Use the diagram to explain why cystic fibrosis is caused by a recessive allele.

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. 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.