THE GENETIC FUNCTIONING OF HETEROCHROMATIN. Final Report
The general properties of chromosome regions that are described as being heterochromatic are discussed. Since these chromosome regions contain relatively few genes, as defined by the usual operational techniques, their genetic function is unveiled only in rather special situations such as position-effect variegation. Although these situations may be special, the heterochromatic portions of chromosomes are appreciable in size. In most species of Drosophila, from a fourth to a half of the proximal portion of each chromosome arm is heterochromatic in the usual somatic cell. The effect of heterochromatin on gene action can easily be detected by using chromosome rearrangement which relocated the wild-type allele of a gene that normally resides in auchromatin to a region of heterochromatin. Under these circumstances, the usual dominant behavior of the wild-type allele does not prevail with the result that in some somatic cells the recessive characteristics are shown, thus producing variegated tissue. In addition to this direct effect on gene action, the addition or subtraction of heterochromatin to the genome affects the action of the gene when it is involved in such a chromosome rearrangement. Therefore, the phenomenon of position-effect variegation offers a tool for determining qualitative and quantitative effects of hetercchromatic regions on gene action. The effects of hetercchromatin are not limited to gene action since it has been shown that these regions located in different chromosomes still share some homology and thus they are important in chromosome pairing, crossing over, and disjunction. In particular, heterochromatic regions may play an important role in the interchromosomal effects on crossing over and disjunction; i.e., the heterochromatic constitution on one pair of chromosomes may affect the amount of recombination in another non-homologous pair. A brief summary is presented of the results of studies on the functioning of heterochromatin. (C.H.)
- Research Organization:
- Chicago. Univ.
- NSA Number:
- NSA-15-023196
- OSTI ID:
- 4037876
- Report Number(s):
- TID-12830
- Country of Publication:
- United States
- Language:
- English
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