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10-31 - BIO 5099 Molecular Biology for Computer...

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BIO 5099: Molecular Biology for Computer Scientists (et al) Lecture 19: Eukaryotic genes & Multicellular Organisms http://compbio.uchsc.edu/hunter/bio5099 [email protected] Gene Families In metazoans, 50-75% of genes are found in groups of similar but slightly different sequences called gene families . Example: Human °-globin, which transports oxygen in the blood, has 7 variants, 2 of which are expressed fetally. These arise from gene duplication events . Similar to homologous recombination, but during sexual reproduction, makes an extra copy of the gene Tandem repeats have identical members. Example: histones, rRNAs, tRNAs Pseudogenes are untranscribed duplicates. Repeated DNA elements Certain genes that are transcribed at high levels must have many tandem repeats Number of repeats is gene copy number . All Eukaryotes have copy number > 100 for the 5S rRNA. Embryonic human cells have 5-10 million ribosomes, and reproduce every 24 hours. That's a lot of rRNA synthesis! Frogs have a 5S rRNA copy number of >20,000! Human DNA is also full of “junk” repeats of many varieties (ALUs, LINES, SINES, etc.)
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Gene Duplication and Evolution Gene duplication events are very important in the evolution of new functions for old genes. Genes that are similar to other genes in the same genome are called paralogs . Duplications allow mutation without loss of old function. Deactivated pseudogenes are even freer to mutate. Reactivation can restart transcription of changed gene. Multicellular Organisms We've covered the basic activities of the Eukaryotic cell. Now we will look at additional activities of cells in multicellular organisms Somatic vs. germ line cells & sexual reproduction Specialized cell types and tissues Development Cell to cell signaling and control Then we will look at theories of the evolutionary origins of multicellular organisms The fundamental deal of multicellularity Multicellular organisms are distinguished from colonies of unicellular organisms by the specialization of their constituent cells.
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