1. 01/07/13 Wiki - Glossary | Epigenetic Control of Gene Expression
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Glossary
Glossary
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Adenosine Triphosphate
(ATP)
A compound that carries energy in a cell. Hydrolysing the phosphate bond in ATP releases energy that can drive
cellular reactions.
Allele Alternative version of a gene.
Autosome A chromosome that is not involved in sex determination. Diploid human cells have 44 autosomes.
Barr body
Densly staining mass of inactive X chromosome at the nuclear periphery of female but not male interphase
nuclei
Bisulfite sequencing
A technique used to differentiate C from meC involving the bisulfite chemical conversion of DNA followed by
amplification and sequencing of the products.
Blastocyst
An early stage of embryo development prior to implantation, consisting of an outer trophoblast layer, an
inner cell mass and a fluid-filled cavity.
Boundary element An element in DNA that limits the spreading of heterochromatin.
Central dogma
A description of the flow of genetic information: DNA is transcribed to RNA which is then translated to
protein.
Centromere The central region in a chromosome.
Chromatin A complex of DNA and protein found in the nucleus of a cell.
Chromatin remodeller Proteins that use the energy from ATP to move nucleosomes, bringing about changes in chromatin compaction.
Chromosome
An organised structure of DNA and protein found in the nucleus of a cell. Diploid human cells have 46
chromosomes: 22 pairs of autosomes and 2 sex chromosomes.
Chromosome territory The subcompartment in the nucleus where a particular chromosome resides.
Cis Acting on the same molecule of DNA
Constitutitive
heterochromatin
Heterochromatin that is the same in all cell types, eg. centromere, telomere.
CpG island Clusters of CpG dinucleotides often found at promoters of genes.
CpG island shore CpG dinucleotides situated a short distance away from CpG islands.
Differentially Methylated
Domain (DMD)
A region of DNA that controls the expression of imprinted genes. Also known as an Imprint Control Region
(ICR) or Differentially Methylated Region (DMR).
Differentially Methylated
Region (DMR)
A region of DNA that controls the expression of imprinted genes. Also known as an Imprint Control Region (ICR) or
Differentially Methylated Domain (DMD).
Differentiation The process by which cells acquire specialised structures and functions during development.
Diploid Containing two sets of chromosomes (2n); one set is inherited from the mother, the other set from the father.
Distal Situated far away in the DNA.
DNA methylation Methylation of the 5' group of cytosines within CpG dinucleotides.
Dosage compensation The process by which somatic cells of males and females express the same levels of X-linked genes.
Embryonic stem cell
Cells derived from the inner cell mass of a blastocyst. Embryonic stem cells are pluripotent, i.e. they have the
potential to differentiate into all of the embryonic cell types.
Epiblast
The layer of an early embryo that will give rise to the embryo-proper (rather than the extra-embryonic
membranes).
Epigenetic reprogramming The erasure and remodeling of epigenetic marks, eg. in germ cells and during early development of an embryo.
Epigenetics The study of mitotically heritable changes in gene expression that occur without changes in DNA sequence.
Epimutation A heritable change in gene expression that is not accompanied by a change in DNA sequence.
Euchromatin An open form of chromatin that is highly accessible to proteins involved in DNA replication and transcription.
Expressivity The degree to which individuals carrying a particular genotype display the corresponding phenotype.
Facultative
heterochromatin
Heterochromatin that can differ by cell type.
Fertilisation
Joining of two haploid genomes to form a diploid zygote. In humans, this occurs when the male gamete (sperm)
fuses with the female gamete (egg).
Fluorescence in situ
hybridization (FISH)
A technique in which a fluorescent probe binds to its complementary sequence in the genome. Fluorescent
microscopy is then used to localise the probe on chromosomes.
Fluorophore A chemical compound that emits fluorescent light upon excitation.
Gastrulation
The process in development when an embryo transforms from a hollow ball of cells to a two-layered, cup-

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Gastrulation
The process in development when an embryo transforms from a hollow ball of cells to a two-layered, cup-
shaped embryo.
Gene A specific sequence of DNA that codes for a protein.
