Observe the figure. Which symbol used in human pedigree analysis is l…

The correct answer is Option (2) → Parents with male child affected with disease

The figure (A) shows a square (male) and a circle (female) joined by a horizontal line, which marks the parents. A vertical line drops from it to a filled square. A filled symbol means an affected individual, and a square is a male, so (A) shows parents with a male child affected with disease.

Option (1) Mating between relatives — Incorrect. Mating between relatives is drawn as a square and circle joined by a double line, with no child below.

Option (2) Parents with male child affected with disease — Correct. Parents above, joined by a line, and an affected (filled) male child below is the NCERT symbol for parents with a male child affected with disease.

Option (3) Parents with female child affected with disease — Incorrect. An affected female child would be a filled circle. The child in (A) is a square.

Option (4) Parents with an unaffected male child — Incorrect. An unaffected child is drawn as an open (unfilled) symbol. The square in (A) is filled, so the child is affected.

Note: The whole question is drawn, not written. Figure 4.13 hides a set of easy marks for anyone who has looked at its symbols even once, so give it that look.

NCERT Extract:
Pedigree Analysis – “… In the pedigree analysis the inheritance of a particular trait is represented in the family tree over generations. In human genetics, pedigree study provides a strong tool, which is utilised to trace the inheritance of a specific trait, abnormality or disease. Some of the important standard symbols used in the pedigree analysis have been shown in Figure 4.13.”

Figure 4.13 Symbols used in the human pedigree analysis