Process of Reproduction-in-Protists.pptx

Process of Reproduction-in-Protists

1. REPRODUCTION IN PROTISTS

2. REPRODUCTION IN PROTISTS Protists are simple eukaryotes. They have short generation time and rapid rate of reproduction. A major aspect of Protist success is their great and variable range of reproductive strategies. Most Protists have been able to capitalize on the advantages of both asexual and sexual reproduction although some reproduce only asexually.

3. TYPES OF REPRODUCTION Mode of reproduction variable in different groups : ASEXUAL REPRODUCTION SEXUAL REPRODUCTION

4. ASEXUAL REPROUCTION Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes.  It involves the mitotic division of the parent body into two or more individuals that develop into the mature or adult form. Since these are unicellular it can simply be called a type of cell division. It involves a single parent. By definition it does not generate a new genotype. It does not involve meiosis or fertilization.

5. TYPES OF ASEXUAL REPRODUCTION It is of the following types: Binary fission Multiple fission Budding Plasmotomy Endopolyogeny Regen e ration

6. BINARY FISSION It involves a single mitotic division resulting into two progenies. It results into two similar or equal progeny. It may be of the following types : i . Simple binary fission Longitudinal binary fission Transverse binary fission iv . Oblique binary fission

7. SIMPLE BINARY FISSION In this type of binary fission the plane of division can not be recognized eg . Amoeba . Nuclear division is followed by cytokinesis. Nucleus divides by mitosis which is closed i.e. nuclear membrane remains intact throughout mitosis.

8. LONGITUDINAL BINARY FISSION In this the plane of axis of division is along the longitudinal axis of the body. It cuts between the rows of basal bodies. The progenies look similar to the parent except in size. Eg . Euglena , Trypanosoma

9. TRANSVERSE BINARY FISSION In this the plane of division is transverse i.e. cuts at the middle of the antero-posterior axis. In Paramecium only the micronucleus divides by mitosis.Macronucleus divides amitotically.

10. OBLIQUE BINARY FISSION In this the plane of division is oblique. Each one develops the missing part. Eg- Ceratium

11. MULTIPLE FISSION In multiple fission , many nuclear divisions precede the rapid differentiation of the cytoplasm into many distinct uninucleate individuals. A mass of residual protoplasm may remain which is degenerated and lost. It may occur at certain phase in the life-cycle of a protist. It is common in Plasmodium ( schizogony , sporogony ), M o n oc y s ti s ( g amo g o n y , s p o r o g o n y ) , E ntamoeba ( metacyst ), Aggregata etc.

12. It is a form of unequal fission. It involves a preparatory phase before divisions In this a portion of the parent breaks off and differentiates to form a new individual. It may be of two types : A. Exogenous: Budding-occurs at the surface of the body ; eg . Ephelota, Noctiluca etc. B. Endogenous: Budding-occurs within an internal chamber or pouch . E g . Suctoria BUDDING Budding is an asexual mode of producing new organisms. In this process, a new organism is developed from a small part of the parent's body.

13. PLASMOTOMY It is considered to be a form of budding. In the multinucleate Protists the parent simply divides into two multinucleate daughter individuals, in the absence of any mitotic division. The original nuclei are distributed between the two progeny. Eg . Opalina , Pleomyxa etc ., Plasmotomy is a form of asexual reproduction occurring in protozoa, where a multinucleate cell divides into multinucleate daughter cells without mitosis. The cytoplasm divides into two or more masses.

14. ENDOPOLYOGENY It is also considered to be a form of internal budding. In this more than two offsprings are formed within the parent organism. In this two or possibly more nuclear divisions occur before merozoite formation begins. Eg . Toxoplasma gondii   Endopolygeny (uncountable) is the division into several organisms at once by internal budding

15. REGENERATION It is the replacement of the lost parts of the body. It is also a specialized type of asexual reproduction. A specific part of the protoplasm and nucleus can regenerate the entire organism. Widespread among free living Protists such as Amoeba. Not so common in parasitic Protists. Regeneration is the natural process of replacing or restoring damaged or missing cells, tissues, organs and even entire body parts to full function in plants and animals.

