DOCSLIB.ORG

Worldwide Polymorphism at the MC1R Locus and Normal Pigmentation Variation in Humans

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Worldwide Polymorphism at the MC1R Locus and Normal Pigmentation Variation in Humans Peptides 26 (2005) 1901–1908 Review Worldwide polymorphism at the MC1R locus and normal pigmentation variation in humans Kateryna Makova a,∗, Heather Norton b a Department of Biology, The Pennsylvania State University, 518 Mueller Lab, University Park, PA 16802, USA b Department of Anthropology, The Pennsylvania State University, 409 Carpenter Building, University Park, PA 16802, USA Received 20 August 2004; accepted 16 December 2004 Available online 23 June 2005 Abstract While there have been many advances in our understanding of the genetics of pathological skin pigmentation in humans, our knowledge about what determines variation in normal skin color is still incomplete. Variation in one gene, melanocortin 1 receptor (MC1R), has been associated with red hair and fair skin in Europeans. However, this gene might also play an important role in shaping pigmentation of other human populations, where it experiences different selective pressures. Below we review what is currently known about polymorphism and selection at the MC1R coding and promoter regions in human populations, the pattern of MC1R evolution in nonhuman primates, and the interaction of MC1R with other genes. © 2005 Elsevier Inc. All rights reserved. Keywords: MC1R; Pigmentation; Natural selection; Human evolution Contents 1. Introduction .................................................................................................... 1901 2. Polymorphism of MC1R in human populations: coding region ....................................................... 1902 2.1. European populations...................................................................................... 1902 2.2. Asian populations ......................................................................................... 1903 2.3. African populations ....................................................................................... 1904 3. Polymorphism of MC1R in human populations: promoter ........................................................... 1904 4. MC1R evolution in primates ...................................................................................... 1905 5. Interactions between MC1R and other genes in human populations ................................................... 1905 6. Future directions ................................................................................................ 1906 Acknowledgements.............................................................................................. 1907 References ..................................................................................................... 1907 1. Introduction This variation has long intrigued geneticists and anthro- pologists, especially because it is believed to have been Human skin and hair pigmentation are complex traits shaped, at least in part, by the action of natural selection that show variation both within and between populations. (e.g. [7,22,24,33,55]). While genes responsible for pigmenta- tion disorders such as albinism have been known for nearly a decade (for a review, see [20]), it is only recently that we have ∗ Corresponding author. Tel.: +1 814 863 1619; fax: +1 814 865 9131. developed a better understanding of the genetic basis under- E-mail address: [email protected] (K. Makova). lying normal variation in human skin and hair pigmentation. 0196-9781/$ – see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.peptides.2004.12.032 1902 K. Makova, H. Norton / Peptides 26 (2005) 1901–1908 The major breakthrough in this area was due to the discovery MC1R isoform is a 317-amino acid 7 pass transmembrane of mutations in the melanocortin 1 receptor (MC1R) gene that protein. Mutagenesis studies of other MCRs suggest that the are associated with normal variation in skin color [53]. The transmembrane domains TM1, TM2, TM3, TM6, and TM7 MC1R is a cell-surface receptor of melanocytes and a major are likely to contain the MC1R’s primary hormone-binding player in the melanin production pathway. The MC1R gene sites [39–41]. Robbins et al. [38] identified two gain-of- has been observed to regulate the switch between the pro- function point mutations in this region in the mouse, and duction of eumelanin (brown/black pigment) and pheome- human MC1R polymorphisms associated with red hair and lanin. Eumelanin together with pheomelanin (red/yellow fair skin have been observed here as well (e.g. [35,53]). pigment) constitute the two main pigments of the skin Like other G protein-coupled receptors, MC1R signal trans- and hair. duction is mediated via the GTP-binding protein to acti- The melanocortin 1 receptor belongs to a family of vate adenylyl cyclase and increase levels of cellular cAMP. G