Download White Skin.” Answer the questions to help you write your summary

Anatomy/Physiology I Name ________________________________ ____/15 (see rubric) Per. _________ Goals: 1. Understand how and why human skin color varies amongst populations. 2. Understand the importance of skin color to the formation of vitamin D and the homeostasis of the skeletal system. 3. Summarize and evaluate articles, videos, and text. Directions: Read the rubric. Read the article: “Scientists Find A DNA Change That Accounts For
White Skin.” Answer the questions to help you write your summary. Write both a summary and an opinion paragraph and list the source information in the following format: Author, “Title of Article,” Magazine or Newspaper Source, date. Questions: 1. Describe the DNA change that was discovered that may be linked to skin‐whitening. 2. Why do scientists think that white skin was beneficial to humans that migrated north? 3. What did scientists discover about Asian skin color? 4. Describe the organism used to discover this gene. What characteristic was affected in this species by this gene? 5. In which other species did scientists locate this gene? 6. How is skin color determined? 7. What is the “name” of this gene? Is it believed to be the only gene responsible for skin color? Explain. 8. Describe the importance of sunlight and Vitamin D to the human body. 9. What are some practical spinoffs of this discovery? 10. How might this gene discovery affect the debate over the biological significance of race? How do most geneticists feel about the concept of “race?” Scientists Find A DNA Change That Accounts For White
Skin
By Rick Weiss
Washington Post Staff Writer
Friday, December 16, 2005; A01
Scientists said yesterday that they have discovered a tiny genetic mutation that largely explains
the first appearance of white skin in humans tens of thousands of years ago, a finding that helps
solve one of biology's most enduring mysteries and illuminates one of humanity's greatest
sources of strife.
The work suggests that the skin-whitening mutation occurred by chance in a single individual
after the first human exodus from Africa, when all people were brown-skinned. That person's
offspring apparently thrived as humans moved northward into what is now Europe, helping to
give rise to the lightest of the world's races.
Leaders of the study, at Penn State University, warned against interpreting the finding as a
discovery of "the race gene." Race is a vaguely defined biological, social and political concept,
they noted, and skin color is only part of what race is -- and is not.
In fact, several scientists said, the new work shows just how small a biological difference is
reflected by skin color. The newly found mutation involves a change of just one letter of DNA
code out of the 3.1 billion letters in the human genome -- the complete instructions for making a
human being.
"It's a major finding in a very sensitive area," said Stephen Oppenheimer, an expert in
anthropological genetics at Oxford University, who was not involved in the work. "Almost all
the differences used to differentiate populations from around the world really are skin deep."
The work raises a raft of new questions -- not least of which is why white skin caught on so
thoroughly in northern climes once it arose. Some scientists suggest that lighter skin offered a
strong survival advantage for people who migrated out of Africa by boosting their levels of
bone-strengthening vitamin D; others have posited that its novelty and showiness simply made it
more attractive to those seeking mates.
The work also reveals for the first time that Asians owe their relatively light skin to different
mutations. That means that light skin arose independently at least twice in human evolution, in
each case affecting populations with the facial and other traits that today are commonly regarded
as the hallmarks of Caucasian and Asian races.
Several sociologists and others said they feared that such revelations might wrongly overshadow
the prevailing finding of genetics over the past 10 years: that the number of DNA differences
between races is tiny compared with the range of genetic diversity found within any single racial
group.
Even study leader Keith Cheng said he was at first uncomfortable talking about the new work,
fearing that the finding of such a clear genetic difference between people of African and
European ancestries might reawaken discredited assertions of other purported inborn differences
between races -- the most long-standing and inflammatory of those being intelligence.
"I think human beings are extremely insecure and look to visual cues of sameness to feel better,
and people will do bad things to people who look different," Cheng said.
The discovery, described in today's issue of the journal Science, was an unexpected outgrowth of
studies Cheng and his colleagues were conducting on inch-long zebra fish, which are popular
research tools for geneticists and developmental biologists. Having identified a gene that, when
mutated, interferes with its ability to make its characteristic black stripes, the team scanned
human DNA databases to see if a similar gene resides in people.
To their surprise, they found virtually identical pigment-building genes in humans, chickens,
dogs, cows and many others species, an indication of its biological value.
