1. Use the diagram to explain why cystic fibrosis is caused by a recessive allele.
Could the locus for the allele be on the X chromosome?

2. Coat colour in cats is controlled by a single gene
Coat colour in cats is controlled by a single gene. This gene has two alleles – B which results in black coloured fur and G which results in ginger fur.
Use the information above to explain why tortoishell cats are never male.

3. Tall, cut-leaved tomato plants are crossed with dwarf, potato leaved plants giving in the F1 generation nothing but tall, cut-leaved plants.
These are allowed to cross with each other producing in the F2 generation 926 tall, cut-leaved; 288 tall, potato-leaved; 293 dwarf, cut-leaved; and 104 dwarf, potato-leaved.

4. In fruit flies, normal wings are produced by the dominant allele M and miniature wings by the recessive allele m.
Pure-breeding, female flies with normal wings were crossed with male flies having miniature wings. All the offspring had normal wings.
The offspring were allowed to interbreed and the following results were obtained.
105 normal, females
52 normal, males
46 miniature-winged, males

6. Give evidence from the diagram that night blindness could be a recessive condition.
If night blindness is a recessive condition, explain why it cannot be sex linked.