protein-coupled receptors known as the melanocortin Intracellular loops of G protein-coupled receptors are nec- receptors (MCRs). In mammals, the MC1R responds to ␣- essary for protein interactions with GTP-binding proteins, melanocyte-stimulating hormone (␣-MSH) and adrenocor- suggesting that these may be key functional regions of the ticotropic hormone (ACTH), both products of proopiome- MC1R. Mutations having an effect on pigmentation pheno- lanocortin (POMC). When the MC1R is activated by ␣-MSH, type have in fact been found in the second intracellular loop intracellular cAMP levels are increased via activation of [13]. adenylyl cyclase, leading to the production of elevated levels In the mouse, loss of function mutations at exten- of tyrosinase and ultimately to the production of brown/black sion lead to a yellow coat phenotype due to the over- eumelanin (Fig. 1). However, the antagonistic agouti signal- production of pheomelanin relative to eumelanin, while ing protein (ASIP) can compete with ␣-MSH for binding gain of function mutations at extension are associated with to the MC1R. When ASIP is able to completely block or melanic morphs [38]. Extension is also responsible for eume- inhibit ␣-MSH, pheomelanin is produced instead of eume- lanin/pheomelanin production in other mammals, such as lanin (Fig. 1). horses, dogs, pigs and sheep, as well as in birds (e.g. The human MC1R gene, located at chromosome 16q24.3 [18,38,52]). [14], has an open reading frame of 951 bp and until recently The human MC1R gene has been shown to be highly was thought to be composed of a single exon. However, Tan polymorphic (e.g. [6,15,35,47,53]) with many variants being et al. [51] identified an alternative mRNA splice variant at associated with a red hair/fair skin phenotype. Mutations in the 3 end of the gene. This “long” MC1R isoform (MC1RB) MC1R have also been associated with poor tanning ability contains a second exon encoding 65 amino acids, although and an increased risk of skin cancers, possibly since pheome- the functional significance of this alternative form is currently lanin can produce free radicals in the presence of ultraviolet unknown. radiation (UVR) and thus have deleterious effects on the The MC1R gene maps to the murine extension locus melanocytes [23,32]. and is expressed in a number of cell types, most notably There are a number of excellent reviews that focus on the melanocytes. The protein encoded by the “short” human relationship between the MC1R genotype and the red hair phenotype (e.g. [36,37,50]). In contrast, this review will focus on MC1R polymorphism across the entire human species (rather than limiting our discussion to variation in European populations), the role of selection in shaping MC1R diver- sity, and MC1R polymorphism and evolution in non-human primates. 2. Polymorphism of MC1R in human populations: coding region 2.1. European populations Early reports indicated an association between the MC1R variants and a red hair/light skin phenotype. By screening 30 red-haired individuals, Valverde et al. [53] identified nine different changes in the MC1R coding region, all leading to amino acid substitutions. Frequently, there were two amino Fig. 1. Diagram of the alternate effects of the binding of ␣-MSH or ASIP to the melanocortin 1 receptor. Binding of ␣-MSH leads to the production of acid mutations within the same allele. Eight of these substitu- brown/black eumelanin, while binding of the antagonistic ligand ASIP leads tions span the second transmembrane domain of the MC1R. to the production of red/yellow pheomelanin. Another study investigated twins with red hair and identified K. Makova, H. Norton / Peptides 26 (2005) 1901–1908 1903 11 additional amino acid variants at the MC1R [6]. Three at most other genomic regions investigated in non-Africans substitutions were significantly associated with red hair. [34]. Note that this variation is mostly nonsynonymous. Interestingly, in several cases, dizygotic twins possessing Two alternative theories were proposed to explain the identical MC1R alleles had discordant hair color, suggesting high level of MC1R polymorphism in Europeans. First, Rana that the MC1R gene cannot be solely responsible for the red et al. [35] suggested that this might support the vitamin D hair phenotype [6]. A more detailed study was later conducted hypothesis [9,22]. Vitamin D is produced by photoconver- in Irish populations [47], again providing evidence of signif- sion of 7-dehydrocholesterol in skin capillaries. In regions icant association of MC1R variants with red hair. Currently of low sunlight, light skin can be advantageous, as it allows more than 30 variant alleles have been reported for European more ultraviolet radiation to penetrate through the skin pre- populations with nine variants being at high frequency (each venting vitamin D deficiency and
Load more

Recommended publications
  • Beware, Red Heads Don't Numb!