16. SEXUAL REPRODUCTION Sexual reproduction is a mode of reproduction involving the fusion of haploid female gamete (egg cell) and haploid male gamete (sperm cell) to form a zygote which develops into the adult. But mostly it is a specialized case of nuclear exchange or reorganization in a unicellular eukaryote like protists. It involves meiosis. It may take place in between asexual reproduction

17. TYPES OF SEXUAL REPRODUCTION In the Protists it is of the following type: 1.Syngamy 2.Conjugation 3.Autogamy 4.Endomixis 5.Hemixis 6.Cytogamy 7 . P art h eno g enesis

18. SYNGAMY It is the complete fusion of the whole individual which act as gamonts or gametes. Fused diploid nucleus is known as synkaryon. It may be of the following type: HOLOGAMY : It is the fusion of two mature individuals which do not produce gametes . Seen in some rhizopods and flagellates PAEDOGAMY : It is the fusion of two young individuals which are not mature , fusion of similar gametes is called isogamy and fusion of dissimilar gametes is called anisogamy.

19. CONJUGATION

20. Conjugation in Paramecium

21. Conjugation is the transfer of genetic material between cells by direct cell-to-cell contact or by a bridge-like connection between two cells. Conjugation as a mode of sexual reproduction is seen in some ciliated protozoa. Conjugation is the temporary union of two individuals which mutually exchange micro nuclear material. It is unique type of a sexual process in which two organisms separate soon after exchange of nuclear material. Conjugation does not take place during night or darkness It starts in early morning and continues till afternoon.

22. In conjugation two Paramecium (referred to as pre-conjugant’s ) of the opposite mating types of the same variety come together with their ventral surfaces and unite by their oral grooves; their cilia produce a substance on the surface of the body which causes adhesion of the two conjugating paramecia. They stop feeding and their oral groove apparatus disappears. The pellicle and ectoplasm, at the point of contact, of both break down and a protoplasmic bridge is formed between the two animals. Now, these individuals are called conjugant’s.

23. Macronucleus Changes: Soon after pairing the macronucleus degenerates into fragment and is absorbed in the cytoplasm Micronucleus Changes: Simultaneously the micronucleus undergoes two pre- gametic divisions, of which first is reduction division. As a result four daughter micronuclei are formed each with haploid number of chromosome. Three of the four daughter micronuclei degenerate in each conjugant.

24. The remaining micronucleus of each conjugant divides mitotically into two unequal pronuclei or gametic nuclei forming a larger stationary female pro-nucleus and a smaller, active migratory male pro-nucleus. The migratory male pronucleus of the two conjugant’s are exchanged so that the male pronucleus of one passes into the other through protoplasmic bridge and fuses with the female pronucleus forming the zygote nucleus or synkaryon . The conjugant’s now separate and is called exoconjugant’s . The synkaryon in each conjugant divides thrice and eight nuclei are formed. Four of them enlarge and become macronuclei, while the remaining four are known as micronuclei.

25. Three of the four micronuclei disintegrate. The remaining micronucleus divides and at the same time the ex-conjugant divides by binary fission into two cells, each having two macronuclei and one micronucleus. The cells and their micronuclei divide a second time to form four paramecia from each ex-conjugant, so that each has one macronucleus and one micronucleus Micronucleus divides by mitosis followed by cytokinesis Thus four + four = eight small daughter Paramecia formed from the two exconjugants These grow to retain the adult form.

26. Significance of Conjugation: Rejuvenation : Conjugation serves as a process of rejuvenation and re- organisation by which the vitality of the race is restored. If conjugation does not occur for long periods, the paramecia weaken and die. It has been found that individuals cannot continue to multiply indefinitely by asexual methods. After a definite number of asexual generations the rate of fission declines. Nuclear reorganization: Old and decaying macronucleus is replaced by a new one during conjugation. Heredity variations: The fusion of pronuclear facilitates exchanges of nuclear material.

27. AUTOGAMY Autogamy or self-fertilization, refers to the fusion of two gametes that come from one individual. Described by Diller in 1936. He called it as self fertilization. It takes place in Paramecium aurelia which has one macronucleus and two micronuclei. It involves only one individual. It always leads to homozygosity. It is a special type of nuclear reorganization. It takes place as follows: The macronucleus disintegrates. A temporary protoplasmic cone forms near the cytostome.

