Module 6 Mendelian Genetics

Module 6—Mendelian Genetics and Inheritance

Read

From his work with peas, Mendel concluded that two kinds of factors control every trait, and that each individual has a pair of these factors; one inherited from the mother, and one from the father. In each case, one factor was dominant to the other. As you have just learned with spotting in cats and four-o'clock flower colour, exceptions to dominance exist. You may also not find it surprising to discover that more than two alleles may affect the same trait.

Multiple allelic traits are described in your textbook on pages 604, 605 and 606. Read these pages carefully before you proceed any further. As you do this reading, 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

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, then adding a superscript A or B if indicating one of the co-dominant alleles, and using a lower case i with no superscript for the recessive O allele. Complete questions #11, 13 – 15, and 17 on the bottom of page 606 of your textbook. Discuss your work with your instructor. Save your answers to your course folder.

Self-Check

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

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.
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.
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 colors in chickens?
   2. What offspring would you expect from the mating of a grey rooster and a black hen?
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?