Genomic imprinting The process by which genes can show monoallelic expression based on the parent-of-origin of the allele.
Germ cell A haploid cell, e.g. egg or sperm.
Haploid Containing only one set of chromosomes (1n). Germ cells are haploid.
Haplotype A group of alleles that are located closely together on the same chromosome.
Heterochromatin
A tightly packaged form of chromatin that is poorly accessible to proteins involved in DNA replication and
transcription.
Heterozygous A diploid organism with two different alleles for a given gene.
Histone A positively charged protein that binds to DNA to form a nucleosome, the smallest unit of chromatin.
Histone modifications Post-translational modifications of the N-terminal tails of histones.
Histone variant Histones with varying stabilities or specialist domains that alter the function of the nucleosome.
Homologous chromosomes
A pair of chromosomes that bear the same genes. One chromosome is inherited from the father, the other from the
mother.
Homozygous A diploid organism with two copies of the same allele for a given gene.
Identical twins Twins that are genetically identical as they arise when one embryo splits into two during early development.
Imprint Control Region
(ICR)
A region of DNA that controls the expression of imprinted genes. Also known as a Differentially Methylated
Domain (DMD) or Differentially Methylated Region (DMR).
Imprinted gene A gene that shows monallelic expression based on the parent-of-origin of the allele.
Induced Pluripotent (iPS)
cell
An embryonic stem cell-like pluripotent cell produced from a somatic cell via somatic cell reprogramming.
Inner cell mass The mass of cells inside the blastocyst that will give rise to the embryo proper. Cells of the ICM are pluripotent, and
can be used to derive embryonic stem cells.
Insulator A boundary element that prevents the interaction between an enhancer and a promoter.
Interphase The period of the cell cycle when the cell is not undergoing division.
Karyotype The number and appearance of chromosomes in the nucleus of a eukaryotic cell.
lncRNA
Long non-coding RNA: long (>200 nt) RNAs that are not translated into proteins, and are largely constrained to the
nucleus.
Meiosis
The process of cell division that generates haploid cells from diploid cells. Meiosis occurs in two stages to
halve the number of chromosomes in the resulting germ cells.
Metaphase
A phase of mitosis when the replicated chromosomes are aligned in the centre of the nucleus prior to distribution
among the two daughter cells.
Metastable epiallele
An alelle that shows variable expression in genetically identical individuals due to epigenetic modifications
of the allele.
miRNA
Micro RNA: RNA that leads to post-transcriptional gene silencing through mRNA cleavage or repression of
translation.
Mitosis
The process of cell division. During mitosis the chromosomes are replicated before being equally distributed
among the two daughter cells, conserving chromosome number.
Monoallelic gene
expression
Expression of only one allele in a diploid cell.
Morula An early stage of embryo development consisting of a solid mass of cells with a mulberry appearance.
mRNA
Messenger RNA: RNA that codes for a protein. The information in mRNA is used to produce a polypeptide during
translation.
Nuclear lamina A structure on the inner nuclear membrane composed of lamin proteins.
Nuclear pore A hole in the nuclear membrane allowing transport between the nucleus and the cytoplasm.
Nucleolus The subcompartment of the nucleus where ribosomes are synthesised.
Nucleosome
The basic unit of chromatin, consisting of 146 bp of DNA wrapped around a histone octamer (2 x H2A, 2 x H2B, 2 x
H3, 2 x H4) linked by exterior histone H1.
Oncogene A gene that promotes cancer, e.g. through promoting survival and proliferation.
piRNA Piwi-interacting RNA: RNA involved in silencing transposable elements in the germ line and in stem cell populations.
Paramutation
An epigenetic phenomenon in which one allele at a locus induces a heritable change in the other allele at that
locus.
Penetrance The proportion of individuals carrying a particular genotype who display the corresponding phenotype.
Placenta
An organ that connects the developing fetus to the wall of the uterus, enabling uptake of nutrients,
elimination of wastes and exchange of gases.
Pluripotent cell A cell that has the potential to differentiate into several types of mature cells.
Position Effect
Variegation (PEV)
Variegation that results when heterochromatin spreads into adjacent genes, silencing their expression.
