46 all somatic cells have 46 except for germinal cells(sperm and eggs) who have 23 chromosomes.
Every cell in the human body, apart from enucleated red blood cells and the haploid gametes, has 23 pairs of chromosomes (for a total of 46). One copy of each pair is inherited from the mother and the other copy is inherited from the father. The first 22 pairs of chromosomes (referred to as autosomes) are numbered from 1 to 22, and are arranged from largest to smallest in a karyotype (see figure). The 23rd pair of chromosomes are the sex chromosomes. Normal females have two X chromosomes, while normal males have one X chromosome and one Y chromosome.
During meiosis, when germ cells divide to create sperm and egg (gametes), each half should have the same number of chromosomes. But sometimes, the whole pair of chromosomes will end up in one gamete, and the other gamete will not get that chromosome at all.
Most embryos cannot survive with a missing or extra autosome (numbered chromosome) and are spontaneously aborted. The most frequent aneuploidy in humans is trisomy 16, although fetuses affected with the full version of this chromosome abnormality do not survive to term (it is possible for surviving individuals to have the mosaic form, where trisomy 16 exists in some cells but not all). The most common aneuploidy that infants can survive with is trisomy 21, which is found in Down syndrome, affecting 1 in 800 births. Trisomy 18 (Edwards syndrome) affects 1 in 6,000 births, and trisomy 13 (Patau syndrome) affects 1 in 10,000 births. 10% of infants with trisomy 18 or 13 reach 1 year of age.
Changes in chromosome number may not necessarily be present in all cells in an individual. When aneuploidy is detected in a fraction of cells in an individual, it is called chromosomal mosaicism. In general, individuals who are mosaic for a chromosomal aneuploidy tend to have a less severe form of the syndrome compared to those with full trisomy. For many of the autosomal trisomies, only mosaic cases survive to term. However, mitotic aneuploidy may be more common than previously recognized in somatic tissues, and aneuploidy is a characteristic of many types of tumorigenesis (see below).
by paarsurrey 3 years ago
Garza-Valdes, together with Victor and Nancy Tryon, has carried out a PCR DNA test on blood samples taken from the Shroud (, pp. 115-119). He conducted a standard sex determination test. He looked for, and found, fragments of the amelogenin-X gene, which is found only on the X-chromosome, and...
by TMMason 9 years ago
I enjoy this video so very much.http://www.youtube.com/watch?v=MX7Htg2HxkA&NR=1Abaa.. ah... ah... aba... what?I love that video... not to mention the fact that he never answered the question. Yes, I have read his letter to his fans as to his answer. And it is almost as funny as the video.The...
by qwark 8 years ago
The human cell can under optimum conditions (no stress), live to about 160 yrs.Will that life span, eventually, be extended?Will genetic engineering create the potential for human immortality?Your reasons negative or positive.Qwark
by ngureco 7 years ago
Why Is Color Blindness More Noticeable In Men Than In Women?
by jite 9 years ago
what is trisomy 21 in pregnancy
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