DNA in plants and other organisms is packaged into structures called chromosomes. Chromosomes are found in the nucleus of the plant cell. The structure of the chromatin that makes up chromosomes is important in regulation of gene expression.
The number of chromosomes and the amount of DNA in a plant cell varies depending on the species. According to the Harvard University Gazette, the onion, for example, has a genome 12 times as large as the human genome. Some plants have two copies of each chromosome just like humans, while other plants have three, four, five or even six copies of all their chromosomes.
Like animal chromosomes and unlike bacterial chromosomes, plant chromosomes are linear. Plant chromosomes are composed of chromatin, a combination of proteins and DNA. A strand of DNA winds around a core of histone proteins to form a nucleosome, a little like a bead on a string. Nucleosomes are in turn arranged into larger arrays or fibers that form the chromosome.
Changes in chromatin structure can help determine which genes are expressed in a given cell; if the chromatin in a given region is tightly packed, the proteins that transcribe DNA may not be able to access genes in that region, so the genes may be suppressed or "silenced."
- Harvard University Gazette: Why Onions Have More DNA than You Do
- "Genetics: A Conceptual Approach"; Benjamin A. Pierce; 2006
- Photo Credit Jupiterimages/Photos.com/Getty Images
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