QQuestionBiology
QuestionBiology
A 9:3:3:1 ratio of phenotypes in the F^2 generation of a dihybrid cross:
A. indicates that the dihybrid cross is basically equivalent to two independent monohybrid crosses.
B. holds true only for genes on the same chromosome.
C. is not indicative of independent assortment.
D. indicates that an epistatic relationship exists between the two genes under investigation.
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Answer
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Step 1:Let's solve this step by step:
Step 2:: Understanding Dihybrid Cross Ratios
The 9:3:3:1 phenotypic ratio is a classic result of a dihybrid cross between two heterozygous parents where genes are independently assorting.
Step 3:: Analyzing the Ratio Components
- 9 parts: Represents individuals with dominant alleles at both gene loci - 3 parts: Represents individuals with dominant allele at one locus, recessive at the other - 3 parts: Represents individuals with recessive allele at one locus, dominant at the other - 1 part: Represents individuals with recessive alleles at both loci
Step 4:: Genetic Principle
This ratio is a direct result of independent assortment, where genes on different chromosomes segregate independently during gamete formation.
Step 5:: Evaluating the Options
- Option A is CORRECT: The 9:3:3:1 ratio demonstrates that the two genes are behaving like independent monohybrid crosses. - Option B is incorrect: This ratio occurs for genes on different chromosomes, not genes on the same chromosome. - Option C is incorrect: This ratio specifically indicates independent assortment. - Option D is incorrect: This ratio does not suggest an epistatic relationship.
Final Answer
A - The 9:3:3:1 ratio indicates that the dihybrid cross is basically equivalent to two independent monohybrid crosses.
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