8800 skrev:http://lmgtfy.com/?q=chromosome+21+downs+syndrome


http://www.ds-health.com/trisomy.htm

Jeg skal som sagt ikke bare vide at det er kromosom 21... men hvorfor kromosom 21, er så vigtig iforhold til dannelsen af Downs syndrom. (Hvad sker der biologisk set?) Jeg er ikke sikker på at biologerne selv ved et? Altså man kan undre sig lidt over at, med et kromosom 21 er man mormal, men med to sæt nr. 21 kromosomer bliver man handicappet?

The 21st Chromosome and Down Syndrome
The chromosomes are holders of the genes, those bits of DNA that direct the production of a wide array of materials the body needs. This direction by the gene is called the gene's "expression." In trisomy 21, the presence of an extra set of genes leads to overexpression of the involved genes, leading to increased production of certain products. For most genes, their overexpression has little effect due to the body's regulating mechanisms of genes and their products. But the genes that cause Down syndrome appear to be exceptions.

Which genes are involved? That's been the question researchers have asked ever since the third 21st chromosome was found. From years of research, one popular theory stated that only a small portion of the 21st chromosome actually needed to be triplicated to get the effects seen in Down syndrome; this was called the Down Syndrome Critical Region. However, this region is not one small isolated spot, but most likely several areas that are not necessarily side by side. The 21st chromosome may actually hold 200 to 250 genes (being the smallest chromosome in the body in terms of total number of genes); but it's estimated that only a small percentage of those may eventually be involved in producing the features of Down syndrome. Right now, the question of which genes do what is highly speculative. However, there are some suspects.

Genes that may have input into Down syndrome include:

Superoxide Dismutase (SOD1)-- overexpression may cause premature aging and decreased function of the immune system; its role in Senile Dementia of the Alzheimer's type or decreased cognition is still speculative
COL6A1 -- overexpression may be the cause of heart defects
ETS2 -- overexpression may be the cause of skeletal abnormalities
CAF1A -- overexpression may be detrimental to DNA synthesis
Cystathione Beta Synthase (CBS) -- overexpression may disrupt metabolism and DNA repair
DYRK -- overexpression may be the cause of mental retardation
CRYA1 -- overexpression may be the cause of cataracts
GART -- overexpression may disrupt DNA synthesis and repair
IFNAR -- the gene for expression of Interferon, overexpression may interfere with the immune system as well as other organ systems
Other genes that are also suspects include APP, GLUR5, S100B, TAM, PFKL, and a few others. Again, it is important to note that no gene has yet been fully linked to any feature associated with Down syndrome.

One of the more notable aspects of Down syndrome is the wide variety of features and characteristics of people with trisomy 21: There is a wide range of mental retardation and developmental delay noted among children with Down syndrome. Some babies are born with heart defects and others aren't. Some children have associated illnesses such as epilepsy, hypothyroidism or celiac disease, and others don't. The first possible reason is the difference in the genes that are triplicated. As I mentioned above, genes can come in different alternate forms, called "alleles." The effect of overexpression of genes may depend on which allele is present in the person with trisomy 21. The second reason that might be involved is called "penetrance." If one allele causes a condition to be present in some people but not others, that is called "variable penetrance," and that appears to be what happens with trisomy 21: the alleles don't do the same thing to every person who has it. Both reasons may be why there is such variation in children and adults with Down syndrome.

Kazon skrev:

8800 skrev:http://lmgtfy.com/?q=chromosome+21+downs+syndrome


http://www.ds-health.com/trisomy.htm

Jeg skal som sagt ikke bare vide at det er kromosom 21... men hvorfor kromosom 21, er så vigtig iforhold til dannelsen af Downs syndrom. (Hvad sker der biologisk set?) Jeg er ikke sikker på at biologerne selv ved et? Altså man kan undre sig lidt over at, med et kromosom 21 er man mormal, men med to sæt nr. 21 kromosomer bliver man handicappet?

Starforker skrev:

Jeg skal som sagt ikke bare vide at det er kromosom 21... men hvorfor kromosom 21, er så vigtig iforhold til dannelsen af Downs syndrom. (Hvad sker der biologisk set?) Jeg er ikke sikker på at biologerne selv ved et? Altså man kan undre sig lidt over at, med et kromosom 21 er man mormal, men med to sæt nr. 21 kromosomer bliver man handicappet?

Man er næppe "normal", hvis man kun har ét kromosom 21, da man gerne skulle have et stk. fra hver forældre. Den hyppigste form for Downs syndrom er, som du også var inde på, trisomi 21 (trisomi = tre = et ekstra kromosom nr. 21.
Hvis dit spørgsmål er, hvad der rent biologisk gør, at et ekstra kromosom giver symptomerne ved Downs syndrom, mener man bare det er en overeksponering af gener.

8800 skrev:

Kazon skrev:

8800 skrev:http://lmgtfy.com/?q=chromosome+21+downs+syndrome


http://www.ds-health.com/trisomy.htm

Jeg skal som sagt ikke bare vide at det er kromosom 21... men hvorfor kromosom 21, er så vigtig iforhold til dannelsen af Downs syndrom. (Hvad sker der biologisk set?) Jeg er ikke sikker på at biologerne selv ved et? Altså man kan undre sig lidt over at, med et kromosom 21 er man mormal, men med to sæt nr. 21 kromosomer bliver man handicappet?

Så beklager jeg det lettere flabede første link, men håber alligevel at du kan bruge tjr's udlægning til noget