Dominant and Recessive Traits in Humans, Animals, and Plants

Table of Contents

• Introduction to Dominant and Recessive Traits
• Dominant and Recessive Traits in Plants
• Dominant and Recessive Traits in Animals
• Dominant and Recessive Traits in Humans
• References

Introduction to Dominant and Recessive Traits

• Humans have 23 pairs of chromosomes in each cell, with hundreds of thousands of distinct genes on each chromosome.
• Each individual inherits two versions of every gene, called alleles, from each parent.
• An allele is a chromosomal pair of genes responsible for controlling a heritable trait.
• Alleles can be classified as dominant or recessive.
• Dominant alleles represent traits that are visibly expressed, while recessive alleles correspond to traits that are not morphologically visible.
• Dominant alleles are typically represented by capital letters, and recessive alleles by lowercase letters.
• A homozygous trait consists of either two capital letters (dominant) or two lowercase letters (recessive).
• Heterozygous traits consist of one dominant and one recessive allele, with the capital letter (dominant allele) written first.
• For example, if "B" is the dominant allele for brown eyes and "b" is the recessive allele for blue eyes, then "BB" and "Bb" will express the dominant brown eye trait, while "bb" will express the recessive blue eye trait.
• A person will display the dominant trait if their alleles are either "BB" or "Bb" (homozygous dominant or heterozygous).
• To express a recessive trait, both alleles must be recessive (bb), meaning the individual is homozygous for the recessive gene.
• A homozygous condition involves having two identical copies of an allele.
• A single copy of a recessive allele does not produce the associated trait.
• A dominant allele can express the trait even if only one copy is present.
• Many traits, such as hair color, eye color, size, and shape, are influenced by the interaction of multiple genes.
• One gene can also influence many different traits, often in conjunction with other genes.

Dominant and Recessive Traits in Plants

In plants, several observable traits are determined by dominant and recessive alleles:

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 fruits

Dominant and Recessive Traits in Animals

In animals, dominant and recessive traits also vary across species and characteristics:

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

In humans, various physical traits are influenced by dominant and recessive alleles:

Trait	Dominant	Recessive
Baldness (in males)	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	Right thumb over left
Dimples	Presence	Absence
Earlobes	Free earlobes	Attached earlobes
Freckles	Presence	Absence
Iris color	Brown	Blue
Hairline	Widow’s peak	Straight
Hair color	Dark	Light
Handedness	Right-handed	Left-handed
Hitchhiker’s thumbs	Absence	Presence
Lip 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	First toe longer
Tongue rolling	Ability to roll	Inability
Webbed fingers	Presence	Absence

References

• Altenburg, E. (1965). The Relation of Genes to Traits. In Genetics (Revised Edition, p. 16). Holt, Rinehart and Winston, Inc.
• BiologyWise. (2022). Dominant and Recessive Traits in Humans. Retrieved September 13, 2022, from https://biologywise.com/dominant-recessive-traits-in-humans
• Classroom Partners. (2022). Punnett Square. Retrieved September 13, 2022, from https://pressbooks.umn.edu/classroompartners/chapter/punnett-squares/
• National Human Genome Research Institute (NIH). (2022). Recessive Traits and Alleles. Retrieved September 13, 2022, from https://www.genome.gov/genetics-glossary/Recessive-Traits-Alleles
• Verma, P.S., & Agarwal, V.K. (2005). Mendel and His Work. In Cell Biology, Genetics, Molecular Biology, Evolution and Ecology (Multi-color Edition, pp. 29–30). S. Chand & Company Ltd., Ram Nagar, New Delhi.