Monohybrid inheritance and sex linkageEdexcel International A Level Biology: Mind map

Exam questions on Monohybrid inheritance and sex linkage

1. Cystic fibrosis is caused by a recessive allele, f, of a single gene on an autosome. The dominant allele is F. Two parents who do not have cystic fibrosis are expecting a child, and the couple already have one child who has cystic fibrosis.
   Explain how two parents who do not have cystic fibrosis can have a child who has the condition.2 marks
2. In a breed of cattle, coat colour is controlled by one gene with two alleles, $C^{R}$ (red hairs) and $C^{W}$ (white hairs). Neither allele is dominant. Cattle with the genotype $C^{R}C^{W}$ have a roan coat, with both red and white hairs.
   A roan bull is crossed with a white cow. Give the genotypes of the possible calves and the expected ratio of their phenotypes.2 marks
3. A rare inherited condition is studied in a family. Neither individual 1 (a man) nor individual 2 (a woman) has the condition. They have three children: individual 3, a daughter who has the condition, and individuals 4 and 5, two sons who do not have the condition.
   Deduce the mode of inheritance of this condition, using evidence from the family.3 marks