28. Both the micronuclei divide by MEIOSIS to produce eight daughter nuclei . Seven of these degenerate and only ONE remains which divide by mitosis to produce two gamete nuclei. These two enter the protoplasmic cone and fuse to form the diploid zygote nucleus. It divides by TWO quick mitosi s to produce FOUR daughter nuclei of which two become large (macronuclei) and two remain small ( micronuclei). The micronuclei divide by mitosis followed by cytokinesis to produce two Paramecia each with a macronucleus and two micronuclei.

29. P R O C E SS O F A U T O G AMY

30. Significance of autogamy As a result of autogamy , a new macronucleus is formed which rejuvenates paramecium by increasing its vitality. It is a type of sexual reproduction in which self-fertilization takes place and homozygous offsprings are produced.

31. ENDOMIXIS Endomixis is a phenomenon of periodic nuclear reorganisation in cells of ciliated protozoans such as Paramecium.   Described by Woodruff Erdmann in 1914. Special method of nuclear reorganisation in Paramecium aurelia. It involves a single individual and is similar to autogamy or hemixis. Four daughter Paramecia are formed , each having one maconucleus and two micronucleus

32. There is no meiosis and no nuclear fusion in this process. It occurs in single individual in the following way: The macronucleus degenerates and disappears. The two micronuclei divide twice by mitosis and produce eight nuclei. Six of these eight degenerate. The Paramecium divides into two. Each daughter Paramecium contains one nucleus. The nucleus divides again twice by mitosis to produce four nuclei. Two nuclei enlarge and become macronuclei and two become micronuclei Each micronucleus and the body of Paramecium divide and produce two daughter Paramecia. Paramecium gets one macronucleus and two micronuclei. At the end of endomixis four daughter Paramecia are produced from a single individual.

33. Significance of endomixis As a result of endomixis a new macronucleus is formed which rejuvenates Paramecium. A single individual produces four daughter individuals.

34. HEMIXIS Hemixis is a reorganization process in various ciliated protozoans in which the macronucleus breaks up and a new macronucleus is reconstituted from the fragments without accompanying micronuclear changes compare endomixis . Described by Diller in Paramecium aurelia . Special type of nuclear reorganisation in a single individual. In this the macronucleus is rejuvenated . Macronucleus gives off chromatin balls which are supposed to consist of redundant or waste materials. Micronuclei divide normally.

35. Hemixis is primarily a process of macro-nuclear fragmentation and division without any unusual micro-nuclear activity. Diller classified hemixis into four types, namely A, B, C, and D as shown in Fig. 20.24   Type A is the simplest form of hemixis characterised by a division of the macronucleus into two or more parts. This division is not synchronized with micro-nuclear division. Type B is characterised by the extrusion of one to 20 or more chromatin balls from the macronucleus into the cytoplasm. Type C is characterised by the simultaneous splitting of the macronucleus into two or more major portions and the extrusion of macro-nuclear balls into cytoplasm .

36. Type D is considered to represent pathologic conditions in which the macronucleus undergoes complete fragmentation into chromatin balls that eventually disappear from the cell. Micronuclei generally disappear before the dissolution of the macronucleus.

37. CYTOGAMY Cytogamy is another type of self-fertilization, two organisms join together but do not undergo nuclear exchange. It was reported by Wichterman(1940) in the small strains of Paramecium caudatum. It involves two Paramecia The process is similar to conjugation but there is no exchange of gametes between the two. Instead , in each the two haploid gamete nuclei fuse to form a diploid synkaryon or zygote nucleus.

38. Generally cytogamy is less frequent . In cytogamy two Paramecia form a pair and become attached at their oral surface as in conjugation. Early nuclear divisions are similar to that of conjugation but there is no nuclear exchange between the individuals called as cytogamonts . Two haploid gamete nuclei in each of the individual, fuse to form a synkaryon . The individuals now separate and divide as in conjugation. Also a new macronucleus is formed as in conjugation . Significance of cytogamy A new macronucleus is formed which rejuvenates  Paramecium Self- fertilization occurs in this process also and completely homozygous offsprings are produced

39. PARTHENOGENESIS Parthenogenesis is a reproductive strategy that involves development of a female (rarely a male) gamete (sex cell) without fertilization.  It takes place in certain Protists in which the gametes fail to fertilize. It is a special type of asexual reproduction. It is the production of offsprings from unfertilized eggs. Eg- Actinophrys