Question

Study the figures given below and answer the questions.

Identify in which of the crosses the strength of linkage between the genes is higher. Give reason in support of your answer.

Hint:

Closer genes are separated less by crossing over; the genes in Cross A are closer, so linkage is higher there.

Answer 1

Step 1: Read the figure:
Cross A shows the genes for yellow body (y) and white eye (w). They sit very close together on the X chromosome.
Cross B shows the genes for white eye (w) and miniature wing (m). They sit far apart on the X chromosome.

Step 2: Recall the rule:
Morgan showed that linked genes lie on the same chromosome. The closer two genes are, the less often crossing over separates them.
So a short distance means strong linkage, and a long distance means weak linkage.

Step 3: Apply the rule:
In Cross A the genes y and w are close together. Crossing over between them is rare. They stay together and show tight linkage.
In Cross B the genes w and m are far apart. Crossing over takes place often between them, giving more recombinants.

Final Answer:
Linkage is stronger in Cross A, because the genes y and w lie very close together on the chromosome and are rarely separated by crossing over.