Evidence used in classification

Evidence used in classification. Human Biology Unit 2, Topic 9.2

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EVIDENCE USED IN CLASSIFICATION
Biochemical Evidence
Although live on earth is diverse, all living organisms are made up of the same basic
molecules.
Scientists have developed techniques to compare these molecules in order compare these
molecules in more detail > USUALLY INVOLVES STUDYING PROTEINS AND DNA.
CYTOCHROME C
One protein, called cytochrome c, has been studied in detail.
It is found in mitochondria and is important for cellular respiration.
Cytochrome c contains 140 amino acids in Chordates and slightly more in other organisms.
Scientists have found that cytochrome c has changed very little over millions of years of
evolution
E.g. the monkeys and humans split off from a common ancestor 20 million years ago, yet
there is only 1 amino acid difference in their cytochrome c.
DNA HYBRIDISATION
DNA is taken from two different organisms and the DNA is `unzipped' and then mixed
together.
Therefore, if they have complementary base pairs they will match up > THIS IS KNOWN AS
HYBRIDISATION.
Lot of Hybridisation = Lots of similarities
BUT... How can they tell how much hybridisation has occurred? : Scientists slowly heat up the
hybrid DNA molecules and the more heat that is needed to separate them the more matches
there are.
Anatomical Evidence
Organisms with similar anatomy are believed to be more closely related.
Humans are classified in the order PRIMATES because they have anatomical features that they share
with other primates:
o Grasping limbs with the opposable thumb.
o Brachination (arm can swing through 180 degrees).
o Large brain with developed central cortex to learn skills.
o Forward facing eyes (can judge distance accurately).
o Nails (protection).
Embryological Evidence
Many embryos look the same at the start of the embryo's development and it is only at later stages
they began to look different.

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E.G. all vertebrates have a tail-like structure in early development, but only some of them have tails
later. THIS IS EVIDENCE THEY HAVE EVOLVED FROM A COMMON ANCESTOR.
Immunological Evidence
Proteins act as antigens and recognise can recognise cells as foreign bodies to stimulate an immune
response.
Human serum can be injected into rabbits where the rabbit responds by producing
antibodies specific to the human serum proteins.…read more

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