D.2.2 Gene Expression

phenotype

observable traits of an organism resulting from genotype and environmental factors

transcription factor

a protein that binds to specific DNA sequences to control the transcription of mRNA

enhancer

regulatory sequences on the DNA which increase the rate of transcription when activator proteins bind to them

epigenesis

the development of patterns of differentiation in the cells of a multicellular organism

epigenetics

the study of heritable changes in gene activity that are not caused by changes in the DNA base sequences; mechanisms that produce such changes are DNA methylation and histone modification

genotype

the combination of alleles inherited by an organism

transcriptome

the range of mRNA transcripts produced in a specific cell or tissue type at a particular time

methylation

the reversible addition of a methyl group (-CH3) within chromatin

epigenetic tag

chemical tags (such as methyl or acetyl groups) that are added directly to DNA or onto histone proteins to regulate gene expression, blocking or allowing access to a gene’s ‘on’ switch

epigenetic inheritance

an inheritance pattern in which a modification to chromatin alters gene expression in an organism; a parent’s experiences, in the form of epigenetic tags, can be passed down to offspring

imprinting

process by which only one copy of a gene in an individual (either from their mother or father) is expressed, while the other copy is suppressed; gene expression is silenced by the epigenetic addition of chemical tags to the DNA during egg or sperm formation

monozygotic twins

identical twins result from the fertilization of a single egg by a single sperm, with the fertilized egg then splitting into two; identical twins share the same genomes and are always of the same sex

monozygotic

derived from a single ovum and so genetically identical

operon

sequence of adjacent bacterial genes all under the transcriptional control of the same operator

operator

a DNA region at one end of an operon that acts as the binding site for a repressor protein; when the operator is complexed with the repressor, transcription is prevented

LAC operon

an inducible operon including three loci involved in the uptake and breakdown of lactose in the bacterium e-coli

repressor

the protein product of a regulator gene that acts to control transcription of an operon; the repressor binds to the operator and prevents transcription by RNA polymerase of an operon

inducer

a molecule that is capable of activating the transcription of a gene by combining with and inactivating a genetic repressor