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Dominant and Recessive Traits - Definition, Homozygous Heterozygous Examples in Plants, Animals and Humans

Introduction to Alleles

There are 23 pairs of chromosomes in each human cell and hundreds of thousands of distinct genes on each chromosome.

  • An individual inherits two versions of each gene, known as alleles, from each parent.
  • An allele is a chromosomal pair of genes that controls a heritable trait.
  • Alleles categorized as dominant or recessive - dominant is visible trait, recessive not visible morphologically.
  • Dominant alleles denoted by capital letters, recessive by lowercase letters.
  • Homozygous trait has either two capital letters or two lowercase letters.
  • Heterozygous traits have alternating letters - capital letter always comes first in heterozygous alleles.

Example: Eye Color

  • Dominant gene for brown eyes B and recessive gene b for blue eyes.
  • Alleles for dominant trait can be BB or Bb while bb is for recessive trait.
  • Person exhibits dominant trait if they have heterozygous set BB or Bb.
  • Recessive trait requires both recessive alleles present bb - same alleles.
  • Having same two copies of allele is homozygous condition.
  • When only one copy present, recessive allele does not result in any trait.
  • Dominant trait can be expressed when one of two alleles is present.
  • Many genes interact in production of one trait like hair color, eye color, size, shape - one gene often influences many traits.

Dominant and Recessive Traits in Plants

Name of Plant Dominant Trait Recessive Trait
Nettle Serrated leaves Smooth margined leaves
Sunflower Branched habit Unbranched habit
Cotton Colored lint White lint
Maize Round starchy kernel Wrinkled sugary kernel
Snapdragon Red flower Non-red flower
Barley Beardlessness Beardness
Wheat Susceptibility to rust Immunity to rust
Tomato Two-celled fruits Many-celled fruit

Dominant and Recessive Traits in Animals

Name of Animal Body character Dominant Trait Recessive Trait
Cat Skin color Tabby Black or Blue
Cat Length of hair Short hair Long Hair
Dog Skin color Grey Black
Dog Tail Stumpy Normal
Cattle Face Color White Colored
Cattle Horn Poled or Hornless Horned
Horse Skin color Black Red
Horse Movement Trotting Pacing
Sheep Hair/Wool/Fleece White Black
Swine Skin color Black Red
Swine Hoof Uncleft Normal
Salamander Body color Dark light
Drosophila Eye color Red White
Drosophila Wings Flat and yellow Curled and White
Drosophila Body color Grey Black
Land snail Shape of shell Unbanded shell Banded shell

Dominant and Recessive Traits in Humans

Traits Dominant Recessive
Baldness (In male) Presence Absence
Body Hair Abundant Little
Bend Pinkie Finger Able to bend Not able to bend
Cleft in Chin Presence Absence
Crossing of Thumbs Left thumb over right thumb Right thumb over left thumb
Dimples Presence Absence
Earlobes Free earlobes Attached earlobes
Freckles Presence Absence
Iris Brown Blue
Hairline Widow's peak Straight
Hair Color Dark Light
Handedness Right handedness Left handedness
Hitchhiker's Thumbs Absence Presence
Lips width Broad lips Thin lips
Mongolian Eye Fold Presence Absence
Nose Shape Roman nose (bump) Straight
Nose Width Broad nose Narrow nose
Rh factor in Blood Rh positive (+) Rh negative (-)
Toe Length Second toe longer than first First toe longer than second
Tongue Rolling Ability to roll tongue Inability to roll tongue
Webbed Fingers Presence Absence

References

  • Altenburg E. (1965). The Relation of Genes to Traits. In Genetics (Revised Edition). Holt, Rinehart and Winston, Inc.
  • Biologywise. (2022). Dominant and Recessive Traits in Humans.
  • National Human Genome Research Institute (NIH). (2022). Recessive Traits and Alleles.
  • Verma P.S. and Agarwal V.K. (2005). Mendel and His work. In Cell Biology, Genetics, Molecular Biology, Evolution and Ecology. S. Chand & Company Ltd.

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