4.5 Species and taxonomy

What is a species?

• A group of organisms that can interbreed to produce fertile offspring.

Why are two different species unable to produce fertile offspring?

• Different species have different chromosome numbers, so their offspring may have an odd chromosome number.

• Therefore, homologous pairs cannot form, meaning meiosis cannot occur to produce gametes.

Why is courtship behaviour necessary for successful mating in terms of species recognition?

• Courtship allows recognition of members of the same species, so that fertile offspring are produced.

Why is courtship behaviour necessary for successful mating in terms of attracting a mate?

• Courtship allows recognition and attraction of the opposite sex.

Why is courtship behaviour necessary for successful mating in terms of gametes?

• Courtship stimulates and synchronises mating, and the release of gametes.

Why is courtship behaviour necessary for successful mating in terms of maturity and pair bonding?

• Courtship indicates sexual maturity and fertility.

• It also establishes a pair bond to raise young.

How are species arranged in a phylogenetic classification system?

• Species are arranged into groups called taxa based on their evolutionary origins (common ancestors) and relationships.

What two features describe the hierarchy used in phylogenetic classification?

• Smaller groups are placed within larger groups.

• There is no overlap between groups.

What are the eight taxa in the hierarchy of classification, from largest to smallest?

• Domain (largest/broadest)

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species (smallest)

How is each species universally identified?

• By a binomial consisting of the name of its genus and its species, for example Homo sapiens.

What is an advantage of binomial naming?

• It is universal, so there is no confusion, as many organisms have more than one common name.

On a phylogenetic tree, what does a branch point represent?

• A branch point represents a common ancestor.

On a phylogenetic tree, what does a branch represent?

• A branch represents an evolutionary path.

On a phylogenetic tree, how can you tell that two species are more closely related?

• If two species have a more recent common ancestor, they are more closely related (for example, species C and D).

What two technologies have helped to clarify evolutionary relationships between organisms?

• Genome sequencing.

• Immunology.

How have advances in genome sequencing helped to clarify evolutionary relationships between organisms?

• Advances in genome sequencing allows the comparison of DNA base sequences between organisms.

How have advances in immunology helped to clarify evolutionary relationships between organisms?

• Advances in immunology allow the comparison of protein tertiary structure between organisms, for example using albumin.

What does a greater number of differences in DNA base sequences between two species indicate about their evolutionary relationship?

• More differences in DNA base sequences means the species are more distantly related or have an earlier common ancestor.

• This is because many mutations have accumulated since they shared a common ancestor.

• Mutations build up over time.

In an immunological comparison, what does a higher amount of protein from one species binding to an antibody against the same protein from another species indicate?

• It indicates the species are more closely related and have a more recent common ancestor.

• This is because a similar amino acid sequence (between the two species' proteins) and a similar tertiary structure indicate that fewer mutations have accumulated since they shared a common ancestor.