Wrap-up Questions

1. In addition to the coat coloration genes discussed in this chapter, other genes affect patterns like saddle markings and other black/tan patterns. The “Dominant Black” allele, K, overpowers the effects of several patterning genes, making a dog mostly black in color regardless of the alleles at those other genes. Thinking about the language of genetics, from the Allele Interactions and Multigenic Inheritance modules, explain why the name “Dominant Black” is a misleading way of describing this phenotype.

2. The Cu locus determines whether a dog has a curly or straight coat (Curly is incompletely dominant to straight). The L locus determines whether a dog has a long or short coat (Short is dominant to long). However, a dog with a short coat is likely to have straight fur, regardless of its genotype at the Cu locus.

  1. How would you describe the relationship of the Cu and L loci?
  2. What is the phenotype of a dihybrid dog?
  3. Predict the phenotypic ratio of the F1 offspring of two dihybrid dogs.

3. Chickens have fleshy protuberances called combs on the top of their heads. Combs can come in shapes called “single”, “rose”, “pea” and “walnut”, shown in Figure 18. Two chickens with walnut combs are crossed, with offspring counted over multiple years. The F1 offspring are listed below.

  • A picture of four roosters with different shaped combs. A single comb has one row of tall, spiky extensions extending to the back of the head. A rose comb is shorter with a field of short protrusions. A pea comb is flatter with ridges and bumps. A walnut comb is short and round, protruding only over the beak of the bird.27 Walnut chicks
  • 10 Pea chicks
  • 9 Rose chicks
  • 3 Single chicks

Give the genotypes of the parents and the F1 offspring. Use an underscore to indicate where multiple alleles might be possible.

4. You’ll recall that early scientists studying heredity hypothesized that the “blending hypothesis” would explain how traits of parents might be transmitted to offspring. Explain how QTLs work to support and contradict the blending hypothesis. For example: why might a very tall parent and a very short parent be expected to have a child of medium height? But how might two medium-height parents have a very tall kid?

5. The table below shows the results of a complementation test in English bluebells. Wildtype bluebells are blue, but some varieties have white or pink flowers. How many complementation groups are listed in this table? Based on the result of this test, how many genes control flower color in bluebells?

Strain 1










1: White WhiteWhite bluebell flower No Data No Data No Data No Data
2. White WhiteWhite bluebell flower WhiteWhite bluebell flower No Data No Data No Data
3. White BlueBue bluebell flower BlueBue bluebell flower WhiteWhite bluebell flower No Data No Data
4. Pink BlueBue bluebell flower BlueBue bluebell flower BlueBue bluebell flower PinkPink bluebell flower No Data
5. Pink BlueBue bluebell flower BlueBue bluebell flower BlueBue bluebell flower PinkPink bluebell flower PinkPink bluebell flower

[Wrote the color names in, due to limited ability to add images to tables. Would it be better to create an image of the original table?]

6. In this module, we discussed how recessive homozygosity at the “e” locus results in a dog with yellow, cream, or reddish fur. These dogs are all true-breeding: a cross between two yellow labrador retrievers always gives yellow puppies.  However, when certain reddish-yellow dogs are interbred with other reddish-yellow dogs known to have the “ee” genotype, the litters have dark-colored puppies. Propose an explanation for this result.

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