Q.65 The gene transmission from a male parent to a female offspring (“child”) to a male “grandchild”
is called:
1. crisscross inheritance
2. X linked inheritance
3. Y linked inheritance
4. Chromosomal inheritance
The gene transmission pattern from male parent → female offspring → male grandchild is called crisscross inheritance, characteristic of X-linked traits.
Correct Answer: 1. Crisscross Inheritance
In X-linked inheritance, fathers pass their X chromosome exclusively to daughters (who become carriers), while daughters transmit the X-linked gene to 50% of their sons (grandsons of the original father). This creates the diagnostic “skipping” pattern across generations and sexes: affected male → unaffected carrier daughter → affected grandson.
X-Linked Transmission Diagram
Affected Father (XᵃY) × Mother (XX)
↓
Daughters: Carriers (XᵃX) | Sons: Normal (XY)
↓
Grandsons: 50% Affected (XᵃY) | Granddaughters: 50% Carriers
Classic examples: hemophilia, color blindness, Duchenne muscular dystrophy.
Explanation of All Options
| Option | Description | Matches Pattern? |
|---|---|---|
| 1. Crisscross Inheritance | X-linked pattern: male→daughter→grandson. | Correct: Describes diagonal sex-specific transmission. |
| 2. X-linked Inheritance | General term for X chromosome genes. | Partial: Describes mechanism, not specific pattern name. |
| 3. Y-linked Inheritance | Father→son only (holandric). | Incorrect: Y skips daughters entirely. |
| 4. Chromosomal Inheritance | Any chromosome-based transmission. | Too vague; doesn’t specify pattern. |
