Final answer:
Identical twins possess identical genotypes because they originate from the same fertilized egg but can have variable phenotypes due to the influence of different environmental factors on gene expression.
Step-by-step explanation:
Two identical twins raised in different environments will possess identical genotypes and variable phenotypes. Genotype refers to the genetic makeup of an organism, the information encoded in its DNA. Since identical twins come from the same fertilized egg, they have identical genotypes. However, the phenotype is the observable expression of the genotype and can vary greatly due to different environmental influences. For instance, changes in gene expression as a result of different environments can lead to different phenotypes, even among individuals with the same genotype, such as identical twins.
Epigenetics studies these variations and shows how the same genetic information can give rise to different characteristics. While identical twins share the same genes, the manifestation of those genes, their phenotypes, can differ significantly based on factors such as lifestyle, diet, and exposure to diseases - contributing to variable phenotypes. An example of this could be one twin developing a disease while the other does not, despite their identical genetic make-up.