Major features of human genome

TABLE 1! l Major Features ofthe Human Genome I The human genome Contalns 3.1 larlllon nucleondes, out protern-cod‘mg sequences make up only about 2 percent 0F the genome. I The genome sequence ls -99.9 percent simllar .n indlvldut als orall nanonal s, 5st and copy numberyanatlons (CNVs) account For genome dwersny From person to person, I The genome l5 dynamrc. Ar least 50 percent orthe genome ls derwed from transposahle elements, such as um and AM sequences, and other repe e DNA sequences I The human genome conta‘lns approxlmately 20,000 proteln- codlng genes, rar rewerthan the ongrnally predrcted number «300007100000 genes. I The average srze ofa human gene is ~25 kb, lncludlng genet regulatory regrons, introns, and exons. On average, mRNAs produced by human genes are ~3000 or long. I Many human genes produce more than one ploteln through alternatlye spllclng, thus enalohng human cells to produce a much larger number orproteins (perhaps as many as 200,000) From only ~zo,000 genes, I More than 50 percent orhuman genes show a hlgh degree orseduence slmllarlty to genes m other organlsms; however, more than 40 percent orthe genes Identlfied have no known molecular runcnon I Genes are not unlformly dlsrrlbuted on the 24 human thro— mosomes. Genench clusters are separated by genetpoov “deserts" that account for 20 percent orthe genome. These deserts correlate with a band; seen in stalned chromot somes,Chromusome19 has the hlghest gene denslty, and chromosome l3 and the v chromosome have the lowest gene densltles. I chromosome 1 contains the largest number orgenes, and the vthromosome tonralns the smallest number. I Human genes are largerand contain more and larger lnrrons than genes m the genomes orlnyertehrates, such as pro mph/Ia The largest known human gene encodes dystrophln, a muscle protein. Thrs gene, assocrated m mutant rorm wrth muscular dystrophy, Is 2 5 Mb m length (chapter l4), larger than many hattenal chromosomes. Most orthls gene ls composed orlntrons. I The number oFirltrons m human genes ranges From 0 (.n hrstone genes) to 234 (In the gene Fortltm, whlch encodes a muscle protem),