Inherited DiseasesAn inherited disorder that causes great suffering is Huntington’s chorea, also known as Huntington’s disease. The disease usually develops between the ages of 35 and 45. With this disease the central nervous system gradually degenerates, leading to death. There is no cure at this time. The condition is genetically dominant.

1. A. The famous folksinger Woody Guthrie died from Huntington’s disease. He had several children including a son Arlo.i) Complete the Punnett square for Arlo’s parentsii) What is the probability that Arlo has Huntington’s

disease? 50%

b. When Clara is about to marry Patrick, she learns that her father has Huntington’s disease. She reads in the paper that a test to determine whether or not they will develop the disease was now available. Clara wants to know if she is likely to give her and Patrick’s children Huntington’s chorea. If you were in Clara’s position, would you take the test? Explain your reasoning.

Answers may vary. This is an old worksheet but there is still no cure for Huntingon’s disease

C. Suppose Clara does not take the test and instead takes the risk of having children who will develop Huntington’s chorea. Complete these Punnett squares for Clara’s children. Assume that Patrick does not carry the H gene.

d.

Find the probability that any one of Clara’s children will develop Huntington’s disease.

Woody Guthrie wrote the famous song “This land is our land”.

Woody Guthrie

H hArlo’s Mother

h Hh hhh Hh hh

H= gene for Huntington’s choreah = gene for not having the disease

Arlo Guthrie wrote “Alice’s Restaurant” It is long but worth a listen.

Patrick

h hClara H Hh Hh

h hh hh

H= gene for Huntington’s choreah = gene for not having the disease

Patrick

h hClara h hh hh

h hh hh

There is a ¼ or 25% chance that Clara’s children will develop Huntington’s disease.

e. When she is 27 years old. Clara has a baby named Brenda. When Brenda is 16, her mother is diagnosed as having Huntington’s chorea. What now is the probability that Brenda will eventually get the disease? There is now a ½ or 50% chance that Brenda will get Huntington’s disease.

2. Frances knows that her mother has Huntington’s disease. She deduces that at least one of her maternal grandparents was a sufferer.a. Is her reasoning correct? Yes because Huntington’s is a hereditary disease.b. Frances also deduces that at least one of her great-grandparents was a sufferer. Is she

correct? Yes she is correct.c. Frances researches her family history for Huntington’s disease.

d. Why doesn’t Frances extend her father’s tree? Her father did not have Huntington’s disease in his family.

e. Her diagram does not show a grandparent or a great-grandparent with the disease. Does this mean her deductions in a and b were wrong? Explain your answer.No, because both her grandfather and great grandmother on her mother’s side died young; so they could have had the gene for Huntington’s but did not live long enough to develop the disease.

f. In another family, Colin makes the family tree shown below. Who could yet develop Huntington’s chorea in this family? Cynthia, Patricia and Marilyn have parents with the disease and are too young to have developed the disease yet. They could develop in the future.

Died at 67

Died at 67Died at 28

Died at 80Died at 75Died at 24

Aged 47Aged 50

Frances (aged 20)

KEY

unaffected male unaffected female

male with disease female with disease

John Smith

(d)

Betty Jones

(d)

Jack Smith

(d)

Ivy Buddled

Pat McLeod Daisy

Smith (d)

Grace Hillan

(aged 75)

Paul Smith

(d)

Martin Smith

(d)

Terry Morton

(d)

Cynthia Smith

(aged 35)

Patricia McLeod

(aged 27)

Colin McLeod

(aged 48)

Marilyn Morton (aged 7)

(d) (d)

Vera Smith (aged 28)