[Campbell Biology P.479] The passage states that cloned animals often exhibit defects and th... | Practice Question

The passage states that cloned animals often exhibit defects and that the efficiency of cloning is low. Which of the following best explains a major reason for the low success rate and abnormalities observed in cloned animals?

  • A: The donor nucleus always comes from an embryonic stem cell, which is difficult to manipulate.
  • B: Cloned animals are susceptible to random X chromosome inactivation, leading to phenotypic variations but not defects.
  • C: The nuclear transfer procedure cannot fully reverse the epigenetic modifications in the differentiated donor nucleus, such as abnormal DNA methylation patterns.
  • D: Environmental factors during development significantly alter the genetic code of the cloned embryo.

Explanation

The text explains that the low efficiency and high incidence of abnormalities in cloned animals are due to the inability of the nuclear transfer procedure to fully reverse epigenetic changes like DNA methylation and histone acetylation in the differentiated donor nucleus. These epigenetic marks interfere with proper gene expression necessary for normal embryonic development.