    Research Article Published: 08 Mar, 2019 Journal of Ophthalmology Forecast Beware, Red Heads Don’t Numb! Matthews JM*, Petrykowski B and Davidorf F Havener Eye Institute, The Ohio State University Wexner Medical Center, USA Abstract Background: The use of topical anesthesia in the outpatient setting by Ophthalmologists has seen a dramatic increase since the development of antivegf medications. Each year, there are an estimated 6-7 million anti-vegf injections performed in the United States. People with red hair have a mutation of the MC1R gene, which has been associated with decreased effectiveness of local anesthesia. The purpose of this communication is to alert the ophthalmology community of potential for inadequate anesthesia for intraocular injections Methods: IRB was obtained through OSU IRB. 175 patients receiving intravitreal injections were randomly surveyed to determine incidence of poor analgesia with injections. Results: Overall, 19/175 patients were found to have decreased effectiveness of local anesthesia. We found a surprisingly high incidence (10.5%) of patients who require increased amounts of local anesthesia than is commonly used in those with natural red/auburn hair. Conclusion: We encourage ophthalmologists who use local anesthesia for their patients to include an assessment of their response to dental anesthesia. These individuals need to be identified who have had previously bad experiences with poor responses to local anesthesia. We recommend using twice the amount of topical anesthesia in these patients. Keywords: Intravitreal injections; MC1R Gene; Red hair; VEGF; Topical anesthesia Introduction The use of topical anesthesia in the outpatient setting by Ophthalmologists has seen a dramatic increase since the development of antivegf medications.
    [Show full text]
  • What Does It Mean to Be a Redhead in Literature?
    The University of Southern Mississippi The Aquila Digital Community Honors Theses Honors College Spring 5-2015 The Importance of Appearances in Literature: What Does It Mean to Be a Redhead in Literature? Chelsea J. Anderson University of Southern Mississippi Follow this and additional works at: https://aquila.usm.edu/honors_theses Part of the Children's and Young Adult Literature Commons Recommended Citation Anderson, Chelsea J., "The Importance of Appearances in Literature: What Does It Mean to Be a Redhead in Literature?" (2015). Honors Theses. 274. https://aquila.usm.edu/honors_theses/274 This Honors College Thesis is brought to you for free and open access by the Honors College at The Aquila Digital Community. It has been accepted for inclusion in Honors Theses by an authorized administrator of The Aquila Digital Community. For more information, please contact [email protected]. The University of Southern Mississippi The Importance of Appearances in Literature: What Does It Mean to Be a Redhead in Literature? by Chelsea Anderson A Thesis Submitted to the Honors College of The University of Southern Mississippi in Partial Fulfillment of the Requirement for the Degree of Bachelor of Arts in the Department of English May 2015 ii Approved by ____________________________________ Alexandra Valint, Ph. D., Thesis Adviser Assistant Professor of English ____________________________________ Eric Tribunella, Ph. D., Chair Department of English ____________________________________ Ellen Weinauer, Ph.D., Dean Honors College iii Abstract In literature, appearances always seem to play a major part of each character. The physical descriptions of each character are important to the development of the story. Therefore, it seems that a character’s physical appearance becomes an important part of character development, and his/her physical traits help to determine the type of character he/she will be.
