In humans, identical twins are possible because a. extraembryonic cells interact with the zygote nucleus. b. convergent extension occurs. c. early blastomeres can form a complete embryo if isolated. d. the gray crescent divides the dorsal-ventral axis into new cells.

Verified step by step guidance

1. Identify the key concept: The question is asking about the biological mechanism that allows for the formation of identical twins in humans.
2. Understand the options: Each option represents a different developmental biology concept or process.
3. Analyze the correct option: Identical twins occur when early blastomeres (cells from the initial divisions of the fertilized egg) have the potential to individually develop into a complete embryo if they are separated.
4. Eliminate incorrect options: Options a, b, and d describe other developmental processes that do not directly explain the formation of identical twins.
5. Select the correct answer: The correct answer is c. early blastomeres can form a complete embryo if isolated, as this describes the ability of early embryonic cells to independently develop into a full organism, leading to the formation of identical twins.

Key Concepts

Identical Twins Formation

Identical twins, or monozygotic twins, form when a single fertilized egg (zygote) splits into two separate embryos during the early stages of development. This process occurs after the zygote undergoes several rounds of cell division, leading to the formation of blastomeres, which can develop into two genetically identical individuals.

Blastomeres and Embryonic Development

Blastomeres are the cells produced by the division of the zygote. In the early stages of embryonic development, these cells are totipotent, meaning they have the potential to develop into a complete organism. If isolated, early blastomeres can still form a complete embryo, which is a key factor in the formation of identical twins.

Embryonic Cell Interaction

During early embryonic development, cells communicate and interact with each other, influencing their fate and organization. This interaction is crucial for proper development, as it helps establish the body plan and ensures that cells differentiate into the appropriate tissues. However, in the context of identical twins, the ability of isolated blastomeres to develop independently is more relevant than cell interaction with the zygote nucleus.