Biology Reference
In-Depth Information
DNA
DNA
replication
Cell
elongation
Septum formation
Completion of
septum with
formation of
distinct walls
Cell separation
Figure 2.14 Asexual reproduction (binary fission) in bacteria.
Source : From mtsu32.mtsu.edu:11289/cellcycle_web/sld006.htm . Accessed in June 2012.
Binary Fission in Bacteria
Having no separate sexes, bacteria reproduce asexually. Binary fission is their main
mode of reproduction ( Figure 2.14 ). Bacterial DNA is condensed in a circular chro-
mosome in a region called the nucleoid , which in the bacterium Escherichia coli rep-
resents one-third of the cell volume ( Harrington and Trun, 1997 ). The cytoplasm also
divides equally between the two resulting cells, so both cells are similar.
Budding in Bacteria
Many bacteria use budding for reproduction. The mother cell produces a small bud
on one of its ends. The bud grows on the mother's body and, depending on the spe-
cies, separates when it grows to a size comparable to its mother's size ( Figure 2.15 ).
Other forms of asexual reproduction in unicellulars include multiple fission and
spore formation (sporulation).
Whether one talks of sexuality in bacteria depends on the definition of sexuality;
if sexuality implies separate sexes, and the exchange of genetic material is a pre-
requisite of sexual reproduction, then bacteria could hardly be considered sexually
reproducing organisms (conjugation is not a prerequisite of bacterial reproduction).
It is true that during conjugation, bacteria exchange genetic material (DNA), but the
exchange is not part of bacterial reproduction, and there are no genuinely separate
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