200702061046曼赤肯為什麼腳這麼短?

對阿...為什麼這麼短??
有人說曼赤肯的短腿是人工育種後的結果?
錯!!!!!!
人類才沒有這麼大的能耐,這種特徵是由一對影響骨骼成長賀爾蒙的基因所決定的
是自然發生的喔!
曼赤肯可能會生出短腿的寶寶,但也有可能生出一般長腿貓。
這一篇文章是從Wikipedia摘錄下來的,解釋曼赤肯的基因組合
http://en.wikipedia.org/wiki/Munchkin_(cat)
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基因

曼赤肯基因是一個常染色體顯性基因。目前為止,沒有任何一隻貓身上帶有同型結合的曼赤肯基因 (也就是說,貓帶有一對曼赤肯基因 MM,分別來自於父輩與母輩),原因是同型結合的受精卵並無法存活下來。擁有異型結合的曼赤肯基因的貓 (Mm,從上一代得到一個曼赤肯基因M,以及一個一般的基因m)
因為唯有異型結合的仔貓能存活下來,因此在曼赤肯貓的繁殖中,每一胎可能全都是短腿特徵,可能只有部分短腿,或甚至完全都是長腿。這種現象即使在兩隻同為曼赤肯的結合的情況下也是一樣。

曾經有理論指出這樣的短腿基因是位於造成人類軟骨發育不全的相同基因位置上,然而至今沒有學術研究能證明這個理論。一般相信這是一種相當於侏儒基因(hypochondroplasia)所造成的,但比起真正的侏儒基因的效果更加輕微。侏儒基因不只造成腿部骨骼短小。曼赤肯貓腿部比起其他家貓更加的短小,但在其他方面在基因、大小、外觀上是完全一樣的。

 

基因圖

M代表顯性曼赤肯基因,m代表隱性正常基因,這裡用基因圖來表達短腿仔貓出生的機率。

 

帶有一對曼赤肯基因的受精卵 (MM) 將無法存活,在懷孕階段就會無法成長,然後被母體吸收。帶有一個曼赤肯基因跟一個隱性基因的仔貓 (Mm) 將會是標準型的曼赤肯。帶有一對正常基因 (mm) 的仔貓則是正常。Mm的曼赤肯貓有能力傳達這種基因給他的子代。一般的mm仔貓則沒有這種基因。

 

曼赤肯貓 X 曼赤肯貓

在這個組合下出生的仔貓,有25%機會無法出生(MM)25%機會會成為一般正常貓(mm),有50%機會會成為標準型曼赤肯(Mm)

 

曼赤肯X 一般貓

這種組合下出生的仔貓,有50%的機率會成為標準型曼赤肯,有50%機會成為一般貓。

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Genetics

The munchkin gene is an autosomal dominant one. Thus far to date, there have been no viable kittens that are homozygous for the munchkin gene (that is, kittens with two copies of the munchkin gene, one from each parent), possibly because of gene lethality. Kittens that are heterozygous for the munchkin gene (that is, a munchkin gene from one parent and a normal gene from the other) will be 'standard' munchkins.

Because only heterozygous munchkin cats survive to pass on the gene, all litters with at least one munchkin parent have the possibility of having all munchkin kittens, all normal kittens, or a combination of munchkins and normal kittens. A litter with two munchkin parents may be all munchkin kittens, all normal kittens, all non-viable kittens with two copies of the munchkin gene, or any combination of the three.

At one time it was theorized that this short legged trait was due to the same locus of genes that cause achondroplasia in humans, however all attempts to prove this to date, have failed. It is now believed to be the equivalent of hypochondroplasia which is much milder than achondroplasia. Achondroplasia affects more than the long bones of the legs. The munchkin cat is shorter than a standard domestic, but in all other respects it is identical, genetically and in size and overall appearance.

Punnett squares

Punnett squares, in which the M represents the dominant munchkin gene and the m represents the recessive normal gene, may be used to illustrate the chances of a particular mating resulting in a munchkin cat.

Kittens bearing two copies of the munchkin gene (MM) will not survive. Kittens bearing one munchkin gene and one normal gene (Mm) will be munchkins. Kittens bearing two normal genes (mm) will be normal. Mm munchkin kittens will be able to pass on the munchkin gene to their own offspring. Normal mm kitten will not, as it does not have that gene.

For each kitten born from this mating, there is a 25% chance it will be non-viable, a 25% chance it will be normal, and a 50% chance it will be a munchkin.

For each kitten born from this mating, there is a 0% chance it will be non-viable (unless it has a different, unrelated condition), a 50% chance it will be normal, and a 50% chance it will be a munchkin.

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