Stem cells have very long telomeres due to their high telomerase activity, allowing them to proliferate indefinitely in a controlled manner. In contrast, most terminally differentiated adult somatic cells (eg, myocardial cells, neurons, pancreatic~ cells) have short telomeres as they do not express telomerase and their telomeres shorten with every cell division (Choices C, D, and E). Critical shortening in telomere length is thought to be a signal for programmed cell death. In fact, syndromes of premature aging (eg, Bloom syndrome) are associated with shortened telomeres. In contrast, cancer cells upregulate their telomerase activity, preventing cell death by maintaining their telomere length.
(Choice B) Erythrocytes have no nuclei and therefore have no potential to divide.

(Choice A) DNA methylation silences gene transcription so that the affected protein would be completely absent. A pathologic example of DNA methylation is the inhibition of tumor suppressor genes as a mechanism for cancer development.
(Choice C) A defect in protein folding, as seen with the CFTR protein in cystic fibrosis, would result in abnormal protein functioning. Protein concentration may be normal or low due to more rapid degradation of the abnormal protein.
(Choices D and E) Splicing mutations can result in inappropriate removal of exons or persistence of intrans; this creates aberrant mRNA that is presented for translation and results in production of an abnormal protein. Similarly, a defect in translation results in insufficient or abnormal protein synthesis, which is reflected both in the serum and intracellularly.

(Choice B) If the mother had a failure in meiosis II, the child’s RFLP analysis would reveal only two bands (see example). There would be a single band from the father and a darker, thicker band from the mother. The darker, thicker band signifies the inheritance of both sister chromatids, which wi ll produce equal-size restriction fragments (but twice the normal amount).
(Choice C) If the father had a failure in meiosis I, the child’s RFLP analysis would reveal 3 bands (see example). In this instance, there would be a single band inherited from the mother with two bands inherited from the father.
(Choice D) If the father had a failure in meiosis II, the child’s RFLP analysis would reveal two bands (see example). In this instance, there would be a single band inherited from the mother and a second band from the father. The father’s band would be darker and thicker, signifying the inheritance of both sister chromatids.