Ch. 4 - Gene Interaction

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 4 - Gene Interaction

Problem 35

Chapter 4, Problem 35

Cross-1 shown in the following figure illustrates genetic complementation of flower-color mutants. The produced from this cross of two pure-breeding mutant parental plants are dihybrid (CcPp) and have wild-type flower color. If these F₁ are allowed to self-fertilize, what phenotypes are expected in the F₂ , and what are the expected ratios of the phenotypes?

Verified step by step guidance

Step 1: Understand the genetic basis of the problem. The F₁ plants are dihybrid (CcPp), meaning they have one dominant and one recessive allele for each of two genes involved in flower color. The wild-type flower color in the F₁ indicates that the dominant alleles complement the recessive mutations from the parents.

Step 2: Determine the possible gametes produced by the F₁ dihybrid plants. Since the genotype is CcPp, the gametes can be CP, Cp, cP, and cp, each with equal probability (1/4).

Step 3: Set up a Punnett square to predict the genotypes of the F₂ generation by crossing the gametes from the F₁ plants with themselves. This will give you all possible combinations of the alleles C/c and P/p in the offspring.

Step 4: Assign phenotypes to each genotype based on the dominance relationships. Typically, the presence of at least one dominant allele in each gene (C and P) results in the wild-type flower color, while homozygous recessive combinations in either gene may produce mutant phenotypes.

Step 5: Calculate the expected phenotypic ratios by counting the number of genotypes corresponding to each phenotype from the Punnett square and expressing them as fractions or ratios of the total offspring.

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Key Concepts

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

Genetic Complementation

Genetic complementation occurs when two different mutations in separate genes produce a wild-type phenotype when combined in a heterozygote. This indicates that the mutations affect different genes, and each parent provides a functional allele for the gene mutated in the other, restoring the normal trait.

Dihybrid Cross and Mendelian Ratios

A dihybrid cross involves two genes, each with two alleles, and typically follows Mendel’s law of independent assortment. The F1 dihybrid (CcPp) self-fertilization produces an F2 generation with phenotypic ratios based on combinations of dominant and recessive alleles, often resulting in a 9:3:3:1 ratio for two independently assorting genes.

Phenotypic Expression of Flower Color Mutants

Flower color phenotypes depend on the interaction of alleles at two loci, where dominant alleles produce wild-type color and recessive alleles cause mutant colors. Understanding how combinations of C and P alleles affect pigment synthesis helps predict the expected phenotypes and their ratios in the F2 generation.

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Related Practice

Textbook Question

Epistatic gene interaction results in a modification of the F₂ dihybrid ratio.

What is the expected F₂ ratio?

Textbook Question

In rabbits, albinism is an autosomal recessive condition caused by the absence of the pigment melanin from skin and fur. Pigmentation is a dominant wild-type trait. Three pure-breeding strains of albino rabbits, identified as strains 1, 2, and 3, are crossed to one another. In the table below, F₁ and F₂ progeny are shown for each cross. Based on the available data, propose a genetic explanation for the results. As part of your answer, create genotypes for each albino strain using clearly defined symbols of your own choosing. Use your symbols to diagram each cross, giving the F₁ and F₂ genotypes. <>

Textbook Question

Epistatic gene interaction results in a modification of the F₂ dihybrid ratio.

What genetic principle is the basis of this expected F₂ ratio?

Textbook Question

Dr. O. Sophila, a close friend of Dr. Ara B. Dopsis, reviews the results Dr. Dopsis obtained in his experiment with iris plants described in Genetic Analysis 4.3. Dr. Sophila thinks the F₂ progeny demonstrate that a single gene with incomplete dominance has produced a 1:2:1 ratio. Dr. Dopsis insists his proposal of recessive epistasis producing a 9:4:3 ratio in the F₂ is correct. To test his proposal, Dr. Dopsis examines the F₂ data under the assumptions of the single-gene incomplete dominance model using chi-square analysis. Calculate and interpret this chi-square value. Can Dr. Dopsis reject the single-gene incomplete dominance model on the basis of this analysis? Explain why or why not.

Textbook Question

In a breed of domestic cattle, horns can appear on males and on females. Males and females can also be hornless. The following crosses are performed with parents from pure-breeding lines.

Explain the inheritance of this phenotype in cattle, and assign genotypes to all cattle in each cross.

Textbook Question

The wild-type allele of a gene has an A–T base pair at a particular location in its sequence, and a mutant allele of the same gene has a G–C base pair at the same location. Otherwise, the sequences of the two alleles are identical. Does this information tell you anything about the dominance relationship of the alleles? Explain why or why not.