Human Skin Color Evolution and Adaptation
33 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What determines the skin color primarily in humans?

Melanin

What are the two types of melanin responsible for variations in pigmentation?

  • Iridophores and Xanthophores
  • Melanocytes and Pheomelanin
  • Eumelanin and Xanthophores
  • Eumelanin and Pheomelanin (correct)

    • What does the article focus on regarding human evolution and environmental adaptation?

    Skin colour

    Which type of melanin gives the skin a black or dark brown color?

    <p>Eumelanin</p> Signup and view all the answers

    Excessive UVA exposure can lead to free radical oxidation of folate.

    <p>True</p> Signup and view all the answers

    What is the primary enzyme responsible for the synthesis of melanin?

    <p>Tyrosinase</p> Signup and view all the answers

    Match the following types of melanin with their colors:

    <p>Eumelanin = Black or dark brown Pheomelanin = Yellow-reddish</p> Signup and view all the answers

    What does the SNP rs1805007 represent in the gene MC1R?

    <p>Missense (Arg151Cys)</p> Signup and view all the answers

    What is the region of the SNP rs1426654 in the SLC24A5 gene?

    <p>AFR</p> Signup and view all the answers

    Exposure to UV radiation can decrease melanin production.

    <p>False</p> Signup and view all the answers

    What is the type of mutation for the SNP rs10756819 in the BNC2 gene?

    <p>Intron</p> Signup and view all the answers

    Which gene influences pigmentation primarily in African populations according to the text?

    <p>MFSD12</p> Signup and view all the answers

    Match the following genes with their respective SNPs:

    <p>HERC2/OCA2 = rs12913832 KITLG = rs642742 ASIP = rs4911414 IRF4/EXOC2 = rs1540771</p> Signup and view all the answers

    ______he _ allele of rs7948623 is associated with darker skin pigmentation.

    <p>T</p> Signup and view all the answers

    What is the ancestral allele in PDPK1 related to melanin production?

    <p>rs77665059-C</p> Signup and view all the answers

    In which regions do the two San populations have higher frequencies of the ancestral allele rs77665059-C compared to other African populations?

    <p>Southern Africa</p> Signup and view all the answers

    The UV levels in the Tibetan Plateau region are low.

    <p>False</p> Signup and view all the answers

    Match the following genes with their roles in the evolution of skin color in East Asians:

    <p>OCA2 = Influences pigmenta- tion across different species KITLG = Played a key role in skin colour evolution SLC24A2 = Associated with the development of fair skin PAH = Important component of the Cl- ion channel in melanin production</p> Signup and view all the answers

    What is the function of SLC24A5 in the mouse eye?

    <p>Slc24a5 protein plays an important role in the neuroepithelial pigment cells of the mouse eye.</p> Signup and view all the answers

    Which gene is responsible for delayed and reduced pigmentation of zebrafish skin melanophores?

    <p>SLC24A2</p> Signup and view all the answers

    Mutations in MITF contribute to phenotypic diversity in pigmentation among various species.

    <p>True</p> Signup and view all the answers

    SLC24A2 belongs to the __________ antiporter superfamily.

    <p>calcium/cation</p> Signup and view all the answers

    Match the following genes with their functions:

    <p>SLC24A5 = Controls skin lightening in European populations MITF = Regulates transcription of major pigmentation enzymes and is an oncogene</p> Signup and view all the answers

    Which genetic tool was used by Bajpai et al. in 2023 to identify regulators of melanogenesis?

    <p>CRISPR-Cas9</p> Signup and view all the answers

    In which region does the Arctic Fox (Vulpes lagopus) adapt to environmental changes by changing the color of its coat?

    <p>Arctic</p> Signup and view all the answers

    What is the role of TYR in the melanin biosynthesis pathway?

    <p>Catalyzes the oxidation of tyrosine to produce melanin</p> Signup and view all the answers

    The A allele at rs1042602 has a high frequency in European populations compared to African and Asian populations.

