- 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?
- What is meant by the sentence “All linked genes are syntenic, but not all syntenic genes are linked.”?