论文部分内容阅读
人类双胞胎的形成有以下两种类型:①由一个受精卵在囊胚期分成两个内细胞群而发育成两个胎儿者为同卵双胞胎。这种分裂产生的孪生子具有相同的遗传特征,因此,性别相同,性格和容貌酷似。②由两个卵细胞同时受精并发育长大而成两个胎儿者为异卵双胎,大多数双胞胎(约75%)属此。由于他们是由两个不同的受精卵发育的,故具有不同的遗传特性,性格和容貌的相似性也就逊于前者。后一种孪生子可能是同一性别,也可能是不同性别。人口学和医学的研究表明,同卵双胞胎的出生频度相当稳定,地域间、人种间,
The formation of human twins in the following two types: ① from a fertilized egg in the blastocyst stage is divided into two inner cell groups and develop into two fetuses were identical twins. This split twins have the same genetic traits, therefore, they are the same in gender, character and appearance. ② by the two eggs at the same time fertilize and grow into two fetuses were fraternal twins, most twins (about 75%) belong to this. Because they are developed by two different fertilized eggs, they have different genetic traits, similarities in personality and appearance than the former. The latter twin may be of the same gender or may be of different genders. Demographic and medical studies have shown that identical twins have a fairly steady frequency of births, interracial, interracial,