Analogous characters

Analogous characters - which are which, and 2) deciding...

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Analogous characters = homoplasious characters: two characters not sharing a common genetic and developmental history and usually attained by adaptation to a similar ecological or functional challenge. Bats and Birds forelimbs and wings: they arehomologous as forelimbs, but analogous as wings (a simple but crucial distinction). Analogous characters are attained by convergent evolution where descendants resemble each other more than they do their respective ancestors. Ichthyosaur, Fish, Porpoise; desert plants. Parallel evolution e.g. marsupials (M) and placentals (P). Ancestors are viewed as different but related. Point is: two possible evolutionary trees could be drawn: (P,M) (P,M) (P,M) (P,M) or (M,M,M,M) (P,P,P,P) If the characters that a set of organisms have could be either analogous or homologous characters, the systematist is faced with several problems: 1) attempting to identify
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Unformatted text preview: which are which, and 2) deciding whether (or how) to perform character weighting . Excluding characters is an extreme form of weighting (weight = 0). Placentals have a placenta, marsupials a pouch where the immature young finish their development. These are major characters, should they carry more weight in our assignment of relationship. If we looked for other characters in the animals we could probably find many that would link the dog-dog, squirrel-squirrel, cat-cat, anteater-anteater, etc. Since characters are the data we will use to do systematics other questions arise: 1) should we use single or many characters?, 2) what are legitimate characters (morphology, ecology, etc.)? 3) how do we weight those that are chosen?...
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This note was uploaded on 11/06/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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