Post translational
modification
Modification of a protein after it has been synthesised by translation; modifications include but aren't limited
to acetylation, methylation, phosphorylation and ubiquitination.

3. 01/07/13 Wiki - Glossary | Epigenetic Control of Gene Expression
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Created Mon 15 Apr 2013 5:10 PM PDT (UTC -0700)
Last Modified Thu 20 Jun 2013 9:18 PM PDT (UTC -0700)
modification to acetylation, methylation, phosphorylation and ubiquitination.
Primordial germ cell Cells that will later give rise to the germ cells, oocytes and spermatozoa. These cells are pluripotent.
Promoter Regulatory region at the start of genes, where the transcription machinery binds.
Protamine Proteins that replace histones in the chromatin during the late stages of spermatogenesis.
Proximal Situated nearby in the DNA.
Pseudoautosomal region A region of a sex chromosome that is homologous between the X and the Y chromosome.
Recombination Exchange of genetic material between chromosomes.
Repetitive element
Nucleotide sequences found in multiple copies in the genome. The repeated sequence may be short and found
together (in tandem) or long and dispersed through the genome. Repetitive elements are usually non-coding.
Replication timing Temporal segregation of replication for euchromatin or heterochromatin.
RNA polymerase The enzyme that catalyses the synthesis of RNA during transcription.
rRNA Ribosomal RNA: RNA that forms the structure of ribosomes.
Sex chromosomes
The chromosomes responsible for sex determination. In humans, females have two X chromosomes while males
have an X chromosome and a Y chromosome.
Single Nucleotide
Polymorphism (SNP)
A common type of genetic variation consisting of differences at a single nucleotide position.
Skewed X inactivation A preference to inactivate one X chromosome over the other.
SnoRNA Small nucleolar RNAs: RNA molecules that guide chemical modifications of other RNAs.
Somatic cell Any cell in a multicellular organism apart from the germ cells.
Telomere Repetitive DNA at the ends of chromosomes that performs a protective function.
Totipotent cell A cell that has the potential to differentiate into all the cell types of an organism.
Trans Acting on a different molecule of DNA.
Transcription Synthesis of RNA from a DNA template.
Transcription factor A protein that binds to regulatory sequences in a gene and promotes transcription.
Transcription factory
A subcompartment of the nucleus where there is a concentration of transcription machinery and active transcription
occurs.
Transgene A gene transferred from one organism to another.
Transgenerational
epigenetic inheritance
The epigenotype of the parent influences the epigenotype observed in the offspring, and cannot be attributed to cis -
acting genetic alterations. The hypothesis is that this is due to a failure to clear some epigenetic marks during
gametogenesis and early embryogenesis.
Translation Synthesis of a polypeptide using the instructions in mRNA.
Translocation An aberration in DNA due to the attachment of a chromosome fragment to a non-homologous chromosome.
Transmission ratio
distortion
Deviation from the expected Mendelian proportions of each genotype.
Transposon An element in DNA that can move around the genome leading to genetic instability.
tRNA Transfer RNA: RNA that brings an amino acid to the appropriate codon in mRNA during translation.
Trophectoderm The cells forming the outer layer of the blastocyst; these cells give rise to the placenta.
Tumour suppressor gene A gene that acts to prevent cancer, e.g. through inhibiting survival and proliferation.
Uniparental disomy
Receiving two copies of a chromosome (or part of a chromosome) from one parent and no copies from the other
parent. UPD can be either maternal (receiving two maternal copies) or paternal (receiving two paternal copies).
Variegation
Mosaic expression of a gene among cells of the same type, for example the variegated coat colour observed
in mice and other animals.
X chromosome controlling
element (XCE)
A region near the XIC that influences X inactivation choice. Genetic differences in the XCE result in skewed X
inactivation.
X chromosome
inactivation The process by which one X chromosome is inactivated during early development of female embryos.
X inactivation Centre (XIC)
A region of the X chromosome (including the Xist gene) that regulates X inactivation. The XIC is necessary and
sufficient for X inactivation to occur.
Zygote The diploid cell formed by union of two haploid cells; in humans, the product when a sperm fertilises an egg.