Cystic Fibrosis

Question 1

cystic fibrosis

Answer 1

a serious genetic disease caused by a recessive allele which affects the production of mucus by epithelial cells

Question 2

exocrine glands

Answer 2

glands which produce substances and secrete them to where they are needed through a small tube call a duct

Question 3

villi

Answer 3

finger-like projections of the lining of the small intestine which increase the surface area for the absorption of digested food

Question 4

duodenum

Answer 4

the first part of the gut (small intestine) after the stomach

Question 5

pancreatic duct

Answer 5

the duct from the pancreas which carries digestive enzymes made in the pancreas into the duodenum

Question 6

insulin

Answer 6

a hormone made in the pancreas involved in the regulation of blood sugar levels

Question 7

explain how mutations result in CF

Answer 7

• the mutation is in the gene coding for the CFTR protein

• therefore the CFTR does not function correctly

• resulting in very thick sticky mucus

Question 8

Suggest why cells from mouth swabs or blood samples are used rather than gametes?

Answer 8

1. these cells are easy to collect
2. a relatively large number of cells can be collected
3. they contain diploid cells
4. any alleles/ mutations will be present in them

Question 9

Explain why it is necessary to test for several different recessive alleles in the screening for cystic fibrosis.

Answer 9

• CF results from one of a number of possible mutations of this gene
• testing for only one will miss other recessive alleles

Question 10

If neither partner is a carrier then it is considered that the chance of having a child with cystic fibrosis is low. Explain why the probability of having a child with cystic fibrosis is low and NOT zero.

Answer 10

• false negatives exist
• mutation may occur in the formation of the gametes
• mutation in both gametes
• mutation may occur after fertilization

Question 11

If one of the partners is found to be a carrier then screening for cystic fibrosis may be offered to other family members. Explain why this screening is offered to other family members.

Answer 11

• any other family member could be a carrier (genetic disease)
• choices can be made about having children

Question 12

In which case is screening used before implantation?

Answer 12

Couple who are both carriers use IVF and embryos are screened.

Only embryos free from the defective gene are used.

Question 13

what are ethical/social issues with IVF?

Answer 13

• religious or other objections to destroying embryos
• IVF is expensive and not very reliable

Question 14

In which case is screening used to identify carriers?

Answer 14

When someone who has family members with CF would like to have a baby.

Question 15

what are ethical issues with identifying carriers?

Answer 15

If positive the person must decide whether or not to go ahead with natural pregnancy or other options.

Question 16

when is parental screening carried out?

Answer 16

When woman is already pregnant and there is a risk that the child might have CF.

Question 17

what are ethical issues with parental screening?

Answer 17

• decision making/abortion or not
• chance of gene therapy in the future
• testing could cause miscarriage
• results are nit 100% accurate
• false negative / false positive

Question 18

Describe how one method of parental screening can be carried out.

Answer 18

1. chorionic villus sampling/ amniocentesis
2. fetal cells are obtained from the placenta/ amniotic fluid
3. cells tested for presence of CFTR /faulty allele