Gene Expression & Phenotype (College Board AP® Biology): Study Guide

Gene expression & phenotype

• The phenotype of a cell or organism is determined by the combination of genes that are expressed and the levels at which they are expressed

  • Expression of different gene combinations allows cells to produce different proteins

  • Altering the level of gene expression allows cells to control how much of a protein is produced

• Altering gene expression is important in the processes of:

  • cell differentiation

  • development

Cell differentiation

• Every nucleus within the stem cells of a multicellular organism contains the same genes

• Despite having identical genomes stem cells can give rise to a diverse range of cell types during differentiation; this is the process by which cells become specialized

  • Under certain conditions, some genes in a stem cell are activated, whilst others are inactivated

  • mRNA is transcribed from active genes only

  • This mRNA is then translated to form proteins

  • These proteins will be specific to the tissue in which the cell is found; they determine the structure of the cell and the processes that occur within it

Development

• The term development in this context refers to the process by which a fertilized egg cell develops into a multicellular organism

• Correct development requires the expression of the right genes, in the the right location, and in the right order

  • This ensures that tissue types and body parts develop in the correct location

• This sequential gene expression is controlled by transcription factors

  • E.g. the Hox genes are a group of genes that code for transcription factors involved in development