Genes and Environment

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  • Created by: Mima
  • Created on: 23-02-14 19:58

Nature and Nurture

  • Genotype = genetic makeup
  • Phenotype = physical characteristics
    • Can be altered by genotype and environmental factors
  • Some phenotypes can be altered by environment e.g. blood group
    • when controlled at a SINGLE LOCUS they show discontinuous variation
    • fall into discrete groups with no overlap
  • Some affected by genotype and environmental factors e.g. human height
    • normal distribution curve (bell)
    • controlled at SEVERAL LOCI - polygenic inheritance
    • environment directly influences expression of the genes
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Polygenic Inheritance

  • Involves interaction of alleles at several loci
    • pattern of inheritance
    • polygenic
  • Environmental factors often multifactoral
  • e.g. eye colour
  • Greater number of loci = greater number of possibilities
  • If homozygous, alleles are the same
    • e.g. BB BB BB or bb bb bb
  • A punnet square shows possible outcomes of maternal and paternal gametes
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Genes and environment interactions p1

  • e.g. hair colour; height; MAOA; cancer
    • people are getting taller
    • more able to reach potential height 
      • better diet
      • less disease
      • better heating
    • shown that taller people have more children
    • dark pigment in skin/hair
    • form in melanocutes in root follicle and skin cells
    • activated by MSH - melanocyte stimulating hormone
    • receptors on curface of melanocyte cells
    • places melanin into melanosomes
    • collect around nucleus to protect from UV light
    • Some animals produce mutant tyrosinase - results in unstable form
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Genes and environment interactions p2

  • MAOA
    • Monoamine oxidase A - is an enzyme that catalyses breakdown of a neurotransmitter in the brain
    • (responsible for behaviour to stress)
    • Rare mutation produces no enzyme, results in more aggressive behaviour
    • Kings College (london) study shows childhood maltreatment also responsible, not just MAOA production
    • When cell production rate is faster than the rate of destruction
    • caused by damage to DNA
    • easily damaged by physical factors and carcinogens -carcinogens found in environment and by cell metabolism
    • mutations can occur when cells divide
      • cells go through G1, S, D2, M -- controlled progressions
      • proteins stimulate the next stage --cancer cells do not respond
    • Oncogenes code for next transition - can cause excessive cell division
    • Tumour Suppressor Genes stop the cycle - loss causes excessive cell division
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