploid spermatids.
  • These spermatids differentiate into motile, highly simplified sperm cells, which are the fully mature male gametes.
  • In females, the germ cell produces an Oogonium diploid cell, which becomes the primary oocyte.
  • This oocyte undergoes the first meiotic division and produces two haploid products. In humans only one of these, the secondary oocyte continues into the second meiotic division, the other product (called a polar body) has no further role.
  • The secondary oocyte proceeds through the second meiotic division producing an Ootid and a second polar body, which is discarded.
  • It is the ootid that differentiates into the mature female gamete; the Ovum.

Science@a Distance
© 2001, Professor John Blamire