    [Show full text]
  • Genetics of Hair and Skin Color
    11 Sep 2003 14:51 AR AR201-GE37-04.tex AR201-GE37-04.sgm LaTeX2e(2002/01/18) P1: GCE 10.1146/annurev.genet.37.110801.143233 Annu. Rev. Genet. 2003. 37:67–90 doi: 10.1146/annurev.genet.37.110801.143233 Copyright c 2003 by Annual Reviews. All rights reserved First published online as a Review in Advance on June 17, 2003 GENETICS OF HAIR AND SKIN COLOR Jonathan L. Rees Systems Group, Dermatology, University of Edinburgh, Lauriston Buildings, Lauriston Place, Edinburgh, EH3 9YW, United Kingdom; email: [email protected] Key Words melanin, melanocortin 1 receptor (MC1R), eumelanin, pheomelanin, red hair ■ Abstract Differences in skin and hair color are principally genetically deter- mined and are due to variation in the amount, type, and packaging of melanin polymers produced by melanocytes secreted into keratinocytes. Pigmentary phenotype is genet- ically complex and at a physiological level complicated. Genes determining a number of rare Mendelian disorders of pigmentation such as albinism have been identified, but only one gene, the melanocortin 1 receptor (MCR1), has so far been identified to explain variation in the normal population such as that leading to red hair, freckling, and sun-sensitivity. Genotype-phenotype relations of the MC1R are reviewed, as well as methods to improve the phenotypic assessment of human pigmentary status. It is argued that given advances in model systems, increases in technical facility, and the lower cost of genotype assessment, the lack of standardized phenotype assessment is now a major limit on advance. CONTENTS INTRODUCTION ..................................................... 68 BIOLOGY OF HUMAN PIGMENTATION ................................ 69 by San Jose State University on 10/05/10.
    [Show full text]
  • The True Roots and Origin of the Scots
    THE TRUE ROOTS AND ORIGIN OF THE SCOTS A RESEARCH SUMMARY AND POINTERS TOWARD FURTHER RESEARCH “Wherever the pilgrim turns his feet, he finds Scotsmen in the forefront of civilization and letters. They are the premiers in every colony, professors in every university, teachers, editors, lawyers, engineers and merchants – everything, and always at the front.” – English writer Sir Walter Besant Copyright © C White 2003 Version 2.1 This is the first in a series of discussion papers and notes on the identity of each of the tribes of Israel today Some Notes on the True Roots and Origin of the Scots TABLE OF CONTENTS Introductory Remarks 3 Ancient Judah 6 Migrations of Judah 17 British Royal Throne 25 National and Tribal Emblems 39 Scottish Character and Attributes 44 Future of the Scots – Judah’s Union with the rest of Israel 55 Concluding Remarks 62 Bibliography 65 “The mystery of Keltic thought has been the despair of generations of philosophers and aesthetes … He who approaches it must, I feel, not alone be of the ancient stock … but he must also have heard since childhood the deep and repeated call of ancestral voices urging him to the task of the exploration of the mysteries of his people … He is like a man with a chest of treasure who has lost the key” (The Mysteries of Britain by L Spence) 2 Some Notes on the True Roots and Origin of the Scots INTRODUCTORY REMARKS Who really are the Scottish peoples? What is their origin? Do tradition, national characteristics and emblems assist? Why are they such great leaders, administrators and inventors? Is there a connection between them and the ancient Biblical tribe of Judah? Why did the British Empire succeed when other Empires did not? Was it a blessing in fulfillment of prophecies such as that in Gen 12:3? Why were the Scots so influential in the Empire, way beyond their population numbers? Today book after book; article after article; universities, politicians, social workers spread lies about the British Empire, denigrating it.
