The screening is done free by specialist hospitals for couples who are at risk of having

A man and a woman do not have CF.

The man and the woman have a child who has CF.

Draw a Punnett square diagram to find the probability that their next child will

have CF.

Use the symbols:

T = dominant allele

t = recessive allele

Draw a ring around the genotype of any children with CF.

Probability =

Embryo screening for CF can be done by two methods.

Method 1

• The woman becomes pregnant by sexual intercourse.

• After 10 weeks of pregnancy a fine needle is inserted into the uterus.

• A sample of the fluid surrounding the embryo is taken.

• The DNA of the embryo is tested for CF.

The screening is done free by specialist hospitals for couples who are at risk of having