Genetics ^_^

Some information on genetics :)


  • Key terms
  • Cystic fibrosis
  • Huntington's disease

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Key Terms

Diploid - Organisms inherit two copies of each gene and chromosome (one form each parent - maternal and paternal)

Genotype - The genes an organism had and the alleles of those genes

Allele - Is where a gene can exist in different forms

Recessive allele - Only expressed in the homozygous state

Haploid - Cells or organisms have only one copy of each gene and chromosome

Heterozygous - Having two different alleles of a gene

Homozygous - Having two identical alleles of a gene

Dominant alleles - Expressed when homozygous or heterozygous

Phenotype - The characteristics of an organism, including the enzymes and substances it produces. It depends on expression of the genotype and the interactions between genotype and environment

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Cystic Fibrosis (CF)

  • Sometimes referred to as Mucoviscidosis or CF
  • The incidence of CF varies in populations:
    • Asians - 1 in 10,000
    • Caucasians - 1 in 20-28
  • CF is an autosomal recessive mutation (over 500 different mutations of the CFTR gene have been identified:
    • Deletions, missense, nonsense, terminator codon
    • A mutation in the genotype (genetic characteristics) results in a mutation in the phenotype (physical characteristics)

Symptoms of CF:

  • Infertility occurs in both males and females
  • Disrupts the following glands:
    • Pancreas
    • Intestinal
    • Biliary tree (biliary cirrhosis)
    • Bronchial  glands (which can lead to chronic lung infections)
    • Sweat glands (high salt content which becomes depleted in hot environments)
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Phenylketonuria (PKU)



  • PKU is caused by a mutation of a gene on chromosome 12; it's caused by a recessive mutation
  • The gene codes for an enzyme called phenylalanine hydroxylase which breaks down phenylalanine into tyrosine
  • If phenylalanine isn't broken down, it builds up to a dangerous level and can cause brain damage
  • At birth, babies are tested for PKU by analysing a small sample of blood taken from a pin ***** at the heel. If the test is positive, the baby is put on a diet which doesn't contain any phenylalanine
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Huntington's Disease

  • Sometimes referred to as Huntington's chorea or HD
  • It's an uncommon genetic disease with an incidence of 1 in 20,000 people
  • It is an autosomal dominant mutation of a HD gene (IT15) which is caused by an increase in the length.
  • It is a triplet mutation (triplet stutter) when CAG is repeated approximately 40 times more than in none-sufferers
  • The Huntington's protein tends to break up into pieces, which then clump together
  • The clumped protein builds up in the nuclei of the brain cells, which either impairs or kills them
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;) xxxx

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