Module 6

Module 6—Mendelian Genetics: The Transmission of Traits to the Next Generation

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 teacher.

 

In Unit A, Module 2, you were introduced to Emily, who suffered from familial multiple endocrine neoplasia type 1 (FMEN1). Her career goals and life plans were continually interrupted by her health issues involving her endocrine system. In this module you have come to understand how Emily inherited this disorder. You can reflect on why she and her husband have decided not to have a family knowing that Emily’s condition is autosomal dominant. Apply your knowledge of probability to explain how Emily has a 50% chance of passing the gene to her children.

 

To apply your understanding of probability, complete the following Self-Check questions.

 

Self-Check

 

Numerical Response

 

SC 3. 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?

 

Numerical Response

 

SC 4. 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?

 

Numerical Response

 

Use the following information to answer SC 5.

 

Cystic fibrosis is the most common genetic disorder among Caucasians, affecting one in 2000 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.

 

SC 5. 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.)

 

Numerical Response

 

Use the following information to answer SC 6.

 

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.

 

SC 6. 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.)

 

Use the following information to answer SC 7.

 

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 to their offspring.

SC 7. 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.

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

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

 

Reflect on the Big Picture

 

From the Big Picture, were you worried that you would become bald too if all the men in your family were balding? You noticed the variety of traits in your family. Now you appreciate how you might calculate your chances of inheriting those traits.

 

Using mathematical calculations to generate probabilities can help to predict the outcomes of various crosses quickly and accurately. However, doing so can be a real challenge for some students. If you found working with probabilities difficult, remember that you can also solve these kinds or problems by creating Punnett squares and carefully filling them in as you did in Lesson 4. You should now have a basic understanding of probabilities, which will enable you to easily report chances in the form of fractions, decimals, or percentages.

 

Module 6: Lesson 5 Assignment

 

Submit your completed Module 6: Lesson 5 Assignment to your teacher for assessment.

 

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