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The following question came up in my biology examination but I could not answer it:

"What animal produces male gametes by mitosis?"

I know that some plants produce their gametes by mitosis in the gametophytes, but found no references to any animals doing so.

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  • $\begingroup$ I don't think gametes are ever produced by mitosis. There can be modified meiosis in which there is no halving of the number of chromosomes. This can be seen in haploid organisms such as male honeybees. $\endgroup$ – WYSIWYG Apr 19 '16 at 13:30
  • $\begingroup$ @WYSIWYG correct, but it is so because male honey bees are produced by parthenogenesis. So all cells in them are haploid and can act as gametes. $\endgroup$ – another 'Homo sapien' Apr 19 '16 at 13:54
  • $\begingroup$ @another'Homosapien' No the cells do not automatically act as gametes. Sperm is a very specialized cell. Spermatogenesis does happen (see my answer). $\endgroup$ – WYSIWYG Apr 19 '16 at 14:11
  • $\begingroup$ I think the answer of honeybees is much correct,as their cells are haploid they have to produce their gametes by mitosis, because the worker bees are diploid and they are produced after fertilization so the queen and the male gametes have to be haploid. $\endgroup$ – Asmaa Apr 19 '16 at 14:33
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    $\begingroup$ @another'Homosapien' yes and as I mentioned in my answer, it still behaves like a meiosis but is finally just like mitosis. $\endgroup$ – WYSIWYG Apr 20 '16 at 19:54
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In organisms which have haploid males (such as honeybees), there is a variation of meiosis during spermatogenesis. The meiosis-I is abortive i.e. the chromosomal events such as crossover and separation of homologous chromosomes, do not happen. However, some cytological changes do happen which is described by Sharma et al (1961) as "simulation of the normal meiosis I". This is followed by meiosis II (which is mechanistically same as mitosis). So, basically there is no halving of the number of chromosomes and the gametes are also haploid.

So, as far as I can guess, the question in your exam sheet probably refers to spermatogenesis in Hymenopteran haploid males.


Reference:
Sharma, G. P., Brij L. Gupta, and C. G. Kumbkarni. "CYTOLOGY OF SPERMATOGENESIS IN THE HONEY‐BEE, APIS INDICA (F.)." Journal of the Royal Microscopical Society 79.4 (1961): 337-351.

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