Human Mendelian Traits

Dominant vs. Recessive Patterns & Cross Examples

BY PROF. SIDDHARTH SANGHVI SIR

1. Trait Overview Table

# Trait Character Dominant Phenotype (Symbol) Recessive Phenotype (Symbol)
1Hair TextureCurly Hair (H)Straight Hair (h)
2Eye ColorBrown Eyes (B)Blue Eyes (b)
3Earlobe AttachmentFree Earlobes (E)Attached Earlobes (e)
4Tongue RollingRoller (R)Non-roller (r)
5Cheek DimplesDimples (D)No Dimples (d)
6Thumb AngleStraight Thumb (S)Hitchhiker's Thumb (s)
7FrecklesHas Freckles (F)No Freckles (f)
8HairlineWidow's Peak (W)Straight Hairline (w)
9Finger NumberPolydactyly / 6 Fingers (P)Normal / 5 Fingers (p)
10PTC TasterTaster (T)Non-taster (t)

2. Detailed Cross Examples

Hair Texture 1

Dom: Curly (H) Rec: Straight (h)
Scenario: Heterozygous (Hh) × Recessive (hh).
× h h
H Hh Hh
h hh hh
Results:
  • 50% Curly (Hh)
  • 50% Straight (hh)

Eye Color 2

Dom: Brown (B) Rec: Blue (b)
Scenario: Heterozygous (Bb) × Heterozygous (Bb).
× B b
B BB Bb
b Bb bb
Results:
  • 75% Brown (BB, Bb)
  • 25% Blue (bb)

Earlobes 3

Dom: Free (E) Rec: Attached (e)
Scenario: Homo. Dom (EE) × Recessive (ee).
× e e
E Ee Ee
E Ee Ee
Results:
  • 100% Free Earlobes
  • All offspring are Carriers (Ee).

Tongue Rolling 4

Dom: Roller (R) Rec: Non (r)
Scenario: Heterozygous (Rr) × Recessive (rr).
× r r
R Rr Rr
r rr rr
Results:
  • 1 Roller : 1 Non-roller
  • 50% chance for each.

Cheek Dimples 5

Dom: Dimples (D) Rec: None (d)
Scenario: Heterozygous (Dd) × Heterozygous (Dd).
× D d
D DD Dd
d Dd dd
Results:
  • 3 Dimples : 1 No Dimples
  • 25% DD, 50% Dd, 25% dd.

Thumb Angle 6

Dom: Straight (S) Rec: Hitchhiker (s)
Scenario: Homo. Dom (SS) × Heterozygous (Ss).
× S s
S SS Ss
S SS Ss
Results:
  • 100% Straight Thumb
  • Genotypes: 50% SS, 50% Ss.

Freckles 7

Dom: Freckles (F) Rec: None (f)
Scenario: Heterozygous (Ff) × Recessive (ff).
× f f
F Ff Ff
f ff ff
Results:
  • 50% Freckles (Ff)
  • 50% No Freckles (ff)

Widow's Peak 8

Dom: Peak (W) Rec: Straight (w)
Scenario: Heterozygous (Ww) × Heterozygous (Ww).
× W w
W WW Ww
w Ww ww
Results:
  • 75% Widow's Peak
  • 25% Straight Hairline

Finger Number 9

Dom: 6 Fingers (P) Rec: 5 Fingers (p)
Scenario: Recessive (pp) × Recessive (pp).
× p p
p pp pp
p pp pp
Results:
  • 100% 5 Fingers
  • (Note: 5 fingers is recessive, but most common).

PTC Taster 10

Dom: Taster (T) Rec: Non (t)
Scenario: Heterozygous (Tt) × Heterozygous (Tt).
× T t
T TT Tt
t Tt tt
Results:
  • 3 Tasters : 1 Non-taster
  • 75% chance to taste bitterness.