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

Describe 5 ways in which Courtship Behaviour ensures successful reproduction

1. Recognising members of the same species

2. Identifying a mate that is capable of breeding

3. Forming a pair bond

4. Synchronisation of mating

5. Become able to breed
   

Explain Recognising members of the same species

• To ensure that mating occurs only between members of the same species

• Only members of the same species will produce fertile offspring

• This prevents interbreeding, making reproduction more successful

• Due to this specificity, it can be used when classifying organisms

Explain Identifying a mate that is capable of breeding

• Both partners need to be sexually mature, fertile and receptive to mating

Explain Forming a pair bond

• Leading to successful mating and raising of offspring

• Stable family

Explain Synchronisation of mating

Ensuring that mating occurs when there’s the max probability of the sperm and egg meeting

Explain Becoming able to breed

by bringing a member of the opposite sex into a physiological state that allows breeding to occur

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) - Bacteria, Archaea and Eukarya

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 genome sequencing → allowing comparison of DNA base sequences.

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

   • As mutations build up over time

2. Advances in immunology → allowing comparison of protein tertiary structure.

   • 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