Video Transcript
Which of the following is an
assumption scientists make when classifying organisms based on genetic analysis? (A) The more DNA two organisms have
in common, the more recently they shared a common ancestor. (B) The more DNA two organisms have
in common, the less recently they shared a common ancestor. Or (C) organisms have only shared a
common ancestor if they have identical DNA.
In order to answer this question,
we first have to understand that when we classify organisms based on genetic
analysis, we’re grouping them together based on similarities in their DNA or
genes. Organisms that are more closely
related will have more DNA in common. Since you and your siblings share a
more recent common ancestor, your parents, you’ll have more DNA in common than you
would have with your less closely related cousins, who share a less recent common
ancestor, your grandparents.
The same is true when we talk about
classifying organisms. The more recent the common
ancestor, the more DNA two organisms will have in common. Let’s look at an example. Cats, humans, and gorillas are all
members of the same class, which is mammals. However, humans and gorillas share
a more recent common ancestor than the one that they share with cats. Recall our seven taxonomic levels
of classification from most general to most specific. They are kingdom, phylum, class,
order, family, genus, and species.
When we classify organisms based on
genetic analysis, they’ll share a more specific group if they have more DNA in
common. Cats, humans, and gorillas all
belong to the same class, mammal, whereas humans and gorillas both belong to the
same family hominid. They share a more specific
classifications because they share a more recent common ancestor and have more genes
in common.
Now, we’re ready to answer our
question. When classifying organisms based on
genetic analysis, scientists must assume that the more DNA two organisms have in
common, the more recently they shared a common ancestor.
