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The strandedness of meiotic chromosomes from Oncopeltus
Abstract:
Meiotic chromosomes were isolated from male Oncopeltus fasciatus by dissecting the testes under insect Ringer's solution and spreading the living cells on the Langmuir trough. After being dried by the critical point method, preparations were examined under the electron microscope. Chromosomes at all stages of prophase prove to be multistranded. A significant increase in the number of parallel 250 A fibers in the chromosomes occurs between zygotene and diakinesis. Parallel folding, rather than true multistrandedness, is interpreted as the mechanism responsible for this observed increase in multistrandedness. It has not been possible to determine whether the multistrandedness observed at leptotene represents true multistrandedness or is the result of parallel folding. Apparent multistrandedness is lost at metaphase when the 250 A fibers of the chromosomes become coiled more tightly. In preparations isolated by these methods, no structures other than the 250 A chromosome fibers are visible in the chromomeres, which appear as regionally coiled or folded areas of the fibers along the arm of the chromosome.
Insights
Meiotic chromosomes in Oncopeltus fasciatus appear multistranded due to fiber folding, not true strand multiplicity. This apparent multistrandedness changes during cell division, with fibers coiling tightly by metaphase.
Area of Science:
- Cell Biology
- Genetics
- Microscopy
Background:
- Meiotic chromosome structure is crucial for understanding genetic inheritance.
- Previous studies have suggested multistrandedness in chromosomes, but the underlying mechanisms remain debated.
Purpose of the Study:
- To investigate the structural organization of meiotic chromosomes in Oncopeltus fasciatus.
- To determine the nature of chromosome multistrandedness during meiosis.
Main Methods:
- Isolation of meiotic chromosomes from male Oncopeltus fasciatus testes.
- Preparation of living cells using Langmuir trough and critical point drying.
- Examination of chromosome structure using electron microscopy.
Main Results:
- Chromosomes exhibit apparent multistrandedness throughout prophase.
- A significant increase in parallel 250 Å fibers is observed from zygotene to diakinesis.
- Parallel folding of fibers, not true multistrandedness, is proposed as the cause.
- Apparent multistrandedness diminishes at metaphase due to tighter fiber coiling.
- Chromomeres are identified as regionally coiled or folded areas of 250 Å fibers.
Conclusions:
- The observed multistrandedness of meiotic chromosomes in Oncopeltus fasciatus is primarily attributed to parallel folding of 250 Å fibers.
- This folding mechanism explains the increase in apparent fiber number during prophase.
- Further research is needed to clarify the nature of multistrandedness at leptotene.