In the Evidence section, Shenk shows support for his statement "estimates of the actual number of genes vary" on page 19. He tells of how "the exact number of genes encoded by the genome is unknown". Estimates have included 19,599 protein coding genes with 2,188 more DNA segments that could code for protein and these numbers were thought to be low for our species. He also defends another statement said on page 19 which was " genes -- all twenty-two thousand of them -- are more like volume knobs and switches." He explains that this statement was merely a metaphor to capture how genes work in a general sense (182-183).
How is the number of genes low for our species? Why is the number of genes that code for proteins so low in our species? (Explain how the number is so low (i.e. what happens within genome to make it so low)). Does the gene number of any other species come close to ours? Explain Shenk's metaphor of how genes are like volume knobs and switches. (Regan Frieling, regan1995@yahoo.com).
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ReplyDeleteAs a basis of comparison, a fruit fly has approximately 14,000 genes. However, because of the process of RNA editing and alternative splicing in humans as discussed in Chapter 17 of Campbell, we can code for many more proteins even though we only have approximately 19,599 protein coding genes. This number was considered low when the human genome project began (Partially because of the belief that if such 'simple' animals as fruit flies had 14,000 genes, humans, being much more complex, should have considerably more.), because scientists hadn't yet fully grasped the understanding of alternative splicing and the idea that a single gene can code for multiple proteins (http://genome.wellcome.ac.uk/doc_WTD020807.html).
ReplyDeleteAs for Shenk's metaphor of genes in relation to volume knobs and switchboards. Humans pressing and turning and flipping the switches in comparable to hormones activating genes. Different environments will cause the introduction of different hormones that will activate only certain genes. Sometimes, the genes will be translated and transcribes many times, so that more of the protein is synthesized, and the volume is turned 'louder'. Other times, when you mess with the pitch, bass, or add other sounds, a different sound is created. This is similar to the multiple proteins that need to be synthesized in order to create a single trait.
Cassidy Levy (clevy3)