Mendel’s Seven Pair of Contrasting Characters

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Mendel used Pea Plant and studied SEVEN pair of contrasting traits. Each character has one dominant trait and one recessive trait.

Character DOMINANT Trait Recessive trait
1 Seed Shape Round Wrinkled
2 Seed (Endosperm) Color Yellow Cotyledons Green Cotyledons
3 Seed Coat Color/ Flower Color Gray Coat

(Violet Flower)

White Coat

(White Flower)

4 Pod Color Green Yellow
5 Pod Shape Full/ Inflated Constricted
6 Flower Position/ Pod Position Axial Terminal
7 Plant Height/Stem Height/ Stem Length Tall Dwarf



Let’s consider, Tall (TT) plant is crossed with Dwarf (tt) plant, which produced Tall (Tt) plants as offspring.

In This example, Tall and Dwarf are phenotypes.

T & t are the Alleles.

‘T’ is a dominant allele while, ‘t’ is recessive allele.

Dominant allele is represented by capital letter, recessive with small letter.

TT, tt are genotypes.

‘T’ and ‘t’ are written as two letters  for Tall (TT) and Dwarf (tt), as one allele comes from both the parents.

  • Allele: Alternate forms of a gene, OR Different forms of the same gene. g. Dominant and recessive forms are called alleles. T or t
  • Genotype: Allelic constitution of each character is called its genotype OR It is the set of alleles that an individual organism possesses OR Genetic makeup of individual. TT, Tt, tt are all genotypes.
  • Phenotype: Individual’s observable traits or physical appearance of character, e.g. tall or dwarf characteristic is said as  Phenotype = genotype + environment, as phenotype is a result of genotype and individual’s interacting environment.
  • Locus: Specific place on a chromosome occupied by an allele. Different alleles for a particular gene occupy the same locus on homologous chromosomes.
  • Homozygous: Having two of the same allele. TT, tt, i.e both the alleles of same type.
  • Heterozygous: Having two different alleles. Tt , i.e both alleles of different type.
  • Dominant allele: An allele that produces its phenotype in heterozygous and homozygous form. TT produces Tall plants. Tt also produces Tall plant as ‘T’ allele is dominant over ‘t’ allele (which is recessive).
  • Recessive allele: An allele that produces its phenotype only in homozygous form. E.g. dwarf plants are produced only when genotype ‘tt’ is present.
  • Pure line Individuals of the same phenotype when crossed, always produce offspring with the same phenotype.
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