Question

Which of the following statements are true?
A. When two or more genes co-exist on the same chromosome, they may violate the principle of independent assortment during meiosis.
B. Positive interference occurs when the presence of one chiasma increases the possibility of another chiasma occurring in the immediate vicinity.
C. The proportion of crossovers never exceeds 50%.
D. The Chi-square test can be used for segregation ratios and detection of linkage.
Choose the most appropriate answer from the options given below:

• A. A, B and D only
• B. A, B and C only
• C. A, B, C and D
• D. A, C and D only

Hint:

Remember the definitions of interference:

\textbf{Positive interference}: One crossover DECREASES the chance of another nearby (the common case).
\textbf{Negative interference}: One crossover INCREASES the chance of another nearby (rarer). \end{itemize} Think "positive" = inhibiting/suppressing effect.

Answer 1

The Correct Option is D

Step 1: Concept Overview:
This question tests knowledge of key genetics concepts: linkage, interference, recombination frequency, and the Chi-square test.

Step 2: Statement Analysis:
- Statement A: Correct. Linked genes reside on the same chromosome. They are typically inherited together, violating Mendel's Law of Independent Assortment.
- Statement B: Incorrect. This describes negative interference. Positive interference occurs when one crossover event {reduces} the likelihood of another nearby crossover.
- Statement C: Correct. Recombination frequency represents the proportion of recombinant offspring. For linked genes, it ranges from 0% to 50%. A 50% recombination frequency mirrors independent assortment (seen with genes on different chromosomes or far apart on the same chromosome) and is the upper limit.
- Statement D: Correct. The Chi-square (\(\chi^2\)) test is a statistical test of goodness-of-fit. Genetics commonly uses it to compare observed phenotypic ratios to expected ratios under a specific hypothesis (e.g., Mendelian ratios like 9:3:3:1). Significant deviations suggest the hypothesis is wrong, potentially indicating linkage.

Step 3: Conclusion:
Statements A, C, and D are correct; statement B is incorrect. Therefore, the answer is (D).