Genetic information, variation and biodiversity: every key term you need (+ practice quiz)

Nucleotide

A phosphate group, a pentose sugar and a nitrogenous base. Joined by phosphodiester bonds into the sugar-phosphate backbone.

Semi-conservative replication

Each new DNA molecule keeps one original strand and one newly built strand — confirmed by the Meselson and Stahl density experiment.

DNA helicase

Unwinds the double helix and breaks the hydrogen bonds between complementary bases, exposing each strand as a template.

Genetic code features

Universal, non-overlapping and degenerate: most amino acids have more than one triplet, so some base substitutions change nothing.

Intron

A non-coding section of a gene, transcribed into pre-mRNA then spliced out before translation. Absent from prokaryotic genes.

Transcription

RNA polymerase builds a complementary pre-mRNA copy of the template strand, which is then spliced into mature mRNA.

Translation

Ribosomes read mRNA codons while tRNA delivers matching amino acids by anticodon pairing, forming a polypeptide.

Gene mutation

A change in the DNA base sequence. Substitutions may be silent; insertions and deletions cause a frame shift affecting every later codon.

Species

A group of organisms with similar characteristics that can interbreed to produce fertile offspring.

Courtship behaviour

Species-specific signalling that lets individuals recognise a mate of the same species, assess fertility and form a pair bond.

Phylogenetic classification

Groups organisms by evolutionary relationship and shared ancestry, rather than by superficial physical resemblance.

Species richness vs index of diversity

Richness counts species present; the index also accounts for how many individuals each species has, so it reflects dominance.

Standard deviation

Measures spread around a mean. Overlapping error bars suggest a difference between samples may not be significant.

Student's t-test

Tests whether the means of two samples differ significantly. Compare the calculated value with the critical value at p = 0.05.

Correlation coefficient

Measures the strength and direction of a linear relationship between two variables. Correlation alone never establishes cause.

Random sampling

Using random coordinates to place quadrats removes investigator bias, so the sample is more likely to represent the whole area.

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