Sexual vs. Asexual Reproduction:
Normally, cellular division results in
diploid cells that are genetically-identical. This form of cellular division is known as
mitosis, and this is how normal body cells reproduce. There is a second form of cellular division, however, known as
meiosis. Meiotic cell division results in
haploid cells that have only half the normal number of chromosomes and that are
not genetically-identical. This is how the sex cells are produced.
In
sexual reproduction, males and females produce haploid sex cells known as
gametes through meiosis. The male gametes (
spermatozoa) are small and mobile. The female gametes (
ova) are much larger and are non-mobile. A haploid spermatozoan and a haploid ovum unite at
fertilization to produce a
zygote that is
diploid (that is, it has a complete set of chromosomes). The zygote ultimately grows into a new individual that is genetically distinct from either of its parents.
A sexually-reproducing species in which individuals can produce both spermatozoa
and ova simultaneously is said to be
monoecious or
hermaphroditic. A species in which each an individual can produce either spermatozoa
or ova, but not both at the same time, is said to be
dioecious.
In
asexual reproduction, there is no union of spermatozoan and ovum, so only one parent is involved. Usually, asexual reproduction involves reproduction through
mitosis and the production of an offspring that is genetically-identical to its parent – that is, it is a
clone of its parent.