Genetic Information, Variation and Relationships- Biology

Comprehensive vocabulary flashcards covering Topic 4 of A-level Biology, including genetic code, protein synthesis, meiosis, mutations, and biodiversity.

Gene

A base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA (including ribosomal RNA and tRNAs).

Locus

The fixed position of a particular gene on a DNA molecule.

Allele

A different version of the same gene.

Chromosome

A threadlike structure composed of tightly coiled DNA wrapped around histones in a eukaryotic cell.

Homologous chromosome

A pair of chromosomes that have the same genes and are therefore the same size.

Eukaryotic DNA

Long and linear DNA stored as chromosomes inside the nucleus, tightly coiled and wrapped around proteins called histones.

Prokaryotic DNA

DNA molecules that are shorter and circular, and are not wound around histones.

Codon

A sequence of three bases on mRNA that codes for a specific amino acid.

Start codon

3 bases at the start of an mRNA sequence which help to initiate translation.

Stop codon

3 bases at the end of an mRNA molecule that do not code for an amino acid, causing ribosomes to detach and stopping translation.

Triplet code

A sequence of three DNA bases that codes for a specific amino acid.

Degenerate Code

A property of the genetic code where each amino acid is coded for by more than one triplet of bases.

Universal Code

A property of the genetic code where the same triplet of DNA bases codes for the same amino acid in all organisms.

Non-overlapping Code

A property of the genetic code where each base in a gene is only part of one triplet of bases, meaning each codon is read as a discrete unit.

Introns

Non-coding sequences of DNA bases within a gene.

Exons

Sequences of DNA bases within genes that code for sequences of amino acids.

Splicing

A post-transcription modification where introns are removed from the RNA sequence.

Genome

The complete set of genes in a cell.

Proteome

The full range of proteins that a cell is able to produce.

Anticodon

3 bases on tRNA which are complementary to the 3 bases in a codon on mRNA.

mRNA structure

Single-stranded, linear molecule made up of codons that acts as a copy of one gene.

tRNA structure

Single-stranded molecule folded into a cloverleaf shape held by hydrogen bonds, containing an anticodon and an amino acid binding site.

Transcription

The first stage in protein synthesis, occurring in the nucleus, where one gene in DNA is copied into mRNA.

Translation

The second stage in protein synthesis, occurring on ribosomes in the cytoplasm, where a polypeptide chain is created using mRNA and tRNA.

RNA polymerase

The enzyme that joins adjacent RNA nucleotides together forming a phosphodiester bond during transcription.

Pre-mRNA

mRNA in eukaryotes that still contains introns before modification.

Spliceosome

A protein used in eukaryotes to remove introns from pre-mRNA.

Haploid

A cell containing one copy of each chromosome, denoted as $(n)$.

Diploid

A cell containing two copies of each chromosome, denoted as $(2n)$.

Meiosis

Cell division involving two nuclear divisions that creates four genetically different haploid daughter cells (gametes).

Independent segregation

The process in meiosis where homologous pairs randomly line up at the equator, creating large numbers of possible chromosome combinations.

Crossing over

The process where non-sister chromatids of homologous pairs twist and exchange parts during meiosis 1, resulting in new combinations of alleles.

Gametes

Sex cells (sperm and egg).

Deletion mutation

A gene mutation where a DNA base is removed, causing a frameshift.

Frameshift

A change in all subsequent triplets of bases caused by the removal of a base, shifting the reading frame back one position.

Substitution mutation

A gene mutation where a DNA base is swapped for a different one.

Nondisjunction

A chromosome mutation where chromosomes or chromatids do not separate equally during anaphase.

Polyploidy

Changes in whole sets of chromosomes, such as Triploid $(3N)$ or Tetraploid $(4N)$, occurring mainly in plants.

Aneuploidy

A change in the number of individual chromosomes, such as having three copies of chromosome 21.

Non-coding DNA (in eukaryotes)

Nuclear DNA found between genes that includes multiple repeats of base sequences and does not code for polypeptides.

Genetic diversity

The number of different alleles in a population, enabling natural selection.

Natural selection

The process leading to evolution where advantageous alleles result in increased reproductive success and increased allele frequency.

Gene pool

All the genes and alleles in a population at a particular time.

Allele frequency

The proportion of organisms within a population carrying a particular allele for a gene.

Evolution

The change in allele frequency over many generations in a population.

Selection pressure

Factors that affect the survival of an organism and drive natural selection.

Directional selection

Selection where one extreme trait provides an advantage, often during environmental change, shifting the modal trait.

Stabilising selection

Selection where the median trait provides the advantage, losing extreme traits over time and decreasing range.

Species

A group of similar organisms that can breed to make fertile offspring.

Binomial system

A universal naming system where individuals are named after their genus and species (e.g., Homo sapiens).

Courtship behaviour

Unique sequences of behaviors animals use to attract a mate, essential for recognizing members of the same species and synchronizing mating.

Hierarchy

A system where smaller groups are arranged within larger groups with no overlap between groups.

Phylogenetic classification

Arranging species into groups based on their evolutionary origins and relationships using a non-overlapping hierarchy.

Taxon

The term for each group in the classification system.

Linnaeus Taxa

The hierarchical groups: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Species richness

The number of different species in a particular community at the same time.

Index of diversity

A measure of species diversity calculated by $D = \frac{N(N-1)}{\sum n(n-1)}$ where $N$ is the total organisms and $n$ is the population size of one species.

Community

All the species in a particular area at a particular time.

Environment

The abiotic (non-living) factors in an area.

Habitat

The range of physical, biological, and environmental factors in which a species can live.

Organelle DNA (Chloroplasts/Mitochondria)

DNA that is short, circular, and not associated with proteins, similar to prokaryotic DNA.

Mutagenic agent

Agents such as ionising radiation and carcinogens that can increase the rate of gene mutation.