    [Show full text]
  • The Genetics of Human Skin and Hair Pigmentation
    GG20CH03_Pavan ARjats.cls July 31, 2019 17:4 Annual Review of Genomics and Human Genetics The Genetics of Human Skin and Hair Pigmentation William J. Pavan1 and Richard A. Sturm2 1Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892, USA; email: [email protected] 2Dermatology Research Centre, The University of Queensland Diamantina Institute, The University of Queensland, Brisbane, Queensland 4102, Australia; email: [email protected] Annu. Rev. Genom. Hum. Genet. 2019. 20:41–72 Keywords First published as a Review in Advance on melanocyte, melanogenesis, melanin pigmentation, skin color, hair color, May 17, 2019 genome-wide association study, GWAS The Annual Review of Genomics and Human Genetics is online at genom.annualreviews.org Abstract https://doi.org/10.1146/annurev-genom-083118- Human skin and hair color are visible traits that can vary dramatically Access provided by University of Washington on 09/02/19. For personal use only. 015230 within and across ethnic populations. The genetic makeup of these traits— Annu. Rev. Genom. Hum. Genet. 2019.20:41-72. Downloaded from www.annualreviews.org Copyright © 2019 by Annual Reviews. including polymorphisms in the enzymes and signaling proteins involved in All rights reserved melanogenesis, and the vital role of ion transport mechanisms operating dur- ing the maturation and distribution of the melanosome—has provided new insights into the regulation of pigmentation. A large number of novel loci involved in the process have been recently discovered through four large- scale genome-wide association studies in Europeans, two large genetic stud- ies of skin color in Africans, one study in Latin Americans, and functional testing in animal models.
    [Show full text]
  • Investigating DNA Methylation As a Potential Mediator Between Pigmentation Genes, Pigmentary Traits and Skin Cancer
    Genetics of DNA Methylation Consortium (2020). Investigating DNA methylation as a potential mediator between pigmentation genes, pigmentary traits and skin cancer. Pigment Cell & Melanoma Research. https://doi.org/10.1111/pcmr.12948 Publisher's PDF, also known as Version of record License (if available): CC BY Link to published version (if available): 10.1111/pcmr.12948 Link to publication record in Explore Bristol Research PDF-document This is the final published version of the article (version of record). It first appeared online via Wliey at https://doi.org/10.1111/pcmr.12948 . Please refer to any applicable terms of use of the publisher. University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/ Received: 28 May 2020 | Revised: 16 October 2020 | Accepted: 17 November 2020 DOI: 10.1111/pcmr.12948 ORIGINAL ARTICLE Investigating DNA methylation as a potential mediator between pigmentation genes, pigmentary traits and skin cancer Carolina Bonilla1,2 | Bernardo Bertoni3 | Josine L. Min2,4 | Gibran Hemani2,4 | Genetics of DNA Methylation Consortium | Hannah R. Elliott2,4 1Departamento de Medicina Preventiva, Faculdade de Medicina, Universidade de São Abstract Paulo, São Paulo, Brazil Pigmentation characteristics are well-known risk factors for skin cancer. 2 Population Health Sciences, Bristol Medical Polymorphisms in pigmentation genes have been associated with these traits and School, University of Bristol, Bristol, UK 3Departamento de Genética, Facultad de with the risk of malignancy.
    [Show full text]
  • Celticism: Between Race and Nation
    Celticism: Between Race and Nation CHRIS MORASH 'What', asked Douglas Hyde in 'The Necessity for De-Anglicising Ireland' (1892), 'lies at the back of the sentiments of nationality with which the Irish millions seem so strongly leavened?'The answer, he declares, is racial memory; I believe that what is largely behind it is the half unconscious feeling that the race which at one time held possession of more than half Europe ... is now - almost extirpated and absorbed elsewhere - making its last stand for independence in this island of Ireland; and do what they may the race of today cannot wholly divest itself from the mantle of its own past.' A passage like this forces us to interrogate the relationship between nation- alism and racialism on this island. This is, after all, the man who became the first President of Ireland, a moderate when compared, for instance, with Arthur Griffith, Vice-President of Sinn F&m in the first DO, who wrote in 1913 that no Irishman needed an excuse for 'declining to hold the negro his peer in right' 2 To raise the issue of race in such a context is to ask awkward questions, liable to expose the person who asks them to charges of being a revisionist heretic of the worst kind. When they have been raised (and it has not been often), it has usually been with the proviso that, as Luke Gibbons puts it in his essay 'Race against Time: Racial Discourse and Irish History', 'not all the con- cepts of Irishness which emerged under the aegis of cultural nationalism were dependent on racial modes of identity',3 although he admits that those which Douglas Hyde, 'The Necessity for De-Anglicising Ireland', in The Field Day Anthology of Irish Writing, vol.
