Nucleic acids (RNA and DNA) are polymers formed when nucleotides join by phosphodiester bonds.  Nucleotides have three components: a phosphate group, a pentose sugar and a nitrogenous base. 

DNA undergoes semi-conservative replication.  During replication, errors may occur through transition, transversion or strand slippage.  Both transition and transversion lead to single nucleotide polymorphisms (SNPs). 

Protein synthesis is a multi-stage process (transcription; splicing; amino acid activation; translation; post-translational modification) requiring both DNA and RNA.  DNA is the molecular code which determines the types and sequence of amino acids within a protein.  RNA is crucial to the assembly of proteins. 

The cell cycle is a multi-stage process during which the cell increases in size (G1), replicates its DNA (S), prepares to divide (G2) and then divides (M).  The cell cycle is regulated by cyclin-dependent kinases (CDKs) and negative regulatory molecules, whose actions create three main checkpoints in the cell cycle: G1 (restriction) checkpoint; G2 checkpoint and metaphase checkpoint. 

During mitotic cell division, which can be subdivided into prophase, metaphase, anaphase and telophase, identical copies of genes are passed to diploid (2n) daughter cells. 

Daughter cells formed during meiosis, which takes place during gametogenesis, are not genetically identical and are haploid (n).  Meiosis, which is also known as reduction division, has two main phases: meiosis I (reduction) and meiosis II (division).  In humans, spermatogenesis takes place in the testes and oogenesis takes place in the ovaries.  Haploid (n) gametes fuse during fertilisation to form a diploid (2n) zygote.  

Genetic information is passed to the next generation in the form of alleles, which are variant forms of genes.  Inheriting two identical alleles leads to a homozygous genotype whereas inheriting different alleles leads to a heterozygous genotype.  The resulting phenotype depends on whether alleles are dominant, codominant or recessive.   The Chi-squared test can be used to assess whether the observed outcome of a genetic cross matches the expected ratio. 

The genome is the genetic information of an organism.  The genome includes coding (exons) and non-coding (introns and intergenic DNA) regions, as well as mitochondrial DNA.  Genomes can be modified using gene technologies; products of genetically modified organisms (GMOs) are used in medicine, agriculture and industry.