Dollo’s law:  A biological generalization positing that complex characters, once lost in evolution, are extremely unlikely to reappear and thus the loss of complex characters is virtually always irreversible.

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#Id: 535

#Unit 2. Cellular Organization

We use the principle of parsimony in comparing the organization of orthologous genes by assuming that a common feature predates the evolutionary separation of the two species.

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#Id: 536

#Unit 2. Cellular Organization

Surface area/volume ratio of bacteria is high compared to the same ratio for larger organisms of similar shape.

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#Id: 537

#Unit 2. Cellular Organization

The shape of a bacterium is governed by its rigid cell wall.

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#Id: 538

#Unit 2. Cellular Organization

Some bacterial species are pleomorphic. Example: genera Arthrobacter, Corynebacterium, Mycobacterium, Mycoplasma, etc.

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#Id: 539

#Unit 2. Cellular Organization

Helical bacteria with: 

1. Less than one turn- vibrioid shape

2. Complete turn- helical shape

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#Id: 540

#Unit 2. Cellular Organization

Protein filaments in cytoplasm are responsible for the rod and helical cell shapes of bacteria.