Heterochromatin and euchromatin

Heterochromatin

A tightly packed form of DNA that is transcriptionally inactive.

Euchromatin

A loosely packed form of DNA that is transcriptionally active.

Interphase chromatin.

The state of chromatin during interphase where DNA is dispersed for replication and transcription.

Mitotic chromosome

The highly condensed state of DNA during mitosis that facilitates proper segregation into daughter cells.

X inactivation

The process by which one of the X chromosomes in females is transcriptionally silenced.

Lyon Hypothesis

The theory stating that X chromosome inactivation occurs randomly in female mammals.

Barr body

The inactivated X chromosome in females, found as a condensed heterochromatic structure.

Constitutive heterochromatin

Regions of heterochromatin that remain compact throughout the cell cycle.

Facultative heterochromatin

Regions of heterochromatin that can become transcriptionally active depending on the cell type or conditions.

Histone code

The hypothesis that specific patterns of histone modifications dictate gene expression and chromatin structure.

Transcriptionally repressive

A characteristic of heterochromatin that inhibits gene expression.

Transcriptionally active

A characteristic of euchromatin that permits gene expression.

Methylation

The addition of a methyl group to DNA or histones, often associated with gene silencing.

Acetylation

The addition of an acetyl group to histones, often associated with gene activation.

Phosphorylation

The addition of a phosphate group to proteins, including histones, which can influence chromatin structure.

Position effect

A phenomenon where the position of a gene affects its expression, particularly when near heterochromatin.

Barrier sequences

Specialized DNA sequences that block the spread of heterochromatin along chromosomes.

Gene expression

The process by which information from a gene is used to synthesize a functional gene product.

Mosaicism in females

The presence of two different genetic cell lines in female mammals due to X inactivation of one X chromosome.

H3K9 methylation

Methylation of lysine 9 on histone H3, commonly associated with transcriptional repression.

Histone acetyltransferase (HAT)

An enzyme that adds acetyl groups to histones, promoting transcriptional activation.

Histone deacetylase (HDAC)

An enzyme that removes acetyl groups from histones, generally leading to transcriptional repression.

Chromatin compaction

The process by which chromatin structure becomes more condensed, affecting gene accessibility.

DNA hypermethylation

The addition of excessive methyl groups to DNA, typically leading to gene silencing.

DNA hypomethylation

Reduced levels of methylation on DNA, often associated with gene activation.

Gene silencing

The process through which a gene's expression is inhibited.

X-linked genes

Genes located on the X chromosome, which demonstrate unique inheritance patterns.

Calico cats

Cats with a patchy coat coloration caused by X-linked pigmentation genes, demonstrating X inactivation.

Telomeres

The ends of chromosomes that protect genetic data and are often rich in constitutive heterochromatin.

Transcription enzymes

Proteins that facilitate the process of transcription by synthesizing RNA from DNA.

Compacted chromatin

Chromatin structure that is tightly packed, limiting access for transcription and replication.

Dispersed chromatin

Chromatin structure that is loosely packed, allowing access for transcription and replication.

Recombination

The process through which genetic material is exchanged during meiosis or other forms of cell division.

Cell differentiation

The process by which cells become specialized in structure and function.

Genome

The complete set of genes or genetic material present in a cell or organism.

Gene activity

The level at which a gene is being expressed or transcribed into RNA.

Chemical modifications of histones

Post-translational changes to histones that can influence chromatin structure and gene expression.

Nucleosome

The basic unit of DNA packaging, consisting of a segment of DNA wound around histone proteins.

Gene clusters

Groups of related genes that are often transcribed together.

Somatic cells

Any cells forming the body of an organism, excluding germ cells.

Germ cells

Reproductive cells that give rise to gametes (sperm and eggs).

Transcription factors

Proteins that regulate the transcription of genes by binding to specific DNA sequences.

Alleles

Different versions of a gene that may produce different traits.

Telomere shortening

The gradual decrease in the length of telomeres associated with cellular aging.

Inactivation of genes

The process through which specific genes are rendered non-functional, impacting their expression.

Gene dosage

The number of copies of a gene present in a cell, affecting the amount of gene product produced.

Embryonic development

The process of development of an organism from fertilization to birth.

Transcriptional silencing

A mechanism that prevents the transcription of specific genes.

Chromatin remodeling

The dynamic modification of chromatin architecture to allow access to the DNA.

Histone tail modifications

Chemical changes to the N-terminal tails of histones that can affect chromatin structure.

Eukaryotic cells

Cells with a nucleus and organelles, including all plants and animals.

Position effect variegation

A phenomenon in which the expression of a gene is influenced by its chromosomal position.

Plasmid

A small, circular piece of DNA commonly used in genetic engineering.

DNA accessibility

The ability of transcription machinery to access DNA for gene expression.

Chromosomal regions

Segments of chromosomes that can show different biological functions and characteristics.

Barriers to transcription

Elements that prevent transcription machinery from accessing certain DNA sequences.

Genetic engineering

The direct manipulation of an organism's genome using biotechnology.

Histone variant

A variant form of a histone that can influence chromatin structure and function.

RNA polymerase

The enzyme that synthesizes RNA from a DNA template.

RNA splicing

The process of removing introns from the pre-mRNA and connecting exons.

Gene transcription

The process by which the information from a gene is transcribed into messenger RNA (mRNA).

Nucleosomal repeat

The repetitive structural unit of chromatin, containing DNA wrapped around a histone octamer.

Histone octamer

The core of eight histone proteins that DNA winds around to form a nucleosome.

Thermal stability

The ability of a molecule to remain stable at high temperatures, relevant to nucleosome function.

Metabolic regulation

Processes that monitor and control metabolic activities within an organism, influenced by gene expression.

Gene product

The end product of gene expression, typically a protein or RNA molecule.

Post-translational modification

Chemical modifications made to a protein after its synthesis, affecting its function.

Chromatin accessibility

The degree to which chromatin structure allows transcription machinery to bind and initiate transcription.

Transcriptional regulators

Proteins that bind to specific DNA sequences to influence the level of transcription of nearby genes.

Epigenetic modification

Heritable changes in gene expression that do not involve changes to the underlying DNA sequence.

Histone methylation

Modification of histone proteins by adding methyl groups, often associated with repression of transcription.

Cellular environment

The internal and external conditions surrounding a cell which can influence its function.