Brainlag PlusPolydactyly and cystic fibrosis, carriers, chances for a couple's children, and the arguments for and against screening embryos.
Two inherited disorders
Polydactyly (extra fingers or toes) is caused by a dominant allele, P.
One copy is enough, so there are no healthy carriers: Pp and PP both have it.
Cystic fibrosis is a disorder of cell membranes caused by a recessive allele, f. Only ff has it. Ff people are carriers: they do not have the disorder but can pass on f.
- Two carriers: Ff × Ff
- Boxes: FF, Ff, Ff, ff
- Cystic fibrosis (ff): 1 of 4 = 25%
- Carrier (Ff): 2 of 4 = 50%
A carrier does not have the disorder. When asked for the chance of a carrier, count only the Ff boxes.
The rest of this lesson and its 10 practice questions are in Plus.
Screen 1 of 2, free to read.
- 10 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards