Genetics and Gene Expression

Gene Definition and Function

• A gene is a sequence of nucleotides in DNA that encodes the synthesis of a gene product, either RNA or protein.
• During gene expression, DNA is transcribed into RNA, which can be directly functional or be the intermediate template for a protein that performs a function.

Gene Expression and Inheritance

• The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic traits.
• Genotypes, along with environmental and developmental factors, determine the phenotypes.

Gene Expression in Cells

• Only a fraction of genes are expressed in a cell at any given time.
• Gene products are present in varying amounts, with some being abundant and others being scarce.
• Requirements for gene products change over time.

Types of Gene Expression

• Constitutive gene expression: unvarying expression of a gene, independent of external factors or signals.
• Genes that specify cellular components performing housekeeping functions (e.g. ribosomal RNAs and proteins involved in protein synthesis) are expressed constitutively.
• Genes for products required at all times (e.g. enzymes of central metabolic pathways) are expressed at a constant level in virtually every cell of a species or organism.