Dear students, in this ppt you will able to understand about the Incomplete dominance. Incomplete dominance is an allelic interaction. In incomplete dominance, both alleles of a character express their character in the F1 generation.

1. Incomplete Dominance
Dr. K. GANESH KUMARI
ASSISTANT PROFESSOR
DEPARTMENT OF BOTANY
SRIMAD ANDAVAN ARTS AND SCIENCE COLLEGE (AUTONOMOUS)
TRICHY - 5

2. Alleles or Allelomorphs
• A pair of genes controlling the same
character and located at the same
locus in the homologous
chromosomes are known as alleles or
allelomorphs.
• Eg. The gene content of the F1 plant is
Tt.
• These two genes are called alleles
because they are located in the same
locus of homologous chromosomes.
• So T is allelic to t or vice versa.

3. Cont…
• Each alternative of a character is controlled
by a gene.
• For example, tallness is controlled by a gene
T and its alternative characater dwarfness is
controlled by a gene t.
• The two genes (T and t) representing the two
alternatives (Tall and dwarf) of a particular
character (height) are present in two
separate chromosomes (homologous
chromosomes).
• These genes are located in the same locus on
the homologous chromosomes.
T t

4. Introduction
• Incomplete dominance is an allelic
interaction.
• In incomplete dominance, both
alleles of a character express their
character in the F1 generation.
• So the F1 individual has an
intermediate character between the
parents.
• Eg. Mirabilis jalapa (Four O’ Clock
plants)

5. Inheritance of flower colour in
Mirabilis
• When a homozygous red flowered (RR)
of 4 O’ clock plant (Mirabilis) is crossed
with a homozygous white flowered
plant (ww) a pink coloured variety is
produced (Rw)
• This is due to the incomplete
dominance of the gene R over its allele
w.
• The expression of the two genes (R
and w) in the same individual leads to
the production of an intermediate
character.

6. Cont…
• When F1 plants (Rw) are crossed, the
F2 plants are produced in the ratio 1
Red: 2 Pink: 1 White instead of the
Mendelian 1:3 ratio.
• It is a non – Mendelian ratio.
• Here the phenotypic and genotypic
ratios are the same; i.e. 1:2:1
• It is due to allelic interaction because
the pink colour is produced by the
interaction of two alleles located in
the same locus.

7. Inheritance of Flower colour
in Pea plant
• In the Pea plants (the same plant which
Mendel selected for his experiment) red
flower is dominant (RR) and white flower is
recessive (rr).
• When red flowered plant is crossed with a
white flowered plant, the F1 plants produce
pink flower (Rr).
• When F1 plants are crossed, they produce F2
plants in the ratio 1 Red: 2 Pink: 1 White.
• Thus the phenotypic ratio is 1:2:1 instead of
1:3 of Mendel.
• It is a non – Mendelian ratio.

8. Cont…
• Here the phenotypic and genotypic
ratios are same, that is 1:2:1.
• In pea plant R allele is incompletely
dominant over the recessive
alleles.
• The pink colour is produced by the
interaction of dominant and
recessive genes.
• It is an allelic interaction.
• It is a case of blending inheritance.

9. Feather colour in Fowl
• In Andulasian fowl, the black feather
(BB) is dominant and white feather
(bb) is recessive.
• When these two fowls are crossed,
the F1 offspring are blue coloured.
• When F1 fowls are crossed, the F2
generation individuals are formed in
the ratio 1 black, 2 blue and 1 white.
• Thus the phenotypic ratio is 1:2:1
instead of the 1:3 ratio of Mendel.

10. Cont…
• It is a non – mendelian ratio.
• Here the phenotypic and
genotypic rations are same, that
is 1:2:1
• In fowl, B allele is incompletely
dominant over b allele.
• The blue colour is produced by
the interaction of dominant and
recessive alleles.
• It is a case of blending
inheritance.

11. Inheritance of Glume in Wheat
• In wheat, elongated glume is controlled by the dominant gene EL and
short glume is controlled by the recessive gene el.
• The EL gene is incompletely dominant over el gene.
• Therefore, when a wheat plant with elongated glume is crossed with
another plant with short glume, the offspring will produce glumes of
intermediate lengths.

12. Inheritance of Maturity time
• Early maturity is controlled by incompletely dominant gene EM.
• When an early maturing plant (EM) is crossed with a late
maturing plant (em), the hybrids are intermediate in maturity
time.

13. Inheritance of Waxy Lemma
• Gene for waxy lemma (Wa) in Oats is incompletely dominant
over non – waxy lemma (wa).
Inheritance of Ragged Leaves
• Gene for ragged leaves (RG) in corn is incompletely dominant
over the gene for normal leaves (rg).

14. Thank you