Blood Relations – Quick Study Notes
(For the Lakshadweep Police SI Reasoning Ability Test)
1. What Are Blood Relations?
- People who share a common ancestor (parent, grand‑parent, great‑grand‑parent, etc.).
- No marriage or adoption is involved – only the family tree that comes from parents.
2. The Family Tree “Ladder”
- Up a rung = parent (father or mother).
- Down a rung = child.
- Same rung = sibling (brother / sister).
- Up → Down = aunt/uncle or niece/nephew.
- Up → Up → Down = cousin, and so on.
Think of it like a ladder that goes up to your grandparents, down to your kids, and sideways to your cousins.
3. Quick Rules (No Jargon)
| Step Up | Step Down | Relationship |
|---|---|---|
| 1 | 0 | Parent |
| 0 | 1 | Child |
| 0 | 0 | Self |
| 1 | 1 | Sibling |
| 1 → 1 | Aunt/Uncle (if you went up 1, then down 1) | |
| 1 → 1 | Niece/Nephew (if you went down 1, then up 1) | |
| 1 → 2 | Cousin (you go up 1 to grand‑parent, then down 2 to cousin) | |
| 2 → 1 | Cousin (you go up 2 to great‑grand‑parent, then down 1) | |
| 2 → 2 | First cousin once removed (up 2, down 2) |
- “Once removed” simply means one generation apart (e.g., your cousin’s child is your first cousin once removed).
4. How to Find a Relationship – 3 Easy Steps
- Start with one person – say A.
- Move up to the lowest common ancestor you both share.
- Count the steps up and down for each person.
- Match the numbers to the table above.
5. Tiny Example
Family Tree (ASCII)
Grandfather
/ \
Father Aunt
| |
A (you) B
|
C
- You (A) are the child of the Father.
- C is the child of B (your Aunt).
Find the relation between You (A) and C.
Steps
- Go up from A to Father (1 step).
- Go up from C to B to Father (2 steps).
- Lowest common ancestor = Father.
Counts
- A: 1 step up, 0 down.
- C: 2 steps up, 0 down.
Since one person is up 1 and the other up 2, they are First Cousins (up 1 → up 2 = cousin).
Answer: A and C are first cousins.
6. Quick Practice Problem
Problem
Mark is the son of Lisa. Lisa is the sister of Paul.
What is Mark’s relation to Paul?
Solution
- Mark → up 1 → Lisa.
- Paul → up 0 (he is Lisa’s sister).
- Common ancestor = Lisa’s parents (not needed here).
- Mark is Lisa’s son, Paul is Lisa’s sister.
- Up 1 + Up 0 = Uncle / Aunt?
Actually, Mark is Paul’s nephew (because Mark is the son of Paul’s sister).
Answer: Mark is Paul’s nephew.
7. Quick Tips
- Always start at the same person (e.g., the one whose relationship you’re asked to find).
- Count steps, not names – numbers are the key.
- Remember the ladder:
- 1 up = parent
- 1 down = child
- 1 up + 1 down = aunt/uncle or niece/nephew
- 1 up + 2 down = cousin
- 2 up + 1 down = cousin
- Remove = one generation difference (once, twice, etc.).
8. Cheat Sheet (Remember While Solving)
| Up | Down | Relation | Example |
|---|---|---|---|
| 1 | 0 | Parent | Child → up 1 |
| 0 | 1 | Child | Parent → down 1 |
| 0 | 0 | Self | — |
| 1 | 1 | Sibling | Brother/Sister |
| 1 | 2 | Cousin | Up 1, down 2 |
| 2 | 1 | Cousin | Up 2, down 1 |
| 1 | 3 | First cousin once removed | Up 1, down 3 |
| 3 | 1 | First cousin once removed | Up 3, down 1 |