The following progeny are obtained from a test cross of ...

Question

The following progeny are obtained from a test cross of a trihybrid wild-type plant to a plant with the recessive phenotypes compound leaves (c), intercalary leaflets (i), and green fruits (g). (Traits not listed are wild type.) The test-cross progeny are as follows:

Phenotype Number
Compound leaves 324
Compound leaves, intercalary leaflets 32
Compound leaves, green fruits 5
Compound leaves, intercalary leaflets, green fruits 51
Intercalary leaflets 3
Intercalary leaflets, green fruits 309
Green fruits 42
Wild type 49
815

Determine the order of the three genes, and construct a genetic map that identifies the correct order and the alleles carried on each chromosome in the trihybrid parental plant.

Accepted Answer

Hey, everyone. Let's take a look at this question together. In peat plants, flower, color, seed shape and pod shape are all controlled by different genes that assort independently suppose purple flowers dominate over white flowers, smooth seeds dominate over wrinkle seeds and inflated pods dominate over constricted pods. You perform a tri hybrid cross between two P plants with the following genotypes. Homozygous dominant A B and C and homozygous. Recessive A B and C. What are the expected genotypes and phenotypes of the F one generation? Is it answer choice? A, the genotype homozygous dominant A B and C and the phenotype purple, smooth and inflated answer choice B, the genotype heterozygous A B and C and the phenotype white, wrinkled and constricted answer choice. C the genotype heterozygous A B N C with the phenotype purple, smooth and inflated or answer choice. D the genotype homozygous recessive A B N C with the phenotype wrinkled and constricted. Let's work this problem out together to try to figure out what the expected genotypes and phenotypes are for the F one generation. So, since we are crossing a genotype, that is homozygous dominant for all three genes with another genotype that is homozygous recessive for all three genes, we know that a cross between homozygous dominant and homozygous recessive results in 100% of the offspring having a heterozygous genotype which we can see in upon it square where we cross that homozygous dominant with the homozygous recessive, we end up with 100% of the offspring having that heterozygous genotype. So we have 100% are heterozygous, which means that the expected genotype or the F one generation are all heterozygous. So we can go ahead and eliminate answer choices. A and answer choices. D since answer choice A says that the genotype will be homozygous dominant for all three genes. And answer choice. D says homozygous recessive for all three genes. So answer choices A and D are incorrect. And when it comes to the phenotype of the F one generation, since purple is dominant over white, smooth, is dominant, over wrinkled and inflated is dominant, over constricted. All of the dominant phenotypes will be present. So we will have a purple, smooth and inflated pea plant, which means that answer choice C that heterozygous genotype and the purple, smooth and inflated phenotype is the correct answer. Since we know that we are crossing a pea plant that is homozygous dominant for all three genes with another P plant that is homozygous recessive for all three genes. A cross between homozygous dominant and homozygous recessive will result in 100% of the offspring having that heterozygous genotype. Thus eliminating answer choices A and D and since purple, smooth and inflated is dominant over white, wrinkled and constricted, that means that answer choice C is the correct answer. Since the expected genotype and phenotype of the F one generation is heterozygous for all three genes and purple, smooth and inflated. I hope you found this video to be helpful. Thank you and goodbye.

Key Concepts

Gene Mapping

Test Cross

Recombination Frequency

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