B1 Variation and Inheritance mindmap

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  • Created by: Spanish
  • Created on: 30-04-16 14:11
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  • Variation and interheritance
    • Inherited Characteritics
      • Some human characteristic,such as facial features, can be inherited. They can be dominant or recessive
      • Alleles are different versions of the same gene
      • There is a debate over how much 'nature or nurture' (genetic or environmental factors) affect intelligence, sporting ability or health
      • Dominant and recessive characteristics depend on dominant and recessive alleles
        • Dominant alleles are expressed when present but recessive alleles are expressed only in the absence of the dominant allele
    • Chromosomes
      • Most body cells have the same number of chromosomes. The number depends on the species of organism.
        • Human cells have 23 pairs
          • Sex chromosomes determine sex in mammals. Females have identical sex chromosomes called XX, males have different sex chromosomes called XY
            • A sperm will carry either an X or a Y chromosome. All eggs will carry an X chromosome
              • There is a random chance of which sperm fertilises an egg. There is therefore an equal chance of the offspring being male or female
    • Genetic variation
    • A monohybrid cross
      • A monohybrid cross involves only one pair of characteristics controlled by a single gene, one allele being dominant and one recessive
      • Homozygous means having identical alleles, being heterozygous means having different alleles
    • Inherited disorders
      • Inherited disorders are caused by faulty genes
      • Many personal and ethical issues are raised: in deciding to have a genetic test (a positive result could alter lifestyle, career, insurance), by knowing the risks of passing on an inherited disorder (whether to marry/ start a family)
      • inherited disorders are caused by faulty alleles, most of which are recessive
      • It is possible to predict the probability of inheriting such disorders by interpreting genetic diagrams
  • Genetic variation is caused by: Mutations, which are random changes in genes or chromosomes
    • rearrangement of genes during the formation of gametes
      • Fertilisation, which results in a zygote with alleles from the father and mother

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