5.In a certain genetic cross, 1/16 proportion of progeny shows mutant phenotype. It means
(1) Two independent assorting genes are involved for trait
(2) Two independently assorting duplicate genes are involved
(3) Two linked genes are involved for trait
(4) Two independent segregating alleles responsible for trait

The observation that 1/16 of the progeny shows a mutant phenotype generally indicates two independently assorting genes with recessive alleles both required to show the mutant trait. This is consistent with option (2): “Two independently assorting duplicate genes are involved.”

Explanation with Genetic Principles

When two genes independently assort and have duplicate gene action (also called duplicate dominant epistasis), the presence of at least one dominant allele from either gene produces the wild type or normal phenotype, and only the double homozygous recessive genotype (aabb) shows the mutant phenotype. The expected phenotypic ratio for such duplicate genes is 15 normal : 1 mutant (where the mutant phenotype is 1/16).

• For duplicate genes, each gene can compensate for the loss of the other; thus, the mutant phenotype appears only when both genes are homozygous recessive.

• This explains the 1/16 proportion of mutant progeny.

Explanation of Other Options

• (1) Two independently assorting genes involved for a trait usually produce a 9:3:3:1 ratio in a dihybrid cross, not 1/16 for mutants.

• (3) Two linked genes would not assort independently and thus would not produce exact Mendelian ratios like 1/16 mutant.

• (4) Two independently segregating alleles responsible for the trait suggest a monogenic trait or simple inheritance, which typically results in phenotypic ratios like 3:1 or 1:2:1, not 1/16 for mutant phenotype.

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Introduction

The occurrence of 1/16 mutant phenotype in genetic crosses is a hallmark of duplicate gene interaction where two independently assorting genes work redundantly. This article explains how such a 1/16 ratio arises and guides you to identify the underlying genotype interaction responsible for this genetic pattern.

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Genetic Basis of 1/16 Mutant Phenotype Ratio

In duplicate gene action, two genes produce the same phenotype when at least one dominant allele of either gene is present. The mutant phenotype appears only when both genes are homozygous recessive (aabb). The resulting F2 generation classically displays a 15:1 ratio of wild type to mutant, meaning 1/16 of the progeny exhibit the mutant phenotype.

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Why Duplicate Genes and Independent Assortment?

The 1/16 mutant frequency indicates that each gene independently segregates into gametes, following Mendel’s law of independent assortment. However, the duplicate nature means that the genes have redundant functions, and the loss of function in one gene is compensated by the other unless both are recessive.

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Evaluation of Other Options

• Two independently assorting genes for a trait in a classic dihybrid cross will show a 9:3:3:1 ratio, not 1/16 mutant phenotype.

• Linked genes do not assort independently and distort Mendelian ratios.

• Independent segregation of alleles responsible for a trait generally produces a simpler ratio (e.g., 3:1) and not the rare 1/16 mutant.

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These insights help grasp how multiple genes interact to control traits and predict phenotypic ratios, crucial for genetics studies and competitive exam preparation.