In cucumbers, dull fruit (D) is dominant to glossy fruit (d), and orange fruit (R) is dominant to cream (r) fruit. The genes coding for dull and glossy assort independently from the genes coding for orange and cream. A plant that has dull and orange fruits is crossed to a plant that has dull and cream fruits. The cross produces 3/8 plants with dull and orange fruits, 3/8 plants with dull and cream fruits, 1/8 plants with glossy and orange fruits, and 1/8 plants with glossy and cream fruits. Give the genotypes of the parents and offspring of the cross.
For help with this problem
1. Review Section 3.3 Dihybrid Crosses Reveal the Principles of Independent Assortment
2. Review the steps used in Worked Problem 4 on pg XXX
Begin by thinking about the steps to take to do this problem. Using the numbers 1-6 place the following steps in order you would perform them to complete the problem.
| 0VV1JcqyBrI= | Identify the Question Being Asked |
| DYU2tVvtzEQ= | Determine the phenotypes and proportions expected among the progeny of the cross |
| h4XZagboIgc= | Separate the cross into two single locus crosses to asses the inheritance of each trait alone |
| yBhAQ+3VvjM= | Put genotypes for each locus together and determine the overall genotypes of the parents and offspring. |
| 607M7xmPORU= | Assign the genotypes you can infer from the phenotypes |
| XvVM00l89Is= | Write out the information given about the dominance relations of the traits and the allelic symbols for the traits. |
A common mistake when starting a problem is rushing ahead and not carefully reading the question. In this question for example, if you look quickly you might only give the genotypes of the parents, forgetting to also provide genotypes of the progeny. Reading carefully and identifying exactly what is asked is crucial to your success in answering these questions.
Using single letters, indicate the proper allelic symbol and letter you would use for each trait.
| Dull | DD7UQIIkhDI= |
| Glossy | ujZVRF1sK00= |
| Orange | k2tcaXUqHdo= |
| Cream | oUDghrXV/HA= |
Write down as much information about the genotype as can be inferred from the phenotype alone. Be sure to answer with Capital letters first, use an underscore symbol (_) to indicate a allele you can not know by phenotype alone and to address each trait in the order it is given (ie: dull first, than orange)
| dull, orange : rZmIeCyncRxc6bGncwowZA== | x | dull, cream : irSqm5pkwPj+Lc1O |
| ↓ | ||
| 3/8 dull, orange : rZmIeCyncRxc6bGncwowZA== | ||
| 3/8 dull, cream : irSqm5pkwPj+Lc1O | ||
| 1/8 glossy, orange : bA7hl/Bt5TnOQkhb | ||
| 1/8 glossy, cream : GyUEJIUyTziwkEel |
Did you write the genotype for write a genotype for dull as Dr or a genotype for dull and orange as Dr? A common mistake made in this problem is to forget that each genotype must have two alleles and alleles for texture and color must be kept separate. This goes back to the principles of segregation and independent assortment, so be sure to review those if you are confused!