They got a bigger surprise when they looked in a new database comparing the genomes of four
of the world's major racial groups. That showed that whites with northern and western European
ancestry have a mutated version of the gene.
Skin color is a reflection of the amount and distribution of the pigment melanin, which in
humans protects against damaging ultraviolet rays but in other species is also used for
camouflage or other purposes. The mutation that deprives zebra fish of their stripes blocks the
creation of a protein whose job is to move charged atoms across cell membranes, an obscure
process that is crucial to the accumulation of melanin inside cells.
Humans of European descent, Cheng's team found, bear a slightly different mutation that hobbles
the same protein with similar effect. The defect does not affect melanin deposition in other parts
of the body, including the hair and eyes, whose tints are under the control of other genes.
A few genes have previously been associated with human pigment disorders -- most notably
those that, when mutated, lead to albinism, an extreme form of pigment loss. But the newly
found glitch is the first found to play a role in the formation of "normal" white skin. The Penn
State team calculates that the gene, known as slc24a5, is responsible for about one-third of the
pigment loss that made black skin white. A few other as-yet-unidentified mutated genes
apparently account for the rest.
Although precise dating is impossible, several scientists speculated on the basis of its spread and
variation that the mutation arose between 20,000 and 50,000 years ago. That would be consistent
with research showing that a wave of ancestral humans migrated northward and eastward out of
Africa about 50,000 years ago.
Unlike most mutations, this one quickly overwhelmed its ancestral version, at least in Europe,
suggesting it had a real benefit. Many scientists suspect that benefit has to do with vitamin D,
made in the body with the help of sunlight and critical to proper bone development.
Sun intensity is great enough in equatorial regions that the vitamin can still be made in darkskinned people despite the ultraviolet shielding effects of melanin. In the north, where sunlight is
less intense and cold weather demands that more clothing be worn, melanin's ultraviolet
shielding became a liability, the thinking goes.
Today that solar requirement is largely irrelevant because many foods are supplemented with
vitamin D.
Some scientists said they suspect that white skin's rapid rise to genetic dominance may also be
the product of "sexual selection," a phenomenon of evolutionary biology in which almost any
new and showy trait in a healthy individual can become highly prized by those seeking mates,
perhaps because it provides evidence of genetic innovativeness.
Cheng and co-worker Victor A. Canfield said their discovery could have practical spinoffs. A
gene so crucial to the buildup of melanin in the skin might be a good target for new drugs against
melanoma, for example, a cancer of melanin cells in which slc24a5 works overtime.
But they and others agreed that, for better or worse, the finding's most immediate impact may be
an escalating debate about the meaning of race.
Recent revelations that all people are more than 99.9 percent genetically identical has proved that
race has almost no biological validity. Yet geneticists' claims that race is a phony construct have
not rung true to many nonscientists -- and understandably so, said Vivian Ota Wang of the
National Human Genome Research Institute in Bethesda.
"You may tell people that race isn't real and doesn't matter, but they can't catch a cab," Ota Wang
said. "So unless we take that into account it makes us sound crazy."
© 2005 The Washington Post Company
“Reading and Reflecting” Rubric CRITERIA Summary _____/4 Evaluation/Opinion _____/4 Mechanics _____/2 BASIC 1 APPROACHING 2 MEETING 3 More than two major points Concise and accurate but one Concise, accurate, and missed and either too wordy, or two major points of complete—no major points too brief or inaccurate. reading are missed. of reading are missed. OR No major points missed but either too wordy, too brief or inaccurate. Student opinion of reading Student opinion of reading Student opinion of reading does not address the content addresses the content and addresses the content and or objectives of the objectives of assignment. objectives of assignment and assignment. includes references to specific examples from the reading. More than 2 errors in grammar, spelling AND source info missing. ___/3 Questions or guided information included. ____/15 Total Points One or two errors in grammar, spelling OR source info missing. Correct grammar, spelling, and source in correct format. SURPASSING 4 Concise, accurate, and complete—no major points of reading are missed and includes a non‐linguistic summary of main points. Student opinion of reading addresses the content and objectives of assignment, includes references to specific examples from the reading, and relates content to previous or current learning activities and raises new questions. Correct grammar, spelling, source in correct format, and uses citations.