Here are two methods scientists use to establish how closely related individuals
are to each other.
Comparison of similar proteins between species.
Since the sequence of a protein is determined by
the DNA sequence, comparison of key proteins in different
individuals allows a portion of the DNA sequence of the organisms
to be compared. Clearly, only a tiny fraction of the total number
of proteins can be studied.
Differences in the number of
chromosomes between closely related species.
Especially in plants, the characteristic number
of chromosomes in
a species can be different from the chromosome number in a closely
related species. Changes in chromosome number usually occur by
duplication of all the chromosomes at once but can
sometimes occur by duplication of one or a few chromosomes.