I have found the following definitions of different types of gametes:

  • isogametes: gametes looking and behaving the same;
  • heterogametes: gametes different in size or in behaviour;
  • oogametes: gametes different in size and behaviour.

I have some doubts about the exact meaning of behaviour in such definitions. I know that there exist species where gametes of the same mating type can originate a zygote, for ex. in some fungi. Do differing heterogametes and oogametes always belong to different mating types? Thank you very much for any clarification!

  • $\begingroup$ Where are these definitions from? Wiktionary defines a heterogamete as "Either of a pair of conjugating gametes that differ in structure or behaviour". $\endgroup$
    – augurar
    Jun 11, 2015 at 7:09
  • $\begingroup$ @augurar Thank you for the comment! They are from an Italian language text. It may happen that scientific language usage is different in different countries: edited OP to fit Wiktionary's definition $\endgroup$ Jun 12, 2015 at 7:48
  • $\begingroup$ What do you mean with "Do differing eterogametes and oogametes always belong to different mating types?"? That different individual gametes always belong to different mating types, or that different types of oogametes (e.g. egg and sperm) always belong to different mating types? $\endgroup$ Jun 12, 2015 at 11:47
  • $\begingroup$ @fileunderwater I mean "Do the different types of oogametes (or heterogametes) necessarily belong to different mating types (ex.: + and -) (or can they be produced by the same mating type)?". I'm basically looking for definitions as rigourous and precise as possible. Thank you for the comment! $\endgroup$ Jun 14, 2015 at 10:00
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    $\begingroup$ @Self-teachingworker excellent question. Me too have this question; in-addition I want to know; if such 2 type of isogamy exists (you mentioned some fungus) (type-1: any gamete can fuse with any other gamete, i.e. there is not existence of 2 sex; and type-2: all gametes looks exactly same and shows exactly same movements or activity etc, but they are of 2 types... male and female... inside, so that one sort of gamete doesn't fuse with same sort). I'm not talking about physiological anisogamy. $\endgroup$
    – user25568
    Nov 4, 2016 at 15:11

1 Answer 1


Allow me to start off with a nice picture showing the differences - note female gametes are on the left while male gametes are on the right in my examples:

Picture differences


For a gamete to be considered an isogamete the other gamete that it meets up with to produce is exactly the same in both size, structure and movement. [2] It is literally trying to find itself. The "male" and "female" are literally no different and it is impossible to tell which is which.

When you look at the picture the two gametes are exactly the same in every way except that they are facing each other in this picture.

The next two are forms of anisogamy: Picture
(source: ulsfmovie.org)


These gametes differ in at least one of the following:

  1. size
  2. structure
  3. sex

Although it can also be a combination of these three things. [3] As you can see here the female can be structurally the same as the male. (Bottom and top examples of the second picture). From my understanding (although someone can come and prove me wrong) Oogametes are a specific from of heterogamous.


Oogametes differ in size, sex AND function. Females are stationary while males move. [4] Females are also much larger than males. (For instance in humans the cell that divides to make sperm divides equally while the cell that divides in the female divides to make one egg and three polar bodies.)

  • $\begingroup$ Very kind answer! What does "sex" mean in the "heterogametes" definition? Does it mean "mating type"? I've read that isogametes undergoing fusion must belong to different mating type at least in some species (ex.: in some strains of Chlamydomonas): must any two (including iso-, hetero- and oo-) gametes undergoing fusion belong to different mating types in all organisms? I've got some doubts because, for ex., of homothallic fungi ( biology.stackexchange.com/questions/35057/… )... I heartily thank you again! $\endgroup$ Jun 25, 2015 at 8:51
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    $\begingroup$ Male vs female. Like sperm vs egg @Self-teachingDavide $\endgroup$
    – SolarLunix
    Jun 25, 2015 at 14:45
  • $\begingroup$ OK: I assume you mean male = motile, female = stationary. Thank you!!! $\endgroup$ Jun 25, 2015 at 22:33
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    $\begingroup$ Yes, exactly @Self-TeachingDavide $\endgroup$
    – SolarLunix
    Jun 26, 2015 at 7:36
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    $\begingroup$ The second picture shows nothing and when clicked, redirects to a dead link. $\endgroup$
    – user25568
    Nov 4, 2016 at 14:48

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