Lesson 3.6.5

3.6.5 page 5

Reflect and Connect

By conducting the lab on coin tosses you should have been able to make the connection between probabilities in genetics and everyday events. It takes some practice, but probabilities can help solve genetics problems faster than writing out complete Punnett squares. To practice your skills, complete the following questions and check your answers. If you are encountering any difficulty, consult with your instructor.

 

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

 

Numerical Response

  1. A dominant allele, XE, carried on the X chromosome, causes the formation of faulty tooth enamel, resulting in either very thin or very hard enamel. A woman heterozygous for faulty tooth enamel marries a man with normal tooth enamel. What is the probability that their first child will be a boy with normal tooth enamel?

Answer: _____________

 

Numerical Response

  1. In sheep, white wool is a dominant trait, and black wool is a recessive trait. In a herd of 500 sheep, 20 sheep have black wool. If two heterozygous sheep mated, what would be the probability of them having a white lamb?

Answer: _____________

 

Use the following information to answer the next question.

 

Cystic fibrosis is the most common genetic disorder among Caucasians, affecting one in 2 000 Caucasian children. The cystic fibrosis allele results in the production of sticky mucus in several structures, including the lungs and exocrine glands. Two parents who are unaffected by the disorder can have a child with the disorder.

 

Numerical Response

  1. These parents, who are unaffected by cystic fibrosis, are planning to have another child. What is the percentage probability that their next child will be affected by cystic fibrosis? (Record your answer as a whole number.)

Answer:          _____________ %

 

Use the following information to answer the next question.

 

Marfan syndrome is an autosomal-dominant disorder of humans. Affected individuals tend to be tall and thin. They have defects in the lens of the eye, and weak connective tissue around the aorta. Often, affected individuals excel in sports like volleyball or basketball, but it is not uncommon for people with this syndrome to die suddenly.

Numerical Response

  1. A man, heterozygous for Marfan syndrome, and a homozygous recessive woman have a child. What is the probability that the child will be affected by Marfan syndrome? (Record your answer as a value from 0 to 1, rounded to two decimal places.)

Answer:          _____________

 

Use the following information to answer the next question.

Scientists believe that a mutant form of an autosomal gene called BRCA1 may be associated with 5% to 10% of all cases of breast cancer. About 80% of women who inherit the gene in its defective form are likely to develop a cancerous breast tumor. Men who carry the faulty BRCA1 gene rarely develop breast cancer, but they may pass the gene on to their offspring.

 

A couple has two children, a girl and a boy. The mother has a single mutant gene for breast cancer; the father is not a carrier of the mutant BRCA1 gene.

  1. What is the probability that their daughter has inherited the mutant BRCA1 gene?

    1. 75%
    2. 50%
    3. 25%
    4. 0%

 

Lesson Summary

During this lesson, you were to consider the following focusing question:

  • How can ratios be used to analyze types of inheritance or to predict the possibility of a trait appearing in the next generation?

Through the practice questions and the coin toss lab you have been given the opportunity to practice doing just that. By adding or multiplying the probabilities of individual traits, you have been able to predict the possible phenotypic outcomes of the next generation for two or three different traits. This can help answer genetic problems much more quickly than drawing out large Punnett squares.