急!!關於唐氏綜合症!不是問基本資料.

it's the definition of the disease. if there's an extra chromosome 21, then it's called Down's syndrome. there're other names for other abnoramilties in other chromosomes, e.g. turner syndrome for lacking one X chromosome.
chromosome 21 is the shortest chromosone og human genome, therefore an additional chromosome 21 will give the least impact than any other extra chromosome. if there's an extra chromosome for other chromosomes, they baby will not be able to sruvive before birth as it'll have too severe abnormalities.
mice will not have down's syndrome because it has different number of chromosomes from human's.

There are somethings have to be clarified. First of all, there was a clinical characteristics of that syndrome discovered by Down and after that this diseased was named after his. Afterwards, people firstly proved that this syndrome was related to extra human chromosome number 21. Trisomy 21 (Ts21) is the most common live-born human aneuploidy that will manifest Down syndrome (DS). However, Down syndrome is not solely caused by Trisomy 21, for example, overexpression of certain gene(s) on Chr 21, translocation of genes on Chr 21(that is, transfer of genes from one chr. to other chr.), however, up till this moment, the abnormalities occurs on Chr 21 and we cannot exclude the chance that other genetic anomalism may sooner or later to be discovered to be related to this syndrome.

Besides, mouse won't naturally develop DS, however, man made DS can be used as mouse model to investigate the DS by gene transfer.

之前位仁兄都答晒d基本問題,病原角度真係要chromosome21多一條先至會有,正如心臟病一定係心臟有事先至有,其他chromosome樹多左呢,可能會個baby腰拆,但好似chromosome23即係x &y chromosome樹多左既話,係會出現叫polymorphism既病症,例如xx加y,出現中性人(有女性性器官加男性性徵,即係陰核會大到好似penis咁)xxx即baby就會正常表徵,但就有遺傳畀下一代既risk啦,其他生物多左chromosome未必係病徵,有時係evolution既表現,即係多左係好事,insects就係好例子