Influence of Genetic Variants on Phenotype (OCR GCSE Biology A (Gateway))

Gene Expression

Higher Tier Only

• The human genome contains all of the genetic information that an organism requires to function

• This includes sections of DNA which are called coding DNA and non-coding DNA

• Coding and non-coding DNA both play a role in gene expression

Coding DNA

• Coding DNA refers to the genes of an organism which provide the instructions required to synthesize proteins

• Only a small proportion of the genes in the genome may be expressed at any time

• This is because genes must be activated if they are to be expressed

Non-coding DNA

• Non-coding DNA does not code for proteins

• However, it can influence protein synthesis through interactions with the coding regions of DNA

• Non-coding DNA can cause activation or deactivation of genes in the coding DNA

DNA is made up of regions of coding DNA and regions of non-coding DNA, both regions are involved in gene expression

Mutations and gene expression

• Some genetic variants (resulting from mutation) can influence the phenotype of the organism

• Variants which directly impact gene expression work by

  • Altering the DNA base sequence within the coding DNA regions of the genome

  • The mutation significantly alters the structure of the protein produced

  • This results in a non-functional protein

    • For example, an enzyme active site may be altered significantly so that the substrate no longer fits

• Variants which indirectly impact gene expression work by

  • Altering the DNA base sequence within the non-coding DNA regions of the genome

  • This mutation can have two effects on the coding DNA

    • It may activate genes in the coding regions resulting in transcription of a gene which was previously not being expressed

      • A protein is produced

    • It may inactivate genes in the coding regions which halts transcription of a gene which was previously being expressed

      • A protein isn't produced

Gene expression can be affected directly and indirectly by mutations within the coding and non-coding DNA