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The Human Genome—Structure and Organization 

The Human Genome—Structure and Organization
The Human Genome—Structure and Organization

Andrew P. Read

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date: 30 October 2020

Humans have two genomes, nuclear and mitochondrial. Normal diploid cells contain two copies of the nuclear genome and a much larger but variable number of copies of the mitochondrial genome. The phrase “the human genome” normally refers to the nuclear genome but should also include the mitochondrial genome. The successful completion of the Human Genome Project ushered in a new era in human genetics. The finished sequence is complemented by a rapidly increasing number of genome sequences from other species. The greater complexity of mammals compared with these organisms has been accompanied neither by a great increase in the number of genes nor by a significant increase in the number of different proteins produced per gene by alternative splicing, but by a vast increase in the amount of noncoding DNA with no known function. This hints at the existence of much more sophisticated systems for regulating gene expression, probably mediated by combinatorial binding of numerous proteins and small RNA molecules to some of the noncoding DNA, controlled by the local structure and organization of the chromatin. A major interest is in how the genome varies between people. Now that thousands of individual human genomes have been fully sequenced we have a much better picture of the range of normal variation and the evolutionary processes that produced that variation. Structural variants are numerous and often encompass genes. The average healthy person carries loss-of-function variants in around 100 genes, showing that not all our genes are essential. As clinical genetics services move more and more to sequencing as the default procedure, a major preoccupation is distinguishing pathogenic from normal variants.

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