Inherited disorder

• Cystic fibrosis is a disorder that mainly affects the lungs, pancreas, liver, and intestine
• Main symptom is difficulty breathing
• Caused by a faulty recessive allele on chromosome 7
• To be born with cystic fibrosis, a child has to inherit two copies of the faulty gene - one from each parent
• Parents of a child with cystic fibrosis are usually carriers of the faulty gene, but do not have the condition themselves
• Genetic diagram shows:

  • Homozygous individual (ff) will develop cystic fibrosis
  • Heterozygous individual (Ff) will be a carrier, but not develop the condition
  • Homozygous with dominant allele (FF) will not develop cystic fibrosis
• Example 1:

  • Both parents are heterozygous (Ff)
  • Chance of producing a child with cystic fibrosis is 1 in 4 or 25%
• Example 2:

  • Only one parent has a copy of the recessive allele (Ff)
  • No chance of producing a child with cystic fibrosis
  • Offspring ratio of FF to Ff is 1:1 or 50%
• Polydactyly is an inherited condition where a person has extra fingers or toes
• Caused by a dominant allele of a gene
• Homozygous (PP) or heterozygous (Pp) for the dominant allele will develop polydactyly
• Offspring need to carry just one dominant allele from their parents to inherit the condition
• Probability of offspring having polydactyly is 50% and 50% not having it
• Genetic testing involves analysis of a person's DNA to see if they carry alleles that cause genetic disorders
• Can be done at any stage in a person's life
• Antenatal testing is used to analyse an individual's DNA or chromosomes before they are born
• Neonatal testing involves analysing a sample of blood from a baby's heel to detect genetic disorders early
• Pre-implantation genetic diagnosis (PGD) is used on embryos before implantation to ensure healthy embryos are implanted