    <p>True</p> Signup and view all the answers

    Which gene is responsible for stabilizing the tyrosinase protein and enhancing its activity? Dopachrome Tautomerase (DCT) belongs to the ______ gene family.

    <p>Tyrosinase</p> Signup and view all the answers

    What enzyme located in the peroxisome may act synergistically with other hyperpigmentation genes to increase melanogenesis and tanning ability in humans?

    <p>GNPAT</p> Signup and view all the answers

    Which adaptive alleles reduced the enhancer activity of KITLG affecting melanocyte?

    <p>rs428316 (T allele)</p> Signup and view all the answers

    The adaptive alleles rs428316 and rs642742 increased the tanning ability of Tibetan population under UV exposure conditions.

    <p>True</p> Signup and view all the answers

    The gene ______ encodes a protein belonging to the potassium-dependent sodium-calcium exchanger family.

    <p>SLC24A5</p> Signup and view all the answers

    Match the following genes with their primary roles in shaping skin pigmentation: SLC24A5, SLC45A2, TYR, ASIP, MC1R.

    <p>SLC24A5 = Regulates human epidermal melanin production SLC45A2 = Associated with melanin synthesis TYR = Plays a pivotal role in melanin synthesis ASIP = Competitively antagonizes α-MSH MC1R = Associated with body pigment variations</p> Signup and view all the answers

    Study Notes

    Skin Colour Evolution and Adaptation

    • Human skin colour exhibits tremendous diversity across different geographical regions, influenced by environmental adaptations during human migrations.
    • Skin colour is a critical and externally visible component of human phenotype, regulated by genetic interactions and environmental factors.
    • The evolution of skin colour has been shaped by many genes and their interactions, as well as environmental factors combined with human migrations.

    The Role of Ultraviolet Radiation (UVR)

    • UVR, particularly UVB, promotes vitamin D synthesis in the body, an essential nutrient for calcium and phosphorus absorption and bone synthesis.
    • Low UVR and reduced vitamin D synthesis can lead to rickets (flawed bone development) and osteomalacia (soft bone disease) in adults.
    • Excessive UVR, primarily UVA, can lead to free radical oxidation of folate, resulting in its degradation. Folate is a crucial vitamin for human fertility.

    Melanin and Skin Colour

    • The balance between vitamin D and folate has driven the evolution of skin colour throughout human migrations.
    • Melanin is a potent antioxidant and free-radical scavenger, playing a crucial role in preventing DNA damage and tumourigenesis.
    • Eumelanin and pheomelanin are the two primary types of melanin, produced by melanocytes in the epidermis, responsible for variations in pigmentation, including skin and hair colour.

    Genetic Basis and Adaptive Evolution of Skin Colour in African Populations

    • The African continent exhibits high levels of UVR, climate, and environmental diversity, leading to variations in skin pigmentation across populations.

    • Darker skin reduces the risk of DNA damage caused by UVR and the degradation of folate, offering protection against skin cancer.

    • Genetic research has identified variants in or near genes strongly associated with skin pigmentation, including MFSD12, SLC24A5, PDPK1, HERC2/OCA2, MITF, and DDB1/CYB561A3/TMEM138 genes.### Melanin and Skin Pigmentation

    • Melanin is responsible for a range of colors from black to brown to yellow in bird feathers and skin tissues.

    • Its varied distribution determines the tinting, mottling, and reflective effects of feathers, influencing the appearance of bird features.

    • Carotenoids, which come from the food birds eat, are responsible for giving feathers their distinctive red, yellow, and orange colors.

    Melanosomes and Lysosomes

    • Melanin is produced in melanosomes and is highly expressed in skin tissues.
    • The reduction of Mfsd12 mRNA in the mouse can lead to an increase in eumelanin content, which occurs in a cell-autonomous manner.

    Genetic Associations with Skin Pigmentation

    • Comparative cross-species studies of humans, fish, and birds show that pigmentation can change significantly and adaptively based on ecological and social needs.
    • Two SNPs, rs56203814 and rs10424065, are associated with skin pigmentation phenotypes in African populations within the MFSD12 gene.
    • The ancestral allele T for both variants is exclusively found in African populations and exhibits a significant association with darker skin pigmentation.
    • Two upstream SNPs, rs6510760 and rs112332856, on MFSD12 also contribute to darker skin in Africans.

