This document presents information on quantitative traits in three paragraphs: 1) It introduces quantitative genetics and examples of quantitative traits in plants and humans. Quantitative traits show continuous variation and are influenced by multiple genes rather than a single gene. 2) It compares qualitative and quantitative traits, noting differences in variation, gene effects, analysis methods, and examples like wheat kernel color and human skin color. 3) It provides details on studies of wheat kernel color, human skin color, and human eye color to illustrate inheritance of quantitative traits controlled by multiple factors or polygenes. Genotypic ratios and phenotypic ratios are presented for each example.

1. Presented By…
Maitri. M. Thakor
M.Sc. (Botany)
Department of life sciences,
H.N.G.U., Patan.
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2.  Introduction
 Difference between qualitative &
quantitative traits
 The multiple factor Hypothesis
 Some characters of quantitative traits
☻Kernel colour in Wheat
☻Skin colour in human
☻Eye colour in human
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3.  Quantitative genetics have possibility of
continuous variations.
 In 1760, Joseph Kolreuter reported first
case of continuous variation due to
quantitative trait.
 Quantitative Characters are an inherited
character that expressed phenotypically in
all degrees of variation between one often
indefinite extreme and another : a
character determined by polygenes.
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4. Qualitative Trait Quantitative Traits
1)Characters of kind.
2)Discontinuous variation;
distinct phenotypic
classes.
3)Single gene effect.
4)Concerned with individual
matings & their progeny.
5)Analysed by making counts
and ratios.
1)Characters of degree.
2)Continuous variations;
phenotypic measure-
ments from a spectrum.
3)Polygenic control; effects
of single genes too slight
to be detected.
4)Concerned with population
of organisms consisting of
all possible kinds of
matings.
5) Statistical analyses.
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5. Qualitative Trait Quantitative Trait
(6) Ex.;
 Form (round/wrinkled
seeds of pea),
Structure ( horned /hornless
conditions in cattle’s)
Pigments (black/white coat
of guinea pigs)
Antigens & Antibodies
etc.
(6) Ex.;
In human ( Skin colour, Eye
colour, Hair colour, Weight,
Height etc.)
In plants (Seed colour in
Wheat, Ear size in Maize,
Corolla length in tobacco
etc.)
In animals (Size in chicken,
Size in Rabbit, White spotting
in mice etc.)
etc.
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6.  A gene, individually producing a slight
effect on the phenotype but in
combination with a few(2) or many other
genes, controls as quantitative character
is called as a Polygene.
 Since there are many genes of this kind
for one quantitative character, they are
also known as multiple factors, each
factor having too small an effect to be
traced.
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7.  Those genes(alleles) which contribute to
the trait involved are called Contributing ,
effective or active genes(alleles).
 Those genes(alleles) which do not
contribute to the trait involved are called
non- contributing, non-effective or null
genes(alleles).
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8.  The inheritance of relatively simpler
quantitative traits due to multiple factors
of polygenes will be illustrated in this
section with the help of three examples:
(1) Kernel colour in Wheat
(Studied by – H. Nilsson - Ehle )
(2) Skin colour in humans
(Studied by – C. B. Devenport )
(3) Eye colour in human
(Studied by – Burns & Battino-1989 )
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9.  A whole grain or seed of a cereal plant
such as corn, wheat, barley, etc.. Is called
Kernel.
 Kernel colour in wheat was studied by
Swedish geneticist H. Nilsson – Ehle for the
first time in 1908.
P : Red kernel White kernel
R1R1R2R2 (Dominant) r1r1r2r2 ( Recessive)
R1R2 r1r2
F1: R1r1R2r2 ( Light Red )
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10.  F2 Generation :
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11. Genotype Genotypic
ratio
Number of
Contributing
alleles
Phenotype Phenotypic
ratio
R1R1R2R2 1 4 Red 1
R1R1R2r2 2 3 Medium red
R1r1R2R2 2 3 Medium red
R1r1R2r2 4 2 Light red
R1R1r2r2 1 2 Light red
r1r1R2R2 1 2 Light red
R1r1r2r2 2 1 Very light
red
r1r1R2r2 2 1 Very light
red
r1r1r2r2 1 0 White 1
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12.  This character was given by Davenport
(1913) in Jamaica.
 He found that two pairs of genes, A-a and B-
b cause the differences in skin pigmenta-
tion between negro and Caucasian people.
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13. P1: Negro White
AABB aabb
AB ab
F1: AaBb
Mulattoes-
( intermediate skin colour )
F2 generation :
AB Ab aB ab
AB AABB AABb AaBB AaBb
Ab AABb Aabb AaBb Aabb
aB AaBB AaBb aaBB aaBb
ab AaBb Aabb aaBb aabb
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14. Phenotype Genotype Genotypic
Frequency
Ratio
Negro(Black) AABB 1 1
Dark AaBB 2
Mulatto AABb 2
Mulatto AaBb 4
Mulatto aaBB 1
Mulatto Aabb 1
Light Aabb 2
Light aaBb 2
White aabb 1 1
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15. 1 : 4 : 6 : 4 : 1
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16.  In human beings, the colour of eye is
found to be determined by Polygenes.
 This genes have been suggested to be X-
linked (see Burns and Battino, 1989).
 At least 9 classes of eye colour can be
recognized in humans.
 In order of increasing amount of melanin
pigmentation, these eye colours can be
designated as light blue, medium blue,
dark blue, grey, green, light brown,
medium brown and dark brown.
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17.  Number of contributing alleles for each type
of eye colour of human beings :
Number of
contributing alleles
Eye colour
0 Light blue
1 Medium blue
2 Dark blue
3 Grey
4 Green
5 Hazel
6 Light brown
7 Medium brown
8 Dark brown
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18. Different eye colours found in human beings.
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