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Ch. 5 - Genetic Linkage and Mapping in Eukaryotes
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 5 - Genetic Linkage and Mapping in EukaryotesProblem 15d
Chapter 5, Problem 15d

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:
Table displaying phenotypes and counts of corn seedlings: tunicate, glossy, liguled; nontunicate, nonglossy, liguleless, etc.
If evidence of linkage is present, calculate the recombination frequency or frequencies from the data presented.

Verified step by step guidance
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Step 1: Understand the problem. This is a trihybrid cross involving three traits: tunicate seed (T), glossy appearance (G), and liguled stem (L), each with dominant and recessive alleles. The trihybrid plant (TtGgLl) is crossed with a homozygous recessive plant (ttggll). The goal is to determine if there is evidence of linkage between any of the genes and, if so, calculate the recombination frequency.
Step 2: Identify parental and recombinant phenotypes. Parental phenotypes are those that match the original combinations of alleles in the parents (T-G-L- and ttggll). Recombinant phenotypes are those that result from crossing over, leading to new combinations of alleles. From the data, identify which phenotypes are parental and which are recombinant.
Step 3: Calculate the total number of parental and recombinant offspring. Add the counts of the parental phenotypes together and the counts of the recombinant phenotypes together. This will help determine the proportion of recombinants in the total population.
Step 4: Calculate the recombination frequency. The recombination frequency is calculated as the number of recombinant offspring divided by the total number of offspring, multiplied by 100 to express it as a percentage. Use the formula: Number of recombinantsTotal offspring × 100.
Step 5: Interpret the recombination frequency. If the recombination frequency is less than 50%, it suggests that the genes are linked and located on the same chromosome. If it is close to 50%, the genes are likely unlinked and assort independently. Use the calculated recombination frequency to determine the degree of linkage between the genes.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, where dominant traits mask the expression of recessive ones. This framework is essential for analyzing inheritance patterns in the corn seedlings, as it helps predict the phenotypic ratios expected from specific crosses.
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Linkage and Recombination

Linkage refers to the tendency of genes located close to each other on a chromosome to be inherited together. Recombination occurs during meiosis when homologous chromosomes exchange genetic material, leading to new allele combinations. The recombination frequency quantifies this exchange, providing insight into the genetic distance between linked genes, which is crucial for interpreting the results of the corn seedling cross.
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Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In this case, the observed phenotypes of the progeny plants can be analyzed to determine if they align with expected Mendelian ratios or indicate linkage. Understanding these ratios is vital for calculating recombination frequencies and assessing the genetic relationships among the traits studied.
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Related Practice
Textbook Question

In a diploid plant species, an F₁ with the genotype Gg Ll Tt is test-crossed to a pure-breeding recessive plant with the genotype gg ll tt. The offspring genotypes are as follows:

What is the order of these three linked genes?

Textbook Question

In a diploid plant species, an F₁ with the genotype Gg Ll Tt is test-crossed to a pure-breeding recessive plant with the genotype gg ll tt. The offspring genotypes are as follows:

Calculate the recombination frequency between each pair of genes.

Textbook 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:

Could all three genes be carried on the same chromosome? Discuss why or why not.

Textbook 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:

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

Textbook 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:

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

Textbook 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:

Using the gene symbols given above, write the genotypes of F₁ and F₂ plants.