Huntington's disease and cystic fibrosis are single gene disorders. Huntington's causes problems with muscle control and memory. Symptoms appear in middle age and worsen over time. Cystic fibrosis causes thick mucus to build up in the lungs and pancreas, leading to breathing issues and digestion problems. Both disorders are inherited in an autosomal recessive pattern, so carriers do not show symptoms but can pass the allele to their children.

8. Family tree- Huntington's Woman with Huntington’s Man with Huntington’s Woman without Huntington’s Man without Huntington’s Liam Kate Lisa Susan Sarah Karl Paul Emma Sean Alex Jo John

9. Family tree – Cystic fibrosis Rob David Shane Paula Jane Laura Keith Leon Owen Claire Sian Man with out cystic fibrosis Man with cystic fibrosis Woman without cystic fibrosis Woman with cystic fibrosis

11. Comparing family trees Ff or ……….. ............. What are the possible allele pairs of people without the disorder? …… .... HH or ……. What are the possible allele pairs of people with the disorder? Yes / No Yes / No Do the parents of the affected people also have the disease? Cystic fibrosis Huntington’s Name of disorder Key: H = Huntington's allele C = normal allele h = normal allele c = cystic fibrosis allele