Page 9 - Kingdom Protist

Figure 2.3
Paramecia are unicellular organisms with membrane-bound organelles. They undergo
a process called conjugation in which a pair of paramecia will exchange genetic
information as shown in the diagram at the bottom of the page. This is not considered
sexual reproduction because new individuals are not formed.

Reproduction in ciliates
Ciliates reproduce asexually by binary fission. During this process, the

macronucleus elongates and splits rather than undergoing mitotic division. Most
ciliates maintain genetic variation by undergoing conjugation—a sexual process in
which genetic information is exchanged. Conjugation is considered a sexual process,
but it is not considered sexual reproduction because new organisms are not formed.

The process of conjugation for Paramecium caudatum is typical of most ciliates and
is illustrated in Figure 2.3 During conjugation, two paramecia form a cytoplasmic
bridge and their diploid micronuclei undergo meiosis. After three of the newly

formed haploid micronuclei dissolve, the remaining micronucleus undergoes mitosis.
One micronucleus from each connected cell is exchanged, and the two paramecia

separate. The macronucleus disintegrates in each paramecium, and the micronuclei
combine and form a new, diploid macronucleus. Each cell now contains a
macronucleus, micronuclei, and a new combination of genetic information.

6