Human Genetics: Concepts and Applications (Lewis), 9th EditionChapter 11:
Gene Expression and EpigeneticsChapter OutlineCHAPTER OVERVIEW
This chapter is concerned with the regulation of gene expression and its role in development. The complexity of gene expression varies from "hemoglobin switching" to the turning on and off of thousands of genes during the embryologic development of the human. An understanding of gene expression and development also requires a catalog of all the proteins produced by the genome. The field of proteomics is devoted to producing such a catalog. Mechanisms controlling gene expression include modification of chromosomal proteins (histones), production of transcriptional factors, and repression of translation by microRNAs. The genome can produce more proteins than it has genes by means of alternate splicing. Only 1.5% of the genome encodes proteins; the remainder includes introns, non-coding RNAs, HERVs, regulatory sequences, and repeated DNA.CHAPTER OUTLINE11.1 Gene Expression Through Time and Tissue- Epigenetic changes do not alter the DNA sequence but modify gene expression. They may be passed on to daughter cells.
- "Globin chain switching" accounts for the production of different hemoglobins at different times during development.
- Changes in gene expression are responsible for the development of different cell types, tissues, and organs.
- Specialized cells develop from stem cells.
- The proteome is the total number of proteins produced by the organism.
- The pattern of genes that are overexpressed or underexpressed may have medical implications.
11.2 Control of Gene Expression- Modification of histone chromosomal proteins affects the structure of the chromosome and its transcription.
- MicroRNAs are small non-coding RNAs that repress the translation of many mRNAs by binding their 3' ends.
- MicroRNAs may be used for medical therapy in the future.
- In a similar way, researchers are using small synthetic RNAs to interfere with the production of certain proteins. This technique is called RNA interference (RNAi).
11.3 Maximizing Genetic Information- Differential use of introns and exons through alternate splicing explains how one gene can produce more than one protein.
- Intron sequences of one gene may contain the coding sequences for another protein.
11.4 Most of the Human Genome Does Not Encode Protein- About 98.5% of the human genome does not code for protein.
- About 8% of the human genome, approximately 100,000 DNA sequences, are thought to be human endogenous retroviruses (HERVs).
- Much of the human genome produces non-coding RNAs (rRNA, tRNA, snRNA, snoRNA, etc.).
- Part of the human genome is composed of pseudogenes. These may or may not be transcribed, and are never translated into protein.
- A large part of the human genome is composed of repeat sequences such as transposons.
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