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Do you ever heard the word: Chromosome? Hehe, yes I think. Chromosome is a nukleat acid molecule that structured by DNA (Deoxiribose Nucleat Acid). The DNA’s are bonded to protein (protein non-histon for procariot) or histon protein (in eucariota), and have ability to make an own-replication (Corebima, 1994). At eucariotic cells, you can find chromosomes in nucleus and also found in certain organels, for example chloroplast for plant cell and mitochondria for animal cell. Chromosome structure in any mitochondrial organism always in double helix form which twine and doesn’t associate with histon or other proteins. In other word, the DNA in naked double helix form (Corebima, 1994). Differing from chromosome in mitochondria, chromosome in eucariot cell nucleus is nucleoprotein which consist of double helix DNA that have associate with histon protein, non-histon protein even RNA too (Gardner, 1991).
Some of insect cell have a giant chromosome, one of them are Drosophila melanogaster (fruit fly). The giant chromosome found in its salivary glands (Kimball, 1990). This chromosome called as giant chromosome because in fact the chromosome is in interphase and have longer form than metaphase chromosome. This condition make them can easily to see although in interphase, that a regular interphase chromosome can’t be see. Giant chromosome formed by endo-mitosis process, a replication process that make many chromosome but doesn’t breakaway one and other. Giant chromosome structure contain of dark ribbon and light ribbon. The light ribbon consist of eucromatin with distantly winding, but dark ribbon consist of heterocromatin with thickly winding, condensed and taking action in cell duplication process. Generally, a dark ribbon contain a many of DNA (Deoksiribose Nukleat Acid) (Kimbal, 1990).
The giant chromosome is a product form multi-duplication process of chromosome but without cell duplication. This homolog duplicates, a maternal and also paternal, located side by side, so make a form like a cable with many fiber. For example, in Drosophila melanogaster salivary gland, giant chromosome is formed by nine times replication cycle of chromosome.
Well, we will explain the research to find a giant chromosome step-by step:
Tools and materials:
• Light microscope
• Flat glass
• Object glass
• Cover glass
• Small knife
• NaCl liquid 0,9%
• Larva of Drosophila melanogaster
• Choose third instar of Drosophila melanogaster larva
• Put the larva in flat glass, add NaCl 0,9%
• Cut the larva, and take its head
• See under the light microscope and find its salivary gland (some think looks like small transparent kidney)
• Put the salivary gland that clean from lipid on object glass
• Add FAA until the colour of salivary gland not transparent anymore
• Absorb the FAA scrap with tissue
• Add acetocarmine and cover the specimen with cover glass
• Put under the light microscope
• See! Find the giant chromosome and take a picture of them
Polytene Chromosome, (Online), (www.ucsf.edu/sedat/polytene_chrom.html, access: march, 2007).
Polytene Chromosome (2), (Online), (http://en.wikipedia.org/wiki/Polytene_chromosome, access: march, 2007)
Polytene Chromosome, Endoreplication and Puffing, (Online), (http://www.sdbonline.org/fly/aimorph/puffing.htm, access: march, 2007)
Polytene Chromosomes from Salivary Glands, (Online), (http://www.woodrow.org/teachers/bi/1994/polytene_chromosomes.html, access: march, 2007)
Corebima, A.D. 1994. Genetika. Malang: UM Press
Gardner, E.J, dkk. 1991. Principles of Genetics. New York: John Wiley and Sons, Inc.
Kimball, W, John. 1990. Biologi Jilid I. Jakarta: Erlangga
Manning, Gerard. 2006. A Quick and Simple Introduction to Drosophila melanogaster, (Online), (www.ceolas.org/fly/intro.html, access: march, 2007)
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