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: Understanding the Concept:
This question assesses understanding of several key concepts in classical and statistical genetics, including linkage, interference, recombination frequency, and the Chi-square test.

Step 2: Analyzing each statement:
- Statement A: True. Genes located on the same chromosome are said to be linked. They tend to be inherited together and do not assort independently, which is a violation of Mendel's Principle of Independent Assortment.
- Statement B: False. This statement describes negative interference. Positive interference is the phenomenon where the occurrence of one crossover event (chiasma) {reduces} or suppresses the probability of a second crossover occurring nearby.
- Statement C: True. Recombination frequency is the proportion of recombinant offspring. For linked genes, it can range from 0% to 50%. A recombination frequency of 50% is the maximum possible and is equivalent to independent assortment (as occurs for genes on different chromosomes or very far apart on the same chromosome). A frequency cannot exceed 50%.
- Statement D: True. The Chi-square (\(\chi^2\)) test is a statistical goodness-of-fit test. It is commonly used in genetics to compare observed phenotypic ratios from a cross with the ratios expected under a certain hypothesis (e.g., Mendelian segregation ratios like 9:3:3:1). A statistically significant deviation from the expected ratio can indicate that the underlying hypothesis is incorrect, which can be used to detect linkage.

Step 3: Final Answer:
Statements A, C, and D are true, while statement B is false. Therefore, the correct option is (D).