6.1.7: Inherited disorders
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Some disorders are inherited.
Inherited disorders are caused by the inheritance of certain alleles.
Polydactyly is having extra fingers or toes and is caused by a dominant allele.
Cystic fibrosis is a disorder of cell membranes and is caused by a recessive allele.
Embryo screening and gene therapy may alleviate suffering but can raise economic, social and ethical issues.
Judgement example: embryo screening may reduce the chance of a child inheriting cystic fibrosis, but some people object to selecting embryos.
Common exam mistakes
Polydactyly is caused by a dominant allele, while cystic fibrosis is caused by a recessive allele.
For recessive disorders, carriers have one recessive allele but do not show the disorder.
In family-tree questions, use both phenotype and offspring evidence to infer a genotype.
Embryo screening evaluations need specific benefits and issues, such as avoiding serious disease, embryo destruction, cost, false results or ethical objections.