A discussion of Weinberg's rule on the zygosity of twins.
D000328:Adult; D000367:Age Factors; D005260:Female; D005306:Fertilization; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008433:Mathematics; D010063:Ovum; D011247:Pregnancy; D012744:Sex Ratio; D014427:Twins