Chapter 22, Problem 8EQ

Evidence [see P. G. Shiels, A. J. Kind, K. H. Campbell, et al. (1999), “Analysis of telomere lengths in cloned sheep,”  Nature 399, 316–317] suggests that Dolly may have been genetically older than her actual age. As mammals age, the chromosomes in somatic cells tend to shorten from the telomeres. Therefore, older individuals have shorter chromosomes in their somatic cells than do younger ones. When researchers analyzed the chromosomes in the somatic cells of Dolly when she was about 3 years old, the lengths of her chromosomes were consistent with those of a sheep that was significantly older, say, 9–10 years old. (Note: As described in the chapter, the sheep that donated the somatic cell that produced Dolly was 6 years old, and her mammary cells had been grown in culture for several cell doublings before one of the cells was fused with an oocyte.)

A. Suggest an explanation why Dolly’s chromosomes seemed older than they should have been.

B. Let’s suppose that a female sheep (like Dolly), which was produced via reproductive cloning, was mated at age 11 to a normal male sheep and then gave birth to a lamb named Molly. When Molly was 8 years old, a sample of somatic cells was analyzed. How old would you expect Molly’s chromosomes to appear, based on the phenomenon of telomere shortening? Explain your answer.

C. Discuss how the observation of chromosome shortening, which was observed in Dolly, might affect the popularity of reproductive cloning.