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Dark Skin, Blond Hair

Surprise in the Solomon Islands



Co Authors:

Khadijah I. Makky
Department of Biomedical Sciences
Marquette University
khadijah.makky@marquette.edu

Audra A. Kramer
Department of Biomedical Sciences
Marquette University

Abstract:

This interrupted case is based on a genome wide association study (GWAS) that identified the genetic variation causing some inhabitants of the Solomon Islands to have blond hair. The case illustrates the connection between genotype and phenotype, and an application of Hardy-Weinberg equilibrium. The narrative focusses on John and his new roommate, Peter, from the Solomon Islands who happens to have dark skin and blond hair. Using thought-provoking questions students learn about the genetics and the biochemistry of the hair color trait and how a single genetic variation can influence phenotype. Is migration or mutation involved?  Upon completion of the activity students will know the source of the genetic variation that causes the blond hair phenomenon in the Solomon Islands and if it has any European origins. The case was written for an upper-level genetics course, but could also be adapted for introductory biology or for a genetics course for non-majors. An optional PowerPoint presentation with clicker questions is available for download from within the Answer Key.

Objectives:
  • Understand the connection between genotype and phenotype, and that single genetic mutation in a coding gene can affect the function of the protein product and have a significant effect on the resulting phenotype (trait).
  • Understand that genetic mutation is part of evolution and can lead to variation in human traits.
  • Avoid the misconception that mutations always lead to diseases.
  • Apply Hardy-Weinberg equilibrium to calculate allele frequencies and genotype frequencies.
  • Learn how allele frequencies can help us answer some genetic questions regarding human traits.
  • Examine the effect of population size on allele frequency and trait frequency.
Keywords: polygenic traits; genotype-phenotype; Hardy-Weinberg equilibrium; HWE; population genetics; blond hair trait, blonde; blond; dark skin; TYRP1; GWAS; Solomon Islands
Topical Area: N/A
Educational Level: Undergraduate lower division, Undergraduate upper division
Formats: PDF, PowerPoint
Type/Method: Clicker, Interrupted
Language: English
Subject Headings: Genetics / Heredity   Biology (General)  
Date Posted: 12/27/2016
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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My colleagues and I were initially quite interested in this case but we would like to point out, for anyone planning to use it, that the story and the solution are over-simplifying the reality of that system. There have been a few later papers that came out since the Science paper that highlight that these islands are very heterogeneous in terms of the presence of the allele focused on in this case (i.e. may not be appropriate to pool data), that there are likely multiple alleles involved in seeing blonde hair on islanders (depending on the island), that genetic drift has had a significant role to play, along with positive selection, and a high probability of a founder effect (as opposed to a within island population mutation arising). We feel that if students do any digging whatsoever - they will become confused by the answers provided in the case. Perhaps the authors need another section that highlights how scientific understanding evolves when more data and analyses are conducted to highlight how the explanation for their dilemma may be much more complex than initially thought.


Glenna Malcolm
Biology
Penn State University
University Park, PA
gmm193@psu.edu
1/26/2017
AUTHOR REPLY: Thank you for the comment. Genetically, this case is accurate, and based on the publication in 2012 the science is solid. That being said, science changes all the time. In addition, the determination of the cause of the blond hair in the Solomon Islands is not actually one of the main objectives of the case; rather, the story of the Solomon Islands is a tool to explain several genetic concepts including the Hardy Weinberg equilibrium. We understand that this case has a potentially wide range of audience. On one side of the spectrum we have high school teachers who want a simplified case to apply this genetic concept and on the other side of the spectrum we have teachers with probably advanced students such as this reader who thought that this case is simplifying the issue. For the latter group, teachers are encouraged to modify the case to suit the needs of their course.


Khadijah I. Makky
Department of Biomedical Sciences
Marquette University
Milwaukee, WI
khadijah.makky@marquette.edu
1/31/2017



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