Question

1) You have been hired as a genetic counselor. Your first patient is a young woman named Lei who comes to you because her brother has cystic fibrosis. (Learn more about this disease in the PowerPoint slides – find out how it is inherited, is it dominant or recessive?) Lei is healthy but would like to know the risk that she is a carrier for the disease. Both her parents are healthy as is her older sister. a. Fill in the Punnett Square below with her parent’s genotypes to predict her risk of being a carrier of cystic fibrosis. You should be able to determine her parent’s genotypes from information given above. Male/ Female b. Explain to Lei her risk of being a carrier: 2). A blood DNA test for the cystic fibrosis allele becomes available and you recommend to Lei that she take the blood test and that her Fiancé Robert take the test as well. Lei’s test shows that she is a carrier. Robert is not. What is the risk that their future child will have cystic fibrosis? a. Use the Punnett Square below to predict Lei and Robert’s risk of having a child with CF? Male/ Female b. Write down your explanation to Lei and her Fiancé: 3. Another patient, Mark, comes to you because his father has just been diagnosed with the rare genetic disorder known as Huntington’s disease. Mark would like to know his potential risk of developing the disease (you must read about the inheritance pattern of Huntington’s disease in the Lecture and online games to answer this correctly!). Assume that his mother is showing no signs of Huntington’s disease. a. Fill in the Punnett Square below to predict Mark’s risk of getting Huntington’s disease. Male/ Female b. Your explanation to Mark:

Answer 1

Answer:

1).

Cystic fibrosis is an autosomal recessive disorder.

CC or Cc = normal

cc = Cytstic fibrosis

a). Lie is normal and her brother has disease. It means that her parents are both carriers for the disease. So that the parent’s genotype, Cc

Cc(mother) X Cc (Father)-----Parents

	C	c
C	CC (normal)	Cc (normal)
c	Cc (normal)	cc (cystic fibrosis)

Homozygous normal = CC = ¼

Carriers = ½

Diseased = ¼

b). As the both parents of Lie are carries, the chance of Lie is carrier for the diseas is ½.

2).

a). Lie (Cc) x Robert (CC)----Parents

	C
C	CC (normal)
c	Cc (normal)

There is no chance of the Lei and Robert’s child is having CF.

b).

Lie is carrier and based on DNA test Robert is homozygous normal. So there is 50% of their children will have disease.

3). Huntington’s diseas is an autosomal dominant diseas.

Normal = hh

Huntington = HH or Hh

a&b). Based on the information, Mark mother is normal with hh genotype.

If his father is homozygous, the Robert will have disease as below.

Father (HH) x mother (hh)-----Parents

	h
H	Hh (Huntington)

If his father is heterozygous, the Robert will have 50% chance of disease as below.

Father (Hh) x mother (hh)-----Parents

	h
H	Hh (Huntington)-1/2
h	hh (normal)-1/2