1.2 

Concepts and Uses of the Classification System

Biological Classification System

●     Organisms are classified into groups based on the features that they share

●     Aims to reflect evolutionary relationships

●     The smallest group of classification is species.

Species:

 A group of organisms that can reproduce to produce fertile offspring

Binomial Naming System

●     Naming species using an internationally agreed-upon system

●     The scientific name is made of two parts: genus and species.

●     Rules:

○ The genus name starts with a capital letter.

○ The species name is all lowercase.

○ Genus comes before species.

○ If typed: use italics.

○ If handwritten, underline to show italics.

Example: Pavo cristatus

 (Pavo = genus, cristatus = species)

Classification Tools + Taxonomy

●     Keys: Used to classify organisms using external features

●     Dichotomous Key: Identifies organisms based on observable features

Order of Classification (out of syllabus)

DOMAIN (largest)

      ↓

KINGDOM

      ↓ 

PHYLUM

      ↓ 

CLASS

     ↓ 

ORDER

     ↓ 

FAMILY

     ↓  

GENUS

     ↓ 

SPECIES (smallest)

The more levels two organisms share, the more closely related they are genetically.

DNA Sequencing & Evolutionary Relationships

● DNA Sequencing:

 The sequence of bases (A, T, C, G) in DNA is used to compare organisms.

○ The more different two sequences are, the less closely related the organisms.s

○ Organisms sharing DNA with a recent common ancestor are more closely related.

Example:

 Organisms with a common ancestor from 3 million years ago are more closely related to each other than those from 200 million years ago.

Written by Sahana Venkat