Monozygotic twins - what cause phenotype difference?

Twins are two offspring produced by the same pregnancy. Twins can either be monozygotic (“identical“), meaning that they develop from one zygote that splits and forms two embryos, or dizygotic (“fraternal“), meaning that they develop from two eggs, each fertilized by separate sperm cells. In contrast, a fetus which develops alone in the womb is called a singleton, and the general term for one offspring of a multiple birth is multiple Zygosity[edit] Zygosity is the degree of identity in the genome of twins. There are five common variations of twinning. The three most common variations are all dizygotic (fraternal):[14] Male--female twins are the most common result, 50 percent of dizygotic twins and the most common grouping of twins. Female--female dizygotic twins (sometimes called “sororal twins“) Male--male dizygotic twins The other two variations are monozygotic (“identical“) twins: Female--female monozygotic twins Male--male monozygotic twins (less common) Among non-twin births, male singletons are slightly (about five percent) more common than female singletons. The rates for singletons vary slightly by country. For example, the sex ratio of birth in the US is males/female, while it is males/female in Italy. However, males are also more susceptible than females to die in utero, and since the death rate in utero is higher for twins, it leads to female twins being more common than male twins. #Eukaryotic #GeneticsExamQuestionsSolutions #chromosome #alleles #Proteins #DNA #GeneticExamQuestionsSolutions #genes #Genetics101 #MolecularBiology #phenotype #geneticCode #geneExpression #Genetics #centromeres #Cancer #genotype #gene #GeneticsLecture