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 independent assortment 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 for a specific plant. The allele for purple flowers are dominant over the white flower. The allele for tall plants is dominant over short plants and the allele for smooth stems is dominant over the hairy stems. A test cross, it's performed by crossing a plant with that heterozygous P, heterozygous T and heterozygous S genotype with the true breeding plant with the homozygous recessive P, homozygous recessive T and homozygous recessive S genotype. They yield the following progeny. Which of the following gives the correct gene sequence. Is it answer choice. A gene P gene S gene T, answer choice B gene S gene P, gene T, answer choice C gene T gene P gene S or answer choice D gene S gene T gene P. Let's work this problem out together to try to figure out which of the following answer choices, gives the correct gene sequence. So from the progeny, we are able to determine the offspring that have the parental alleles and the offspring that are the double crossovers. And so the offspring that have the parental alleles are the ones that are the most numerous. So we have our purple, short and smooth that have 50 and we have our white tall and hairy that have 45. So this is our parent, one and our parent two and the offspring that are the double crossovers are the least numerous. So that is our purple, short and hairy, which has two and our white tall and smooth, which has 10. So we have our double crossover or DC O for short one and our double crossover or D CO2. And so using the shorthand identification for each allele, we can determine that pair one has that uppercase dominant P for purple, the lowercase recessive T for short and the upper case dominant S for smooth. And our parent two has the lower case recessive P for white, upper case dominant T for tall and lowercase recessive S for Harry. And our double crossover one has that uppercase dominant P for purple, the lower case recessive T for short and the lowercase recessive S for Harry. And our double crossover two has that lowercase recessive P for white, that uppercase dominant T for tall and the upper case dominant S for smooth. So we have our parent one, our parent two, our double crossover one and our double crossover two, which we can identify the parents by the shorthand abbreviations for that purple, short and smooth and our parent two for the white, tall and hairy. And then our double crossover one is purple, short and hairy. And our double crossover two is white, tall and smooth. And we can see that from parent one to the double crossover one, they share the same color and height. And from our parent two to our double crossover two, they share the same color and height as well. And the only differences between the two from the parent to the double crossover is the gene S which means that gene s will be at the center of the gene sequence. And looking at our answer choices, there is only one answer choice in which gene S is at the center of the gene sequence. So answer choice. A gene P followed by gene S followed by gene T is the correct answer. Because from the yield of the progeny, we are able to determine the parent one and parent two as well as the double crossover one and two. And we can see that parent one and double crossover, one share the same allele for color and height. And parent two share the same allele for color and height. And the double crossovers differ in that gene S. So gene S is at the center of the gene sequence, which by process of elimination, we can eliminate answer choice BC and D since they do not have gene S at the center of the gene sequence and answer choice A which has gene S at the center of the sequence is the correct answer because the correct gene sequence is gene P followed by gene S followed by gene T, which is answer choice. A, I hope you found this video to be helpful. Thank you and goodbye.

Key Concepts

Independent Assortment

Phenotypic Ratios

Trihybrid Cross

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