Life: The Science of Biology, Ninth Edition
Sadava • Hillis • Heller • Berenbaum
Working with Data
Cloning a Mammal
(Textbook Figure 19.4)
Introduction
In 1996, Ian Wilmut and colleagues announced
the first successful cloning of a mammal as a
result of a technique known as somatic cell
nuclear transfer (SCNT). Briefly, mammary
cells were removed from a Dorset sheep, and an
unfertilized egg was removed from a Scottish
blackface ewe. The nucleus of a mammary cell,
which was in the G2 phase of the cell cycle, was
fused with the enucleated egg from the Scottish
blackface ewe. The resulting cell was stimulated
to divide and form into an early embryo, which
was transplanted into a second Scottish
blackface ewe. The embryo developed and the
ewe gave birth to Dolly, a Dorset sheep
genetically identical to the sheep from which the
donor mammary cells were obtained. These
results demonstrated that, under appropriate
circumstances, animal cells are totipotent. Aside
from a number of ethical issues surrounding the
idea of cloning mammals, use of the SCNT
technique itself also raises other scientific and
medical concerns, including the possibility of
the risk of premature aging. Initially, Dolly appeared to be a healthy sheep, but over time
she developed severe arthritis, a condition usually associated with older animals. In 1999,
research published in the journal Nature suggested that Dolly may have been susceptible
to premature aging due to the shortened telomeres in her cells. Dolly was euthanized at
the age of 6 years old, approximately half of the normal life span of a sheep.
© 2011 Sinauer Associates, Inc.
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Original Paper
Wilmut, I., A. E. Schnieke, J. McWhir, A. J. Kind, and K. H. S. Campbell. 1997. Viable
offspring derived from fetal and adult mammalian cells. Nature 385: 810–813.
http://www.nature.com/nature/journal/v385/n6619/pdf/385810a0.pdf
Links
National Institutes of Health: Office of Science Education: Research in the News:
Creating a Cloned Sheep Named Dolly
http://science.education.nih.gov/home2.nsf/Educational+ResourcesTopicsGenetics/BC50
86E34E4DBA0085256CCD006F01CB
BBC News: Cloned sheep Dolly has arthritis
http://news.bbc.co.uk/1/hi/sci/tech/1741559.stm
CNN.com: First cloned sheep Dolly dies at 6
http://www.cnn.com/2003/WORLD/europe/02/14/cloned.dolly.dies/
The University of Utah: Learn.Genetics: Genetic Science Learning Center: What is
Cloning?
http://learn.genetics.utah.edu/units/cloning/whatiscloning/
PubMedCentral: Reproductive Biology and Endocrinology: Will cloned animals suffer
premature aging—The story at the end of clones’ chromosomes
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=305328
Analyze the Data
© 2011 Sinauer Associates, Inc.
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Question 1
The team that cloned Dolly the sheep, derived from a mammary epithelium cell, also
attempted cloning by transplanting nuclei from fetal fibroblasts and embryos. The results
are shown in Table 1. Trace the percent survival of the fused cells from fusion to birth.
What can you conclude about the efficiency of this cloning process?
Question 2
Compare the efficiencies of cloning using nuclear donors from different sources. What
can you conclude about the ability of different nuclei to be reprogrammed?
Question 3
The normal gestation times for lambs are Finn Dorset: 143 days; Black Welsh: 147 days;
and Poll Dorset: 145 days. Birth weights for the three breeds are 3–9 kg. The data for the
cloned sheep are shown in Table 2. What can you conclude about gestation and birth
weight of cloned lambs?
© 2011 Sinauer Associates, Inc.
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Figure 1
Question 4
To examine the genetics of the cloned animals, DNA polymorphic markers were
analyzed. These DNA fragments have different sizes on gel electrophoresis, depending
on genotype. DNA from recipient sheep (not the nuclear donors, but the surrogate
mothers that carried the embryos) was compared to DNA from donor cells and newborn
lambs of the nuclear donors, embryo cells (SEC1), fetal cells (BLWF1) and mammary
cells (OME). Figure 1 shows photographs of the gels for two gene markers, FCB 11 and
FCB 304. Which gels show that the genotypes of the lambs are the same as their cell
donors?
Question 5
Which gels show that the genotypes of the lambs are different than their recipient
mothers?
© 2011 Sinauer Associates, Inc.
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