Genome size and determination of DNA content of the X chromosomes, autosomes, and germ line-limited chromosomes of Sciara coprophila
✍ Scribed by Ellen M. Rasch
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 356 KB
- Volume
- 267
- Category
- Article
- ISSN
- 0362-2525
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✦ Synopsis
Abstract
The unique chromosome biology of the fungus fly Sciara coprophila has fascinated investigators for over 80 years. Male meiosis exhibits a monopolar spindle, nonrandom segregation of imprinted chromosomes and nondisjunction of the X chromosome. The unusual mechanism of sex determination requires selective elimination of X chromosomes in embryogenesis. Supernumerary (L) chromosomes are also eliminated from the soma during early cleavage divisions. Distinctive DNA puffs on the larval salivary gland chromosomes are sites of DNA amplification. As a foundation for future genome studies to explore these many unusual phenomena, we have used DNA‐Feulgen cytophotometry to determine genome size from hemocyte nuclei of male (X0) and female (XX) larvae and adults. The DNA content of the X chromosome is ∼0.05 pg DNA and the autosomal complement is ∼0.45 pg DNA. Measurements of DNA levels for individual sperm from adults showed that the DNA contribution of the germ line‐limited (L) chromosomes constitutes as much as 35% of the DNA of the male gamete. A parallel study using Sciara ocellaris, a related species lacking L chromosomes, confirmed the presence of two X chromosomes in the sperm of this species. J. Morphol., 2006. © 2006 Wiley‐Liss, Inc.