Rusva barzda dažniausiai asocijuojasi su Airija ir jos gyventojais vyrais. Kodėl airių barzdos rusvos, nepaisant to, kokia jų plaukų spalva yra?
Kiekvienas pastebėjo, kad net jei airio plaukai yra šviesūs, rudi arba juodi, net jei jo giminėje per amžius nebuvo rusvaplaukių, barzdoje paprastai vis tiek „prasišviečia“ rusva sruogelė. Keista, bet iš tikrųjų gana dažnai, tiesą sakant, du iš penkių vyrų turi rusvas barzdas. Taigi, airiai nėra ypatingesni už kitus ir tai nepriklauso nuo jų keltiškos prigimties.
Olandijos nacionalinio genetikos ir paveldimų bruožų informacijos centro atstovas Petra Haak-Bloem aiškina tai gana techniškai. Jis sako, kad genai, lemiantys plaukų spalvą, yra „nepakankamai dominuojantys paveldimų bruožų spektre“. Tai reiškia, kad nėra vieno dominuojančio geno, viskas priklauso nuo genų tarpusavio sąveikos. Kiekvienas genas, veikdamas vienas kitą, atlieka savo vaidmenį ir todėl įvairių kūno sričių plaukų spalva skiriasi, tame tarpe ir barzdos.
Haak-Bloem sako: „Kalbant apibendrintai, žmonės paveldi plaukų spalvą ne tik iš tėvų, bet ir iš savo senelių bei ankstesnių protėvių. Taigi, visiškai įmanoma, kad vienas tolimas protėvis turėjo rusvą plaukų spalvą, kuri vėl „išlindo“ tam tikrų genų kombinacijų dėka – kas gali būti labai netikėta tėvams.“
Visame tame logika yra, bet kodėl būtent kai kurie vyrai turi rusvas barzdas? Gal tam turi poveikio aplinkos oras?
Ekspertas teigia: „Baltaodžiams žmonėms oro poveikis priklauso nuo dviejų rūšių melanino: eumelanino (juodojo pigmento) ir feomelanino (raudonojo pigmento). Tamsiaplaukių žmonių ląstelės turi tik eumelaniną, šviesiaplaukiai jo turi mažiau, o rusvaplaukiai daugiausia turi feomelanino.“
Daugiau nei prieš dešimtmetį, mokslininkai atrado, kad vienas 16 chromosomos genas (MC1R) vaidina svarbų vaidmenį, žmonėms paveldint rusvų plaukų spalvą. MC1R užduotis yra padaryti baltymą, vadinamą melanocortin 1, kuris atlieka svarbų vaidmenį, paverčiant feomelaniną į eumelaniną. Haak-Bloem teigia, kad kai kas nors paveldi dvi mutavusio geno MC1R versijas (po vieną iš motinos ir tėvo), mažesnis feomelanino kiekis paverčiamas eumelaninu. Feomelaninas kaupiasi pigmentinėse ląstelėse ir asmuo paveldi rusvus plaukus bei šviesią odą.
Kaip jums tai? Iš esmės, dauguma vyrų turi savo genetikoje „įbarstytus“ rusvų plaukų genus, net jei tai nebuvo tėvų ar senelių bruožas. Taigi, rusva barzda didžiuojasi daug daugiau vyrų, nei airiams ir Airijoje gyvenantiems ne airiams atrodo.
Kaip atsirado rusvų plaukų genas?
Mokslininkai tiki, kad „rusvas“ genas arba „V6OL alelis“ išsivystė prieš 50000 metų, kai žmonės persikėlė iš Afrikos į Europą. Šis genas padarė žmogaus odą šviesesne, nes jie buvo veikiami saulės ir gaudavo mažesnį vitamino D kiekį. Atradimas buvo padarytas, išstudijavus 1000 Ispanijos žmonių genų evoliuciją.
Dešimt procentų Airijos žmonių turi rusvus plaukus. Jungtinėje Karalystėje ir Airijoje iš viso yra apie 20 milijonų žmonių, kurių genai gali įtakoti rusvų plaukų paveldimumą. Šis genas yra dominuojantis tarp šiaurės europiečių.
Iš kitos pusės šviesesnė oda gali įtakoti kai kurių ligų atsiradimą, pavyzdžiui, melanomos – sunkios vėžio formos, bet to priežastimi nebūtinai gali būti „rusvasis“ genas. Taip pat nustatyta, kad melanoma negali turėti arba turi labai menką poveikį individo genetikai bei ateinančioms kartoms.
Škotijoje 2012 metais atliktas tyrimas rodo, kad niūkus klimatas išprovokavo genetinę adaptaciją. Iš esmės tai reiškia, kad rusvi plaukai padeda pilnai išnaudoti saulėtas dienas ir suteikia galimybę organizmui įsisavinti daugiau vitamino D.
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