Chapter 9 Study Questions
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- Compare the terms “recombination” and “crossover”. How are they similar? How are they different?
- Explain why it usually necessary to start with pure-breeding lines when measuring genetic linkage by the methods presented in this chapter.
- Suppose you knew that in a population, a trait (allele at a locus) that dominantly affected earlobe shape was tightly linked to a trait that dominantly affected susceptibility to cardiovascular disease in humans. Under what circumstances would this information be clinically useful?
- In a previous chapter, we said a 9:3:3:1 phenotypic ratio was expected among the progeny of a dihybrid cross, in absence of gene interaction.
- What does this ratio assume about the linkage between the two loci in the dihybrid cross?
- What ratio would be expected if the loci were completely linked? Be sure to consider every possible configuration of alleles in the dihybrids.
- Given a dihybrid with the genotype CcEe:
- If the alleles are in coupling (cis) configuration, what will be the genotypes of the parental and recombinant progeny from a test cross?
- If the alleles are in repulsion (trans) configuration, what will be the genotypes of the parental and recombinant progeny from a test cross?
- In this question, the white flowers (w) are recessive to purple flowers (W), and yellow seeds (y) are recessive to green seeds (Y). If a green-seeded, purple-flowered dihybrid is test crossed, and half of the progeny have yellow seeds.
- What can you conclude about linkage between these loci?
- What do you need to know about the progeny in this case?
- If the progeny of the cross aaBB × AAbb is test crossed, and the following genotypes are observed among the progeny of the test cross, what is the frequency of recombination between these loci?
AaBb 135
Aabb 430
aaBb 390
aabb 120 - What is meant by the sentence “All linked genes are syntenic, but not all syntenic genes are linked.”?
