Germ Cells and Gametes

There is another common form of asexual reproduction that is clearly important to all multicellular organisms, and that is reproduction of somatal (or body) cells. These cells do not form gametes (or germ cells), and die when the organism dies. However, they reproduce in order to support growth or heal wounds. 

Aneuploidy in live births and abortions arises from aneuploid gametes during germ cell meiosis. Trisomy or monosomy of large chromosomes leads to early embryonic death. Trisomy of the smaller chromosomes allows survival but is detrimental to the health of an affected person, for example, Down s syndrome (trisomy 21), Patau syndrome (trisomy 13) and Edward s syndrome (trisomy 18). Sex chromosome trisomies (Klinefelter s and XXX syndromes) and the sex chromosome monosomy (XO), known as Turner s syndrome, are also compatible with survival. 

A positive response in the rodent dominant lethal test indicates that the test substance may be genotoxic in the germ cells of the treated sex of the test species as evaluated by an increase in the number of dominant lethals evaluated as the sum of pre- and postimplantation loss. A dominant lethal mutation is one occurring in a germ cell, which does not cause dysfunction of the gamete but which is lethal to the fertilized egg or developing embryo. 

GAMETE A mature germ cell (i.e., a sperm or an egg) possessing a haploid chromosome set and capable of initiating formation of a new organism by fusion with smother gamete. 

Tates, A.D. Microtus oeconomus (Rodentia), a useful mammal for studying the induction of sex-chromosome nondisjunction and diploid gametes in male germ cells. Environ. Health Perspect. 31 151-159, 1979. 

The human reproductive cells (ova and sperm) may be used for research provided free and informed consent is given. Use of gametes derived from cadavers is prohibited and use of gametes from fetuses or individuals unable to consent for themselves is deemed unacceptable. The use of gametes acquired by commercial transaction is considered unethical. Creation of hybrid individuals (e.g., a mix of human and animal gametes or transfer of somatic or germ cell nuclei between cells of humans and other species) is unethical and does not show consideration for human life and dignity. 

In the systems that have been studied, it can be seen that cells destined to become the female germ line are identified and set aside very early in development. In the female, these cells will go on to form the eggs, and will contain the mitochondria that will pass to the next generation. When one of these eggs is fertilised, the cells that will form the gametes for the next generation are set aside, and so on. 

Essential for assessment of the impact of pollutants at population level is the distinction that is made between somatic and germ-line mutations. Mutations in somatic cells may (among other effects) induce neoplasia, but because they do not occur in cells that give rise to gametes the mutation will not be passed on to the next generations. 

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