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Origin & Evolution of Sex in Algae

The document discusses the origin and evolution of sexual reproduction in algae, highlighting that while most primitive algae reproduce asexually, sexual reproduction supplements this method and enhances evolutionary speed. It details various forms of sexual reproduction such as hologamy, isogamy, and oogamy, and suggests that sexual reproduction likely originated from the accidental fusion of motile zoospores under unfavorable conditions. The evolution of sex in algae involves the differentiation of gametes and sex organs, occurring independently across different algae lineages.

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729 views2 pages

Origin & Evolution of Sex in Algae

The document discusses the origin and evolution of sexual reproduction in algae, highlighting that while most primitive algae reproduce asexually, sexual reproduction supplements this method and enhances evolutionary speed. It details various forms of sexual reproduction such as hologamy, isogamy, and oogamy, and suggests that sexual reproduction likely originated from the accidental fusion of motile zoospores under unfavorable conditions. The evolution of sex in algae involves the differentiation of gametes and sex organs, occurring independently across different algae lineages.

Uploaded by

trivedideepali1294
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Origin & Evolution of Sex in Algae

Origin of Sex

• Almost all Eukaryotic plants reproduce asexually and sexually

• Sexual reproduction requires union of two special cells- the gametes

• Gametes alone can not form new plant

• Most primitive algae- Cyanophyceae do not show sexual reproduction and reproduce by cell
fission

• Protococcus of Chlorophyceae

reproduce by cell fission

• Other algae reproduce by sexual method which does not replace asexual method but
supplement it

• Sexual reproduction increase speed of evolution

• Gametes were derived from the motile zoospores

• Ex. Chlamydomonas debaryanum

• 3 divisions in cell- 8 zoospores

• 4 divisions in cell- 16 gametes

• Ex. Ulothrix zonata

• 2 divisions in cell- 4 macrozoospores

• 3 divisions in cell- 8 microzoospores

• 4 divisions in cell- 16 microzoospores

• 5/6 divisions in cell- 32/ 64 gametes

• The similarity of gametes to zoospores suggests that sex (union of two cells) has originated
by the accidental fusion of zoospores which had become too small to form a new plant
alone. The fusion probably took place in response to certain unfavorable environmental
conditions. Since this accidental fusion proved of advantage to all the plants in form of
increased vitality and vigor the method was maintained and finally fixed.

• Sexual reproduction in the lower organisms is always associated with conditions unfavorable
for growth

• Parthenogametes of Ulva mutabilis


Evolution of Sex in Algae

• Hologamy

– Chlamydomonas, Dunalliela salina

• Isogamy

– Chlamydomonas, Cladophora, Ectocarpus, Spirogyra

• Functional/ Physiological Anisogamy

– Ulothrix, Spirogyra

• Anisogamy

– Chlamydomonas braunii, Pandorina

• Primitive Oogamy/ Heterogamy

– Chlamydomonas coccifera, Eudorina

• Oogamy

– Sargassum, Fucus

– Oedogonim

– Chara

• Evolution of sex involves:

– Differentiation of gametes

– Differentiation of sex organs

– Restriction of motility and increased nutrition in female gamete

• Evolution of sex in algae has taken place in several independent lines

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