This document discusses various modes of inheritance including sex-linked, sex-influenced, sex-limited, quantitative, and epistasis. It provides examples of X-linked traits like color blindness, hemophilia, and muscular dystrophy. It also describes quantitative inheritance being controlled by multiple genes and influenced by factors like dominance, additive effects, and epistasis. Quantitative trait loci are defined as the chromosomal positions where genes affecting quantitative traits are located.

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SUBMITTED BY :-
NARAIN DHAR
[M.Sc.(Ag) 1st
yr]
2016-17
SUBMITTED TO:_-
Dr.S.S.GAURAV
(Asso. Professor)
Dept- Genetics & Plant
Breeding

3. SEX INHERITANCE
Genes on the X and Y chromosomes

4. Human ChromosomesHuman Chromosomes:: 2 Sex2 Sex
ChromosomesChromosomes

5. Human ChromosomesHuman Chromosomes::
44 Autosomes44 Autosomes

6.  genes found on a sex chromosome
X-linked genes are genes found on the
X chromosome, symbolized by Xr
, XR
,
Y0
.
Y-linked genes are found on the Y
chromosome, symbolized by X0
, YR
, Yr

7. X-linked Inheritance
T. H. Morgan (1910) in his studies on inheritance of genes
in Drosophila discovered that the pattern of inheritance .the
first study of x- linked inheritance for eye gene colour in
drosophila.
White eyed female x Red eyed male
 Red eyed female x white eye in male .

9. Examples of X-linked traits:
1. Color Blindness
2. Hemophilia
3. Muscular Dystrophy
4. Icthyosis simplex (scaly skin)

10. Colorblindness
A person with normal color vision seen a number seven in
the circle above.
Those who are color blind usually do not see any number at
all.

11. Colorblindness
RED-GREEN
COLORBLINDNESS:
People with red-green
color blindness see either
a three or nothing at all.
Those with normal color
vision see an 8.

12. Hemophilia
Hemophilia- Lacking in the
ability to clot blood
There is a gene on the “X”
chromosome that control
blood clotting
People who have
hemophilia are missing the
protein to clot blood
They can bleed to death by
minor cut.

13. Muscular Dystrophy
- Results in
weakening/lo
ss of muscles
- Caused by
defective
version of
gene that
codes for
muscle

14. Sex-influenced Traits
Sex-Influenced traits are those that are on autosomes, but occur
because of the sex hormones in male and female bodies.
Examples: Facial hair
Baldness

15. Sex Limited
These are characters only expressed in one sex. They may be
caused by genes on either autosomal or sex chromosomes.
The traits limited to only one sex due toanatomical
diffirences are called a sex limited traits.
Examples:1.Female sterility in Drosophila 2.Gene for milk
production indairy cattle effected only cows

16. Quantitative Inheritance
A Quantitative inheritance it is controlled by many genes. Therefore,
it is known quantitative inheritance and also polygenic inheritance.
Quantitative traits = phenotypes differ in quantity rather than type
(such as height)
In a genetically heterogeneous population, genotypes are formed by
segregation and recombination.

17. Quantitative characters
Quantitative characters are those showing countinuos
variation and which can be measured easily.
Eg. yield ,plant hieght

18. MULTIPLE FACTER
HYPOTHESIS
Multiple facter hypothesis was originally postulated
by YULE in 1906. and multiple Gene model
Developed by geneticist .H.Nilsson
Ehle in 1910 explain 1.Inheritance of kernel colour
in wheat.

19. Multiple gene hypothesis:
range of phenotypes can be accounted for
by cumulative effect of many alleles.
Polygenes: Additive allele; nonadditive allele
1 phenotypic traits can be measured eg. weight or
height
2 two or more loci (genes) could account for
phenotype in an additive or cumulative way
3 each loci may be occupied by an additive allele,
which contributes a constant amount to the
phenotype, or a nonadditive allele which does not
4 The contribution by each allele
may be small and is approx equal
5 together the alleles contribute to a single
phenotypic character with substantial variation.

20. 2

21. An example: wheat kernel colour.
Cross true-breeding plants with white berries to
true-breeding plants with dark red berries.
The resultingF1 all exhibit an intermediate color.
When the F1s are crossed, the result is a range
of color.

22. Wheat kernel Color
True-breeding plants with white vs. red
berries were crossed to create an
F1of intermediate color, then the F1
plants were crossed to produce the
range of colors.
The curve is called a normal
distribution, with the largest
number of individuals in the
intermediate range, with fewer at
each extreme.

23. Additive
When the combined effects of
alleles at different loci are equal
to the sum of their individual
effects

24. Dominance
The phenomenon of F1 hybrid
being identical to one of its a
character is turmed as
dominance .
1.Incomplete dominance
2.complete dominance 3.co-
dominance

25. OVER DOMINANCE
In cases of some genes the intensity
of character governed by them is
greaterin heterozygotes than in two
concerned homozygotes this situation
is knows overdominance.
Example ABO blood group systems
in Humans.

26. