Classification Systems and Species Concepts

This page delves into classification methods and the definition of species, which are crucial topics in module 4 OCR A level biology.

Classification is the process of organizing organisms into groups. Hierarchical classification divides organisms into increasingly specific categories: domain, kingdom, phylum, class, order, family, genus, and species.

Example: The binomial naming system uses the genus and species names to identify organisms, such as Felix tigris for tigers.

A species is defined as a group of individuals with similar characteristics that can interbreed to produce fertile offspring. Offspring from different species are typically infertile due to chromosome number mismatches.

Highlight: Mules, the offspring of horses and donkeys, are infertile because they have an odd number of chromosomes (63) that prevents proper meiosis.

Phylogenetic classification is based on evolutionary relationships, considering how closely related different species are and how recently they shared a common ancestor.

Definition: Phylogenetic classification organizes species based on their evolutionary relationships and common ancestry.

Three methods for comparing relationships between species are:

1. DNA Hybridization
2. Amino Acid Sequence Comparison
3. Protein Shape Comparison

Vocabulary: DNA hybridization involves comparing the base sequences of DNA from different species to determine their genetic similarity.

Evolutionary Relationships and Variation

This page focuses on methods for determining phylogenetic classification evolutionary relationships and understanding variation within and between species.

DNA Hybridization is a technique used to compare the genetic similarity between species. It involves labeling DNA from one species, mixing it with DNA from another species, and measuring the temperature required to separate the hybrid DNA strands.

Highlight: A higher temperature required to separate hybrid DNA indicates more hydrogen bonds, more complementary base pairing, and thus more closely related species.

Amino Acid Sequence Comparison involves analyzing the sequence of amino acids in the same protein across different species. This method is less informative than DNA sequence comparison because it doesn't provide information on introns and the genetic code is degenerate.

Protein Shape Comparison uses immunological techniques to compare the shape of the same protein in different species. This method involves creating antibodies against a protein from one species and testing their reaction with the same protein from another species.

Example: Antibodies created against albumin from Species A are used to test the similarity of albumin in Species B. More precipitate formation indicates more similar protein shapes and more closely related species.

Variation refers to differences in characteristics between organisms and can be classified as:

• Intraspecific: differences within the same species
• Interspecific: differences between different species

Definition: Intraspecific variation refers to differences between organisms of the same species, while interspecific variation refers to differences between organisms of different species.

Causes of variation include both genetic and environmental factors.