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Biology - Unit 2 Revision
Topic Summary - Classification and Species
Classification DNA Hybridisation Evidence for Genetic Relationships
Species: A group of organisms that are DNA hybridisation is a method to which scientists Genetic relationships can be shown by;
similar to each other but different use to find which species are most closely related - the similarity between the amino acid sequences
from members of other species. to each other (or had a more recent common - how antibodies of one species respond to specific
ancestor). antigens in the blood serum of another
Members of the same species reproduce to - similarity of bases through DNA hybridisation
produce fertile offspring, whilst members of two First, DNA strands are taken from two different
different species reproduce to produce infertile species. These strands are then heated in order Amino acid sequences can be used to show
offspring. to separate them. genetic relationships by investigating the similarity
between the amino acid sequence of the same
Living organisms are classified into groups. The After the strands have been separated, they are protein in different species.
grouping of species is called classification. allowed to cool with a strand of DNA from the
Taxonomy is when the principles of biology are other species. This then encourages the This will indicate how closely the species are re-
used to sort the species. complimentary bases on each of the DNA strands lated and how recent their common ancestor is.
to form hydrogen bonds with each other. This
There is a hierarchical system; Kingdom, only occurs on certain base pairs. Antibodies and antigens can also be used in a
Phylum, Class, Order, Family, Genus and process called immunological comparisons.
Species. Once this bonding has occurred, the DNA strands
are heated again to separate the strands. The This uses antibodies of one species responding to
Species are named in Latin or Greek. The first strands which separate at the highest the specific antigens of another species on
name is the generic name and which genus the temperature are more closely related. This is proteins in the blood serum.
organism belongs. The second name is the because more hydrogen bonds have formed be-
specific name, unique to that species. When this happens precipitate is formed. This
tween the complementary bases. indicates that the higher the number of similar
Phylogeny: The evolutionary relationship Therefore more bases are complimentary with antigens, the more precipitate is formed. If more
between organisms. one another in the two species. Therefore the precipitate is formed then the species are more
higher the temperature for separating the strands, closely related and have a more recent common
Phylogeny reflects the evolutionary branch that ancestor.
led to the organism. This is usually shown in a the more recent the common ancestor is between
tree diagram. This can also help to show the these two species. These three techniques can all give genetic
common ancestors between species. evidence for species being related to one another.