    [Show full text]
  • Human Pigmentation Variation: Evolution, Genetic Basis, and Implications for Public Health
    YEARBOOK OF PHYSICAL ANTHROPOLOGY 50:85–105 (2007) Human Pigmentation Variation: Evolution, Genetic Basis, and Implications for Public Health Esteban J. Parra* Department of Anthropology, University of Toronto at Mississauga, Mississauga, ON, Canada L5L 1C6 KEY WORDS pigmentation; evolutionary factors; genes; public health ABSTRACT Pigmentation, which is primarily deter- tic interpretations of human variation can be. It is erro- mined by the amount, the type, and the distribution of neous to extrapolate the patterns of variation observed melanin, shows a remarkable diversity in human popu- in superficial traits such as pigmentation to the rest of lations, and in this sense, it is an atypical trait. Numer- the genome. It is similarly misleading to suggest, based ous genetic studies have indicated that the average pro- on the ‘‘average’’ genomic picture, that variation among portion of genetic variation due to differences among human populations is irrelevant. The study of the genes major continental groups is just 10–15% of the total underlying human pigmentation diversity brings to the genetic variation. In contrast, skin pigmentation shows forefront the mosaic nature of human genetic variation: large differences among continental populations. The our genome is composed of a myriad of segments with reasons for this discrepancy can be traced back primarily different patterns of variation and evolutionary histories. to the strong influence of natural selection, which has 2) Pigmentation can be very useful to understand the shaped the distribution of pigmentation according to a genetic architecture of complex traits. The pigmentation latitudinal gradient. Research during the last 5 years of unexposed areas of the skin (constitutive pigmenta- has substantially increased our understanding of the tion) is relatively unaffected by environmental influences genes involved in normal pigmentation variation in during an individual’s lifetime when compared with human populations.
    [Show full text]
  • The Impact of Red Hair Color on Perceived Attributes and Employment Outcomes for Caucasian Male and Female Job Applicants
    Watson, Griggs and Szeman When Hair Color Influences Job Marketability: The Impact of Red Hair Color on Perceived Attributes and Employment Outcomes for Caucasian Male and Female Job Applicants Bonnie F. Watson,* Dr. Tracy L. Griggs,§ and Michael Szeman⸸ Abstract This study explores how hair color affects perceptions of male and female Caucasian job applicants seeking professional managerial positions. Using a between-subjects design, 158 participants from two samples (Sample 1: future managers, Sample 2: current managers in the banking industry) were asked to rate one of six “paper” applicants after examining a hypothetical job description, a résumé, and a profile picture of the applicant. Paper applicants differed in terms of their gender (male or female) as well as their hair color, which was electronically manipulated (blonde, red, and brunette). Results from both samples reveal partial support for the hypotheses. In a sample of future managers, red-haired applicants were rated significantly lower than blondes and brunettes on all dependent variables including likelihood to hire, beginning salary, physical attractiveness and intelligence, but not on ability to handle stress or ability to supervise others. There were no gender differences for red-haired female and red-haired male job applicants. Findings from the banking industry sample reveal similar effects for likelihood to hire, such that red-haired applicants were rated lower than blondes and brunettes, although none of the other differences were significant. Results of this study
    [Show full text]
  • Ginger Masculinities
