11.4 Flashcards
chromosome territory
a small region of the nucleus that is the domain of a single chromosome. It is not bounded by any sort of membrane, nor is it demarcated in any distinctive manner.
each chromosome territory differs from nucleus to nucleus, but once confined to a territory, a chromosome does not stray from it until the initiation of M phase of the cell cycle
chromosomes are dynamically active in their territories during interphase and can be seen to move, twist, and turn during transcription and DNA replication.
chromosomes seem to take positions that allow for each chromosome characteristic patterns of gene expression and other activities during interphase
interchromosomal domain
the space between chromosome territories that contain no chromatin
They are channels for the movement of proteins, enzymes, and RNA molecules withnin the nucleus and among chromosome territories.
how are chromosome territories distributed?
the largest and most gene rich chromosomes are towards the center of the nucleus, while the territories of smaller chromosomes containing fewer genes are located toward the outer edges of the nucleus
facultative heterochromatin
Heterochromatic chromosome regions whose level of compaction can vary. Often contains repetitive DNA, but may also contain some expressed genes
heterochromatin is compacted for the most part though
constitutive heterochromatin
chromosome regions containing chromatin that is always densely compacted. Usually containing highly repetitive DNA sequences.
euchromatin
chromosome regions containing chromatin that is not densely compacted. most expressed genes are located within euchromatic regions of chromosomes. Also known as euchromatic region.
position effect variegation (PEV)
expression of the gene is dependent on its position with respect to centromeric heterochromatin
its an epigenetic phenomenon in which gene expression is determined by chromatin structure (which is determined by location in the chromosome)
transmissible during mitotic cell division
see fruit fly eye color example on page 374
E(var) mutations
E(var) is short for enhancers of position effect variegation
they increase or enhance the appearance of the mutant white-eye phenotype by encouraging the spread of heterochromatin beyond its normal boundaries. The effect of the mutation is to produce a greater number of eye cells lacking pigment
this is pertaining to the Drosophilia fruit fly
Su(var) mutations
Su(var) is short for suppressors of position effect variegation
restrict the spread of heterochromatin or interfere with its formation
Su(var) mutations increase the extent of normally pigmented regions of the eye by suppressing the emergence of white patches.
