遗传学精品教学（南京大学）Chapter 3 Human Genomics I.pptVIP

* Key Result (2) The actual number of genes is smaller than previously estimated. The human genome has an unexpectedly small number of genes (30,000, previous estimates between 50,000 and 100,000 genes), half of which function is unknown The human genome is nearly the same in all people (99.9%) Surprisingly, humans have a small coding genome. only a third larger than a nematode worm! * Key Result (3) The protein products of many genes remain unknown. It has been found that many of the known genes can be translated in different ways to produce alternative protein variants from the same gene. Thus, although we have only twice as many genes as fruitflies, we may have five times as many different proteins. * Key Result (4) A very high percentage of our genes are not unique to humans but are closely similar to comparable genes from other species. In fact, only 1% of human genes have no sequence similarity to any other organisms Our genes are similar to 46% of genes in yeast More than 200 human genes and their protein products have been found to have significant similarity to those in bacteria Among mammals the differences are even fewer. Humans have only 300 genes that have no counterpart in the mouse genome. What we learned from the sequence of human genome is how very like other organisms we are It seems transfer of gene from one species to another, not only by artificial means of genetic engineering, but also occurs in nature. * Guess： In a mouse these unique genes are linked to and --. smell and reproduction More than 90 percent of genes associated with disease are identical in humans and mice ? the tremendous value of the mouse in laboratory experiments. * Key Result (5) Within each single gene, there is an average of 15 sites at which different individuals carry a different nucleotide. ? These variations, called single nucleotide polymorphisms (SNPs), are greatly expanding how many alleles we think are possible for different genes ? Most of th