Symmetry in Biology By Ashlen Mezrahi Symmetry in biology is the balanced distribution of duplicate body parts or shapes within the body of an organism. In nature and biology, symmetry is always approximate; they are never perfectly symmetrical There are many different classes of symmetry in nature, as body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical. The importance of symmetry in nature

Radial Symmetry: Characteristics Taxon Radiata - polyphyletic assemblage of different phyla of the Animal kingdom Top and bottom Mouth No head No rear No left and right side The organism looks like a pie. This pie can be cut up into roughly identical pieces. Polyphyletic: a set of organisms, or other evolving elements, that have been grouped together but do not share an immediate common ancestor.

Radial Symmetry: Jellyfish C4v Four rotations of 90 degrees

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: C2v

Fivefold symmetry in Echinodermata (C5v)

Bilateral Symmetry 99% of animals Mirror image; left and right side Sagittal Plane Internal organs asymmetrical Evolved trait over 500 million years ago C1v There is an axis; on both sides of the axis the organism looks roughly the same

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 (C1v)

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 Symmetry = Fitness

Facial Symmetry: Average Example

Very Symmetrical Face

Many more complicated symmetrical shapes in nature 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 In geometry, an icosahedron is a polyhedron with 20 faces. 3)circogonia icosahedra radiolaria (a single cell organism living in water)

Sources https://www.livescience.com/4002-symmetry-nature-fundamental-fact-human-bias.html https://simple.wikipedia.org/wiki/Symmetry_(biology) https://en.wikipedia.org/wiki/Symmetry_in_biology https://en.wikipedia.org/wiki/Radiata http://study.com/academy/lesson/types-of-symmetry-in-animals.html https://www.pinterest.com/pin/557109416380865419 http://jwilson.coe.uga.edu/EMT668/EMAT6680.2002.Fall/Nazarewicz/7210_final_2/7210_Project/ https://quizlet.com/14788158/ab-2-flash-cards/