Inheritance: Part 2

If you inherit two copies of every gene, one from each parent, how do your cells know which version to use? Biology - Cells And DNA - Learning Points. Alleles, alternative forms of genes, can be dominant or recessive. Dominant alleles will always be expressed even if only one copy is present. Recessive alleles will only be expressed if both copies are present. Cystic Fibrosis is a genetic condition caused by a recessive gene. Huntington's Disease is a condition caused by a dominant allele. A Twig Curriculum Film. Delivering key learning points. Get straight to the facts in just three minutes – directly linked to core learning, Twig's curriculum films will fit neatly into your lesson plans.