Module 6

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

Read

From his work with peas, Mendel concluded that two factors control every trait, and that each individual has a pair of these factors; one inherited from the mother, and one from the father. One factor is dominant and the other is recessive. As you have just learned with spotting in cats and colours in four-o'clock flowers, exceptions to the dominant/recessive principle exist. Often more than two alleles may affect the same trait.

Carefully read “Multiple Alleles” and “Polygenic Inheritance” pages 604 to 607 in your textbook. Consider the adaptive advantages that multiple alleles might provide. Remember that variety contributes to biodiversity, and biodiversity is the key to the survival of species.

Try This

In Biology 20 you examined blood types A, B, AB, and O. In genetics, you have recognized these descriptions to be phenotypes of blood. Now you will examine the genotypes that produce these phenotypes. Examine the sample blood type problems on the top of page 606 of your textbook. Notice how they indicate alleles using a capital I as the letter base, and then add a superscript A or B if indicating one of the co-dominant alleles. A lower case i with no superscript represents the recessive O allele.

TR 12. Complete “Practice Problems” 11, 13 to 15, and 17 on the bottom of page 606 of your textbook. Discuss your work with your teacher and save your answers to your course folder.

Self-Check

Answer the following questions to check your understanding of the material in this lesson.

SC 1. In short-horned cattle, red is co-dominant with white. The hybrid is called roan. A roan mates with a roan. Use a Punnett square to determine the expected phenotypes of the offspring.

SC 2. The alleles for hair type show incomplete dominance. One allele (c) is for curly hair. Another allele (s) is for straight hair. The hybrid is wavy. A wavy-haired person marries a curly-haired person. Use a Punnett square to determine the expected phenotypes of their children.

SC 3. A rooster with grey feathers is mated with a hen of the same phenotype. Among their offspring, 15 chicks are grey, 6 are black, and 8 are white.

1. What is the simplest explanation for the inheritance of these colours in chickens?
   
   
2. What offspring would you expect from the mating of a grey rooster and a black hen?

SC 4. Colour patterns in a species of duck are determined by one gene with three alleles. Alleles H and I are semi-dominant (i.e., incomplete dominance), and allele i is recessive to both. How many phenotypes are possible in a flock of ducks that contains all of the possible combinations of these three alleles?