PHYLUM: PROTOZOA Asexual Reproduction By:AAKRITI
ASEXUAL REPRODUCTION IN PROTOZOANS Asexual reproduction is the method in which reproduction occurs without the fusion of pronuclei Asexual reproduction does not generate new genetic recombination. .The offspring show uniparental inheritance, without any genetic variations. In protozoans, asexual reproduction occurs only under favorable conditions.
The following are different modes of asexual reproduction occurring in protozoans Binary Fission: It is the most common method of asexual reproduction where in the parent divides into two daughter individuals. It involves division of nucleus followed by the division of the cytoplasm. The plane of fission differs in different protozoans.
Depending on the plane of fission binary fission is of following types: Irregular binary fission: Binary fission is irregular in some of the protozoans which do not have defined body shape. In these protozoans, there will be no defined plane of fission either and hence the name irregular binary fission. Example:Amoeba Longitudinal binary fission: Longitudinal binary fission is common in Mastigophoran protozoans and in few ciliophorans also. This type of fission process starts at the anterior end and proceeds towards the posterior end. The plane of fission is parallel to the longitudinal axis of the body of the organism. Example:Euglena, Vorticella
Fig. 1.3. Types of Binary fission in Protozoas. A. Irregular in Amoeba; B. Longitudinal in Euglena; C. Transverse in Paramecium.
Transverse binary fission: Transverse binary fission is seen in ciliate protozoans. The plane of fission in this type is at right angles to the kineties. All the paramecia produced asexually by repeated binary fission from a single parent constitute a clone. Example:Paramecium Oblique Binary fission: Oblique binary fission is common in some protozoans like dinoflagellates. In this type the plane of fission is oblique to the body axis of the organism. Example:Ceratium
Fission point OBLIQUE BINARY FISSION Eg: Ceratium
Multiple Fission: It is the division of the parent into numerous daughter individuals. Nucleus divides into many nuclei followed by the cytoplasmic division forming many daughter individuals. It is prominent in Sporozoans and Sarcodines. Schizogony is the asexual kind of multiple fission and its end products of schizogony grow into trophozoites. Gamogony is the sexual kind of multiple fission by which gametes are formed. Also sporogony is also sexual kind of multiple fission by which spores are formed. Example:Aggregata
CRYPTO MEROZOITE SCHIZONT NUCLE EMEROZOITES Fig.1.5. Mtiple fission of malarial parasite in RBC of man.
Budding: It is common in suctorian protozoans. The bud is a smaller individual formed after nuclear division Monotonic budding (Vorticella) is seen in ciliates whereas multiple budding is seen in suctorians. Buds can occur either exogenously (Ephelota) or endogenously (Acineta) in some of the protozoans. Example:Acineta, Ephelota, Vorticella Plasmotomy: It is the division of a multinucleate protozoan into multinucleate daughter individuals by cytoplasmic division but without nuclear divisions. The parental nuclei are distributed among the daughter individuals. Example:Opalina, Pleomyxa
Nuclei Individual multinucleated daughters PLASMOTOMY Eg: Pleomyxa
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