Which of the following describes a difference between how monozygotic and dizygotic twins develop?

• A. Monozygotic twins always share the same placenta, whereas dizygotic twins never share a placenta.
• B. Monozygotic twins are always of the same sex, while dizygotic twins are always of different sexes.
• C. Monozygotic twins have different genetic material, whereas dizygotic twins have identical genetic material.
• D. Monozygotic twins develop from a single fertilized egg that splits, while dizygotic twins develop from two separate fertilized eggs.

Answer: (D)

Verified step by step guidance

1. Understand the basic definitions: Monozygotic twins, also known as identical twins, originate from a single fertilized egg that splits into two embryos. Dizygotic twins, or fraternal twins, develop from two separate eggs fertilized by two different sperm cells.
2. Consider the genetic implications: Monozygotic twins share identical genetic material because they come from the same fertilized egg. In contrast, dizygotic twins have different genetic material, similar to regular siblings, because they come from two separate eggs.
3. Examine the placental development: Monozygotic twins may share a placenta or have separate placentas depending on when the fertilized egg splits. Dizygotic twins always have separate placentas because they develop from separate eggs.
4. Analyze the sex of the twins: Monozygotic twins are always of the same sex because they originate from the same fertilized egg with identical genetic material. Dizygotic twins can be of the same or different sexes since they come from two different eggs.
5. Summarize the key difference: The primary distinction between monozygotic and dizygotic twins is their origin. Monozygotic twins come from a single fertilized egg that splits, while dizygotic twins develop from two separate fertilized eggs.