Human genetics
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A karyotype of a human male, showing 46 chromosomes including XY sex chromosomes. |
Humans (
Homo sapiens) are a
eukaryotic species. A human has 46
chromosomes (44
autosomes and 2
sex chromosomes, with an
XY sex determination system). At present estimate, humans have approximately 20,000-25,000
genes . Humans share 98.5% of their DNA with their closest living evolutionary relative, the
bonobos.
Humans have 46 chromosomes, arranged in pairs (i.e. they are
diploid). 44 (22 pairs) of these are
autosomes, and 2 are
sex chromosomes. Humans have an
XY sex determination system, so that
females have the sex chromosomes XX and the
males XY. The Y chromosome is shorter than the X chromosome, so that males are
hemizygous over this region. X-linked recessive genes are thus expressed more often in males.
Estimates of the number of genes humans have has been possible since
DNA sequencing was first introduced. Estimates however have varied wildly, though the present best guess is 20,000-25,000, estimates of up to 40,000 have been in the past.
In addition to
nuclear DNA, humans have
mitochondrial DNAHumans have several
genetic diseases, often caused by
recessive genes.
*
Genetic genealogy*
Genealogical DNA test*
Human Genome Project*
How many Genes do humans have?