    University of Massachusetts Amherst ScholarWorks@UMass Amherst Masters Theses Dissertations and Theses November 2015 Ginger Masculinities Donica O'Malley University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/masters_theses_2 Part of the Communication Commons Recommended Citation O'Malley, Donica, "Ginger Masculinities" (2015). Masters Theses. 288. https://doi.org/10.7275/7462047 https://scholarworks.umass.edu/masters_theses_2/288 This Campus-Only Access for Five (5) Years is brought to you for free and open access by the Dissertations and Theses at ScholarWorks@UMass Amherst. It has been accepted for inclusion in Masters Theses by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. GINGER MASCULINITIES A Thesis Presented by DONICA O’MALLEY Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of MASTER OF ARTS September 2015 Communication © Copyright by Donica O’Malley 2015 All Rights Reserved GINGER MASCULINITIES A Thesis Presented by DONICA O’MALLEY Approved as to style and content by: _______________________________________ Leda Cooks, Chair _______________________________________ Claudio Moreira, Member ____________________________________ Erica Scharrer, Chair Department of Communication ABSTRACT GINGER MASCULINITIES SEPTEMBER 2015 DONICA O’MALLEY, B.A., UNIVERSITY OF MASSACHUSETTS AMHERST M.A., UNIVERSITY OF MASSACHUSETTS AMHERST
    [Show full text]
  • Iron Age Celts Lived in Britain and Ireland from 750BC Until 43AD
    Dear Pluto and Neptune, In school we have been learning about the Iron Age. This week you are going to learn about the Iron Age people called the Celts. Read this power point, with a grown up if you would like, and have a look at the tasks I have set you. Enjoy your time working from home! I’m looking forward to seeing you all soon. Don’t forget to keep your work safe so you can show us when we get back to school. Mrs Hope Who Were the Celts? The Iron Age Celts lived in Britain and Ireland from 750BC until 43AD. They came from all over Europe, from Austria and Switzerland to Southern France and Spain. The word Celt comes from the Greek word Keltoi although its definition is unclear. 750 BC means the Celts were in Britain 750 years before Jesus was born. Tribes Celts were part of tribes (different groups), and each tribe had their own king or queen. This meant there was a lot of fighting between neighbouring tribes. There were three main Celtic groups: The Gauls The Britons The Gaels Famous Queen Boudicca: Boudicca was queen of the Iceni tribe. She was described as tall with thick, red hair, and wore a bright tunic and a cape pinned with a brooch. She brandished her sword as she rode a chariot, and she hated the Romans. Iron Age Celts The Iron Age Celts are called this because they discovered iron and became great craftsmen who created weapons and household objects from this new metal.
    [Show full text]
  • MC1R Gene Melanocortin 1 Receptor
    MC1R gene melanocortin 1 receptor Normal Function The MC1R gene provides instructions for making a protein called the melanocortin 1 receptor. This receptor plays an important role in normal pigmentation. The receptor is primarily located on the surface of melanocytes, which are specialized cells that produce a pigment called melanin. Melanin is the substance that gives skin, hair, and eyes their color. Melanin is also found in the light-sensitive tissue at the back of the eye ( the retina), where it plays a role in normal vision. Melanocytes make two forms of melanin, eumelanin and pheomelanin. The relative amounts of these two pigments help determine the color of a person's hair and skin. People who produce mostly eumelanin tend to have brown or black hair and dark skin that tans easily. Eumelanin also protects skin from damage caused by ultraviolet (UV) radiation in sunlight. People who produce mostly pheomelanin tend to have red or blond hair, freckles, and light-colored skin that tans poorly. Because pheomelanin does not protect skin from UV radiation, people with more pheomelanin have an increased risk of skin damage caused by sun exposure. The melanocortin 1 receptor controls which type of melanin is produced by melanocytes. When the receptor is activated, it triggers a series of chemical reactions inside melanocytes that stimulate these cells to make eumelanin. If the receptor is not activated or is blocked, melanocytes make pheomelanin instead of eumelanin. Common variations (polymorphisms) in the MC1R gene are associated with normal differences in skin and hair color. Certain genetic variations are most common in people with red hair, fair skin, freckles, and an increased sensitivity to sun exposure.
    [Show full text]