Symmetry in Biology By Ashlen Mezrahi Radial Symmetry

Symmetry in Biology By Ashlen Mezrahi

Radial Symmetry: Characteristics ● Taxon Radiata - polyphyletic assemblage of different phyla of the Animal kingdom ● Top and bottom ● Mouth ● No head ● No rear

Radial Symmetry: Jellyfish C 4 v D 4

Special Case: Echinodermata ● Starfish, sea urchins, and sand dollars ● Bilateral symmetry at the larval stage ● Fivefold symmetry as adults ○ Pentamerism ○ Five parts; 72° apart Larval Stage: C 2 v

Fivefold symmetry in Echinodermata (C 5 v)

Bilateral Symmetry ● 99% of animals ● Mirror image; left and right side ○ Sagittal Plane ● Internal organs asymmetrical ● Evolved trait over 500 million years ago C 1 v

Bilateral Symmetry: Evolutionary importance ● Forward Movement ○ Seeking food, shelter, home, and reproductive mates ○ Active, directed movement requires an elongated body form with head (anterior) and tail (posterior) ends ● Development of a head and the concentration of sensory organs

Bilateral Symmetry (C 1 v)

Symmetry = Fitness ● Symmetrical Faces “more attractive” ○ Healthier; genetically fitter ■ Asymmetry: depression, anxiety, headaches and even stomach problems ○ Easier for the brain to recognize ● Experiments with birds and insects revealed that females prefer to mate with males possessing the most symmetrical sexual ornaments ○ Female barn swallows prefer males with long, symmetrical tail feathers

Facial Symmetry: Average Example

Very Symmetrical Face

Many more complicated symmetrical shapes in nature! Example- Platonic Solid: Icosahedron 2) Clorophyll protein of a pea 3) Circogonia Icosahedra Radiolaria 4) Radilarian organism 5) Aids virus

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