What triggers heterochromatin formation?

At centromeres, heterochromatin formation is directed by RNA interference (RNAi) a naturally occurring process in the nucleus of eukaryotic cells that silences gene expression (Figure 2).

Does Drosophila have heterochromatin?

Centromeric heterochromatin comprises ∼30% of the Drosophila melanogaster genome, forming a transcriptionally repressive environment that silences euchromatic genes juxtaposed nearby. Surprisingly, there are genes naturally resident in heterochromatin, which appear to require this environment for optimal activity.

Is heterochromatin active or inactive?

Heterochromatin is “inactive” chromatin, which prevent DNA metabolism such as transcription and recombination (Fig. 1). The basis of the inactiveness has been thought the tight packaging of the nucleosome array, which prevents access of enzymes promoting the DNA metabolism.

How does heterochromatin affect gene expression?

Heterochromatin is a constituent of eukaryotic genomes with functions spanning from gene expression silencing to constraining DNA replication and repair. Inside the nucleus, heterochromatin segregates spatially from euchromatin and is localized preferentially toward the nuclear periphery and surrounding the nucleolus.

What do we call an element that directs initiation from a number of weak transcription start sites?

A focused promoter specifies transcription initiation at a single specific nucleotide, whereas a dispersed promoter directs the initiation of transcription from a number of weak transcription start sites spread over a fairly wide region (50 to 100 nucleotides).

Does methylation cause heterochromatin?

This has established DNA methylation as an archetypal example of an epigenetic modification. In general, DNA methylation is thought to contribute to the formation of heterochromatic regions in the genome and transcriptional silencing.

Which description is the best definition of a single nucleotide polymorphism or SNP?

Which description is the best definition of a single nucleotide polymorphism, or SNP? any variation in a single DNA base between two individuals.

Where is heterochromatin found?

centromeres
Heterochromatin is a cytologically dense material that is typically found at centromeres and telomeres. It mostly consists of repetitive DNA sequences and non-coding RNA transcripts and is relatively gene poor.

Which of the following features is true for heterochromatin?

A) Heterochromatin of eukaryotic nucleus stains densely with simpler dyes than euchromatin. Heterochromatin has tightly packed DNA. Heterochromatin is observed both on the outer edge of the nucleus or buried withinside the indoors of a chromosomal domain. Hence, it is highly condensed in interphase.

Which of the following is a characteristic of heterochromatin?

A defining functional characteristic of heterochromatin is its capacity to exert a suppressive (position) effect. Expression of a MAR-binding protein, MATH20, in Drosophila relieved position effect exerted by pericentromeric repetitive DNA (49), previously shown to bind to the nuclear matrix (40).

What happens during the initiation step of DNA transcription?

Initiation is the beginning of transcription. It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. This signals the DNA to unwind so the enzyme can ”read” the bases in one of the DNA strands. The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases.