Module 6

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

Self-Check

To practise “probabilities,” complete the following questions. The questions allow you to express your answer as a fraction, a decimal, or a percentage. Remember to read the question on the Diploma Exam carefully. It will specifically state the format that your answer must take.

SC 1. The ability to taste the chemical PTC is determined by a single gene in humans, with the ability to taste PTC indicated by the dominant allele T, and the inability to taste PTC by the recessive allele t. Suppose two heterozygous tasters (Tt) have a large family.

1. Predict the proportion of their children who will be tasters and non-tasters. Use a Punnett square to illustrate how you made this prediction.
   
   
2. What is the likelihood that their first child will be a taster? What is the likelihood that their fourth child will be a taster?
   
   
3. What is the likelihood that the first three children of this couple will be non-tasters?

SC 2. A husband and wife are both heterozygous for a recessive gene, c, for albinism. They were informed that the twins they are expecting are dizygotic, a boy and a girl.

1. Draw a Punnett square of this cross.
2. What are the chances that one child will be albino?
3. What are the chances that both children will be normal?
4. What are the chances that both babies will have the same phenotype for skin pigmentation?