= Anisogamy
<Anisogamy> is <sexual reproduction> involving two classes of <gametes> that differ in size. The larger <gamete> defines the female reproductive role, and the smaller <gamete> the male role. In <humans>, an <ovum> and a <sperm> illustrate the distinction. Mobility is a separate character: the definition is not simply that one <gamete> moves and the other does not.
A resource-budget model makes the evolutionary tension visible. With total investment $B$ and mass $m$ per <gamete>, the number produced is $B/m$. Smaller <gametes> can be more numerous, whereas a larger combined contribution can improve survival of the resulting <zygote>. Models ask when these competing effects favor distinct size classes rather than a single intermediate size; the answer depends on their assumptions about encounters and <biological fitness>.<The origin and evolution of gamete dimorphism and the male-female phenomenon by G. A. Parker and others>[Journal of Theoretical Biology 36, pp. 529–553; gamete productivity and zygote-size-dependent fitness]{ref}
Back to article page
