Blood Relations – Study Notes
Reasoning Ability – IIT M.Tech Admission
1️⃣ Simple Explanation
Blood relations are the relationships that exist because of a common ancestor.
They are categorized mainly into direct (vertical) and collateral (horizontal) relationships.
| Term | Direct Relationship | Collateral Relationship |
|---|---|---|
| Father / Mother | Upward | — |
| Son / Daughter | Downward | — |
| Brother / Sister | Same generation | — |
| Uncle / Aunt | One generation above the sibling | — |
| Niece / Nephew | One generation below the sibling | — |
| Cousin | Same generation, sharing a common grand‑parent | — |
Rule of thumb – If you can trace a chain of parents/children between two persons, they are in a direct relationship.
If the chain includes a sibling step, they are in a collateral relationship.
2️⃣ Key Points & Definitions
| Concept | Definition | Example |
|---|---|---|
| Generation | A level in the family tree (e.g., parents are 1 generation above you). | You → Father (1 gen above) |
| Direct (Vertical) Relation | Involves only parent/child links. | You ↔ Mother, Mother ↔ Grand‑Mother |
| Collateral (Horizontal) Relation | Involves at least one sibling link. | You ↔ Aunt (mother’s sister) |
| Sibling | Two people who share both parents. | Brother, Sister |
| Half‑Sibling | Share only one parent. | Half‑brother, Half‑sister |
| Niece / Nephew | Child of a sibling. | Your brother’s son is your nephew |
| Uncle / Aunt | Sibling of a parent. | Your mother’s brother is your uncle |
| Cousin | Children of two siblings. | Your father’s brother’s son is your cousin |
| Consanguineous | Relation by blood. | All above except adopted or in‑law relations |
| Parental Deletion | Sometimes the word “parent” is omitted: e.g., “My father’s brother” = “my uncle” | |
| Parity Rule for Same Generation | If two persons are of the same generation, they are either siblings, cousins, or unrelated. | |
| Generation Difference Rule | If generation difference is 1 → parent/child; 2 → grand‑parent/grand‑child; 3 → great‑grand‑parent, etc. |
Quick Pointers for Reasoning Questions
- Identify the relationship chain from the statement.
- Count the number of “parent” links to find generational difference.
- Check for sibling steps to determine collateral relations.
- Use “half” qualifiers when only one parent is shared.
- Remember the terminology:
- “son of” vs. “daughter of” → gender matters.
- “sister of” vs. “brother of” → gender of the subject.
- When in doubt, draw a mini tree on paper.
3️⃣ Worked Example
Problem
In a family tree:
- A is the father of B.
- B is the mother of C.
- C is the son of D.
- D is the brother of E.
Find the relationship between A and E.
Solution
-
Trace the chain from A to E.
- A → B (father)
- B → C (mother)
- C → D (son)
- D → E (brother)
-
Count generations:
- A to B: 1 generation up.
- B to C: 1 generation down.
- C to D: 1 generation up.
- D to E: same generation (sibling).
-
Determine relationship
- From A to B: parent.
- From B to C: child.
- From C to D: parent.
- From D to E: sibling.
Simplify:
- A → B (parent) → C (child) → D (parent) → E (sibling).
- The net effect is: A is the great‑grandfather of E?
Wait – check again: - A → B (1)
- B → C (2)
- C → D (3)
So A is three generations above D.
Since D and E are siblings, they are at the same generation.
Therefore, A is three generations above E → great‑grandfather of E.
Answer: A is the great‑grandfather of E.
Check
- A (1) → B (2) → C (3) → D (4) → E (4).
- A is indeed 3 generations above E.
4️⃣ Quick Revision Summary
- Direct relations: parent ↔ child, grand‑parent ↔ grand‑child, etc.
- Collateral relations: involve a sibling step → aunt/uncle, niece/nephew, cousin.
- Same generation: siblings, cousins, or unrelated.
- Generation difference:
- 1 → parent/child
- 2 → grand‑parent/grand‑child
- 3 → great‑grand‑parent/great‑grand‑child
- Half‑relations: indicate only one common parent.
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Key terms: