Tag Archives: genetics

Klinefelter’s Syndrome


Klinefelter’s syndrome, also 47,XXY or XXY syndrome, is a genetic disorder in which there is at least one extra X chromosome to a normal human male karyotype, for a total of 47 chromosomes rather than the 46 found in genetically normal humans.  While females have an XX chromosomal makeup, and males an XY, individuals with Klinefelter syndrome have at least two X chromosomes and at least one Y chromosome.  Because of the extra chromosome, individuals with the condition are usually referred to as “XXY males”, or “47,XXY males”.
This chromosome constitution (karyotype) exists in roughly between 1:500 to 1:1000 live male births but many of these people may not show symptoms. If the physical traits associated with the syndrome become apparent, they normally appear after the onset of puberty. (Adapted from Wikipedia)

Klinefelter’s syndrome karyotype, Image from Wellcome Images (link)

Klinefelter’s syndrome karyotype 47,XXY
Klinefelter’s syndrome 47,XXY. This male has an extra X chromosome. Symptoms include deficiency of male hormones and underdeveloped secondary male characteristics, breast enlargement, small testes, infertility due to lack of sperm, and various psychopathological disorders.

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Picture n 51- DNA at X-Ray

X-ray diffraction diagram numbered 51 of the B form of DNA.  The dark cross let Watson and Crick know that the molecule was a double helix.  DNA (DeoxyriboNucleic Acid), the molecule that carries the genetic information, exists in two forms, A and B.  When in the B form, DNA is shielded in a sheath of water and thus, it is relatively free from the influence of neighboring molecules, the X-ray pattern being then, highly informative. (Image by Rosalind Franklin and Raymond Gosling, 1951. Caption adapted from Raquel Goncalves Maia, CFCUL)

Source: Watson, JD & Crick, FHC, Molecular Structure of Deoxypentose Nucleic Acids, Nature, Vol 171, pp 738-739, 25 April 1953

Link to different version of photo (here)

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FISH Chromosomes

FISH (fluorescence in situ hybridization) is a cytogenetic technique developed by biomedical researchers in the early 1980s that is used to detect and localize the presence or absence of specific DNA sequences on chromosomes.  FISH uses fluorescent probes that bind to only those parts of the chromosome with which they show a high degree of sequence complementarity.  Fluorescence microscopy can be used to find out where the fluorescent probe bound to the chromosomes.  FISH is often used for finding specific features in DNA for use in genetic counselling, medicine, and species identification. FISH can also be used to detect and localize specific mRNAs within tissue samples.  In this context, it can help define the spatial-temporal patterns of gene expression within cells and tissues.

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