Human genome
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Human genome is the genome of Homo sapiens. It is made up of 23 chromosome pairs with a total of 3×109 base pairs. There are about 30,000 genes in human DNA. This was only twice as many as much simpler organisms, such as the roundworm and the fruit fly. However, human genes can make proteins by alternative splicing, allowing humans to make more proteins than simpler organisms; because of this, the human proteome is about ten times larger than those of the aforementioned organisms. This was much lower than the projected 100,000 genes many scientists predicted, allowing the project to be completed way ahead of schedule. The human genome was mapped by the human genome project. This mapping was finished to 99% on April 14, 2003.
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Features
Human genetic material is made up of two distinct components: the nuclear genome and the mitochondrial genome.
The Nuclear Genome
The nuclear genome has 24 kinds of chromosomes: numbers 1 through 22 plus the X chromosome and its smaller partner, the Y chromosome. Both men and women inherit 22 chromosomes from each parent, plus an X chromosome which is always inherited from the mother. Women inherit another copy of the X chromosome, and men a copy of the Y chromosome, from the father.
The Mitochondrial Genome
Both men and women inherit their mitochondrial DNA (mtDNA) from their mother. This allows scientists to trace the origins of the human race and the evolution of humans from other hominids.
Internal Features
About 97% of the human genome has been designated as "junk" DNA. For example, the Alu sequences are repeated some million or so times, and this one family alone accounts for about 5% of human DNA. Single nucleotide polymorphisms make up 90% of all human genetic variations, and occur every 100 to 300 bases along the human genome. At this point in time, it is unknown whether this junk DNA has any purpose.
Gene density throughout the genome is uneven. Some chromosomes have relatively few genes when compared to others. The density of genes on the different chromosomes varies from 23 genes per million base pairs on chromosome 19 (1,400 genes) to only 5 genes per million base pairs on chromosome 13.
From the genome, scientists learned that humans share many genes with vertebrates, but not with invertebrates. Vertebrates contain many more genes programmed to initiate apoptosis than the simpler invertebrates, along with molecules that participate in blood clotting, antibody production, and cell-signaling (cytokines).
The Genetic Landscapes
The modern human genome shares more than 97% of its DNA with the rest of the genomes in the Hominid family.
Implications
The completion of the genome will be of great aid to doctors treating patients with genetic disorders and to scientists studying genetics and evolutionary biology. However, the genome will also aid controversial practices such as cloning and genetic engineering.