Three dominant traits of corn seedlings, tunicate seed (...

Question

Three dominant traits of corn seedlings, tunicate seed (T-), glossy appearance (G-), and liguled stem (L-), are studied along with their recessive counterparts, nontunicate (tt), nonglossy (gg), and liguleless (ll). A trihybrid plant with the three dominant traits is crossed to a nontunicate, nonglossy, liguleless plant. Kernels on ears of progeny plants are scored for the traits, with the following results:

Phenotype Number
Tunicate, glossy, liguled 102
Tunicate, glossy, liguleless 106
Tunicate, nonglossy, liguled 18
Tunicate, nonglossy, liguleless 20
Nontunicate, glossy, liguled 22
Nontunicate, glossy, liguleless 23
Nontunicate, nonglossy, liguled 99
Nontunicate, nonglossy, liguleless 110
500

Is there evidence of genetic linkage among any of these gene pairs? If so, identify the evidence.

Table showing phenotypes of corn seedlings and their counts for genetic mapping.

Accepted Answer

Hey, everyone. Let's take a look at this question together. Assuming we have three linked genes or specific plant. The allele for purple flowers are dominant over the white flowers. The allele for tall plants is dominant over short plants and the allele for smooth stems is dominant over the hairy. A test cross is performed by crossing a plant with big p little P big T little T big s little S genotype with the true breeding plant with little p little, P little T little T little s little S genotype. They yield the following progeny. What are the genotypes of the offspring containing the parental alleles? Is it A B C or D? Let's work this problem out together to try to figure out which of the following answer choices is the correct answer. So for this question, the offspring that have the parental alleles can be distinguished since they are the ones that are most numerous. And in this case, we can see we have one offspring with 50 individuals and one with 45 individuals. And the offspring with 50 individuals are purple, short and smooth and the offspring with 40 five individuals are white tall and hairy. And we know that the allele for purple is that dominant uppercase P. The allele for short is the recessive lowercase T. And the allele for smooth is the dominant uppercase S and then for the white, tall and Harry, we have that lowercase recessive P or white, the uppercase dominant T for tall and the lowercase recessive s for hairy. So our offspring, one has a genotype that is big, P little, P little, T, little T and big S little S and our second offspring as the genotype, little P little P big T little T and little S little S which we are able to determine the other allele or the genotypes of the offspring. Since we know what one offspring has, we're able to determine from the other offspring. And so that means that the genotypes of our parents are big, P little, P little, T, little T big, S little S and little P little, P, big, T little T, little S little S which is answer choice. B big, P little, P little, T, little T big, S little S and little P little P, big T, little T little S little S since those are the genotypes of the offspring containing the parental alleles. Making answer choice B the correct answer because we know that the offspring that have those parental alleles are the ones that are most numerous. And in this case, the purple, short and smooth as well as the white tall and Harry are the most numerous. And we note that the purple, short and smooth phenotype is denoted by the dominant P, the recessive T and the dominant S and the white toll. And Harry phenotype is denoted by the recessive P, the dominant T and the recessive S alleles. So we are able to determine the genotypes based on the two most numerous phenotypes which gives us the genotypes of the offspring that contain the parental alleles. So, answer choice B is the correct answer. I hope you found this video to be helpful. Thank you and goodbye.

Key Concepts

Genetic Linkage

Trihybrid Cross

Phenotypic Ratios

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