Final answer:
Identical twins look alike because they develop from the same fertilized egg, meaning they inherited copies of the same chromosomes and have all the same genes. Genes are the units of heredity that determine our traits, and they are made possible by nucleic acids.
Step-by-step explanation:
Identical twins look alike because they develop from the same fertilized egg, meaning they inherited copies of the same chromosomes and have all the same genes. Genes are the units of heredity that determine our traits, and they are made possible by nucleic acids, specifically DNA and RNA. These nucleic acids consist of small units called nucleotides, which bind together to form chains. Therefore, the correct answer is option 3) Because their bodies contain identical nucleic acids.