Evidence (see P.G. Shiels, A.J. Kind, K.H. Campbell, et al. (1999) Analysis of telomere lengths in cloned sheep. Nature 399, 316-17) suggested that Dolly may have been "genetically older" than her actual age would have suggested. 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 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 a sheep that was significantly older, say, 9 or 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 a mammary cell was fused with an oocyte.)
A. Suggest an explanation for why Dolly's chromosomes seemed so old.
B. Let's suppose that Dolly at age 11 gave birth to a lamb named Molly; Molly was produced naturally (by mating Dolly with a normal male). 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.

Discuss the advantages and disadvantages of gene therapy. Because a limited amount of funding is available for gene therapy research, make a priority list of the three top diseases for which you would fund research. Discuss your choices.

Recombinant bacteria can produce hormones that are normally produced in humans. Briefly describe how this is accomplished.

Discuss the advantages and disadvantages of gene therapy. Because a limited amount of funding is available for gene therapy research, make a priority list of the three top diseases for which you would fund research. Discuss your choices.

For centuries, people have searched for the fabled Fountain of Youth, said to confer the ability to forestall old age and remain young forever. To gain insight into how tackling aging by targeting telomerase might work, researchers looked at mice that lack a telomerase gene. These mice have shorter telomeres than normal mice and age prematurely. But when these mice are engineered to express telomerase in their somatic cells, their telomeres lengthen, and the effects of aging are reversed. This observation suggests that a drug that stimulates the expression of telomerase in somatic cells could prevent telomere shortening and stop the aging process. Do you think such a drug would work well in humans? What might be some potential side effects of such a drug?

Each of the lettered choices below refers to the following numbered statements. Select the best lettered choice. A choice may be used once, more than once, or not at all. (A) Synapse (B) Myelin sheath (C) cerebrum (D) Cerebellum (E) Somatic nervous sytem. 3. Gap between two neurons.

Although genetic recombination events are important for generating significant diversity in the antigen-binding site of Igs, post-recombination somatic events may be even more important in achieving overall Ig diversity. Do you agree or disagree with this statement? Explain.

Choose the letter of the best answer. A scientist studying the brain is studying part of the A. peripheral nervous system. B. somatic nervous system. C. autonomic nervous system. D. central nervous system.

The somatic nervous system contains nerves that run from the central nervous system to the (1) muscles of the skeleton (2) heart (3) smooth muscles of the gastrointestinal tract (4) endocrine glands

Choose the letter of the correct term or concept below to complete the sentence. a. neurotransmitters b. somatic nervous system c. autonomic nervous system d. hormones e. midbrain f. hindbrain g. pituitary gland h. synapse i. identical twins j. fraternal twins. The __________ is the part of the brain that integrates sensory information.

Use the following terms to fill in the blank.

metaphase

DNA replication

somatic cells

$\mathrm{G}_2$ phase

telophase

mitosis

cytokinesis

$\mathrm{G}_1$ phase

Division of the cytoplasm into two distinct new cells involves a separate process known as ______.

Use the following terms to fill in the blank.

metaphase

DNA replication

somatic cells

$\mathrm{G}_2$ phase

telophase

mitosis

cytokinesis

$\mathrm{G}_1$ phase

The cell cycle includes 2 major stages:

a. Interphase

b. ______

Discuss the following problem. With age, somatic cells are thought to accumulate genomic “scars” as a result of the inaccurate repair of double-strand breaks by nonhomologous end joining (NHEJ). Estimates based on the frequency of breaks in primary human fibroblasts suggest that by age 70, each human somatic cell may carry some 2000 NHEJ-induced mutations due to inaccurate repair. If these mutations were distributed randomly around the genome, how many protein- coding genes would you expect to be affected? Would you expect cell function to be compromised? Why or why not? (Assume that 2% of the genome-1.5% protein-coding and 0.5% regulatory-is crucial information.)

Use the following terms to fill in the blank.

metaphase

DNA replication

somatic cells

$\mathrm{G}_2$ phase

telophase

mitosis

cytokinesis

$\mathrm{G}_1$ phase

In S phase, the cell duplicates its chromosomes. This involves _______ and the synthesis of histones and other proteins in the nucleus.