Concept And Uses Of Classification Systems

Organisms are classified into groups by the features that they share.

Classification systems aim to reflect evolutionary relationships, and organisms that share more features are thought to share a more recent common ancestor.

Species is a group of organisms that can reproduce to produce fertile offspring.

A horse and a donkey produce offspring called a mule that is infertile, and organisms of the same species must be able to produce fertile offspring together.

The binomial system is an internationally agreed system in which the scientific name of an organism is made up of two parts, the first part being the genus and the second part being the species.

It is internationally agreed and understood, so scientists worldwide can identify the same organism without confusion caused by different common names.

A dichotomous key is a series of paired questions based on observable features that is used to identify organisms.

Each step of the key must offer exactly two choices based on observable features of the organisms.

Vague features such as "large" are subjective and could be interpreted differently by different users, whereas precise features such as "has six legs" ensure the organism is correctly identified every time.

The sequences of bases in the DNA of different organisms can be compared, and organisms with more similar base sequences are considered to be more closely related and to share a more recent common ancestor.

Closely related species share a more recent common ancestor, so there has been less time for mutations to occur and change the base sequence, whereas distantly related species diverged longer ago and have therefore accumulated more differences in their DNA.

Physical features can appear similar because of adaptation to similar environments rather than shared ancestry, whereas DNA base sequences provide direct evidence of the genetic and evolutionary relationships between organisms.