    Population-Specific Variants

    • Table 1 lists variants associated with skin pigmentation in African, East Asian, and European populations.
    • Interestingly, the frequencies of these variants differ significantly between populations.
    • For example, the rs56203814 variant is found in 20.8% of Africans, but is absent in East Asians and Europeans.

    Other Genes Associated with Skin Pigmentation

    • Other genes associated with skin pigmentation include DDB1, HERC2, OCA2, SLC24A5, and KITLG.
    • These genes are involved in various biological processes, including melanosome biogenesis, pigmentation, and skin development.
    • Variants in these genes have been found to be associated with skin pigmentation phenotypes in different populations.### Skin Pigmentation and UV Exposure
    • Exposure to UV radiation increases melanin production as a protective response to reduce DNA damage.
    • The DNA repair mechanism involving DDB1 (DNA damage-binding protein 1) affects melanocyte functionality and melanin synthesis.

    Genes Associated with Skin Pigmentation

    • TYR (Tyrosinase) gene: mutations in this gene are associated with skin pigmentation in different populations (e.g. rs1042602, rs1126809, rs1393350).
    • TYRP1 (Tyrosinase-related protein 1) gene: rs2733831 is associated with skin pigmentation in European populations.
    • UGT1A (UDP-glucuronosyltransferase 1A) gene: rs6742078 is associated with skin pigmentation in European populations.
    • DDB1 (DNA damage-binding protein 1) gene: plays a specific role in the adaptive response to high environmental pressure from UV exposure in African populations.
    • TMEM138 (transmembrane protein 138) gene: located near the DDB1 gene and is associated with skin pigmentation variation.

    Population Genetics and Skin Pigmentation

    • Multidirectional gene flow in Africa has had a profound effect on the genetic makeup of African populations and subsequent skin pigmentation.
    • The SLC24A5 gene is associated with lighter skin pigmentation in European populations and has been introduced into African populations through gene flow.
    • The rs1426654 A allele in the SLC24A5 gene is associated with lighter skin pigmentation in African populations and is nearly fixed in European populations.

    East Asian Populations

    • East Asian populations have relatively low levels of UV radiation, which reduces the need for protective melanin, resulting in an adaptive lighter skin.
    • OCA2 (Oculocutaneous albinism type 2) gene: encodes a P-protein, which is a unique 12-transmembrane transporter protein in the melanosome membrane.
    • rs1800414 (His615Arg) in the OCA2 gene: is associated with lighter skin pigmentation in East Asian populations and is nearly absent in European and African populations.
    • Positive selection for rs1800414-G in East Asia is thought to date back to the Late Palaeolithic period (25-30 kya).

    Pigmentation Genes Across Species

    • The fundamental vertebrate pathway for melanosome production is conserved across species.
    • OCA2 encodes the p-protein, which is an essential component of specific Cl- ion channels in melanosome membranes.
    • OCA2 affects eye and hair color in mice, and is involved in the regulation of melanin carrier differentiation in zebrafish.
    • OCA2 also has a significant effect on dorsoventral color patterns and feather coloration in birds.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Description

    Explore how human skin color has evolved and adapted to different environments. Learn about the process of human migration and its impact on skin color.

    More Like This

    Journey Through Human Evolution
    9 questions

    Journey Through Human Evolution

    Quizgecko avatar
    Quizgecko
    Human Evolution and Knowledge Transmission Quiz
    5 questions

    Human Evolution and Knowledge Transmission Quiz

    CarefreeCliff avatar
    CarefreeCliff
    Effect of Sunlight on Human Skin
    10 questions

    Effect of Sunlight on Human Skin

    OverjoyedSupernova avatar
    OverjoyedSupernova
    Human Biocultural Evolution Quiz
    8 questions

    Human Biocultural Evolution Quiz

    InterestingCarnelian518 avatar
    InterestingCarnelian518
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser