4.5 Species and taxonomy

What is a species?

A group of organisms that can (interbreed to) produce fertile offspring

Suggest why 2 different species are unable to produce fertile offspring

● Different species have different chromosome numbers → offspring may have odd chromosome number

● So homologous pairs cannot form → meiosis cannot occur to produce gametes

Explain why courtship behaviour is a necessary precursor to successful mating

● Allows recognition of members of same species → so fertile offspring produced

● Allows recognition / attraction of opposite sex

● Stimulates / synchronises mating / production / release of gametes

● Indicates sexual maturity / fertility

● Establishes a pair bond to raise young

Describe a phylogenetic classification system

● Species (attempted to be) arranged into groups, called taxa, based on their evolutionary origins (common ancestors) and relationships

● Uses a hierarchy:

○ Smaller groups are placed within larger groups

○ No overlap between groups

Name the taxa in the hierarchy of classification

1. Domain (largest / broadest)

2. Kingdom

3. Phylum

4. Class

5. Order

6. Family

7. Genus

8. Species (smallest)

How is each species universally identified?

A binomial consisting of the name of its genus and species, eg. Homo sapiens

Suggest an advantage of binomial naming

Universal so no confusion as many organisms have more than one common name.

How can phylogenetic trees be interpreted?

● Branch point = common ancestor

● Branch = evolutionary path

● If two species have a more recent common ancestor, they are more closely related (eg. C & D)

Describe two advances that have helped to clarify evolutionary

relationships between organisms

1. Advances in genomesequencing → allowing

comparison of DNA base sequences

● More differences in DNA base sequences → more distantly related / earlier common ancestor

● As mutations (change in DNA base sequences) build up over time

2. Advances in immunology → allowing comparison of protein

tertiary structure (eg. albumin)

● Higher amount of protein from one species binds to antibody against the same protein from another species → more closely related / more recent common ancestor

● As indicates a similar amino acid sequence and tertiary structure

● So less time for mutations to build up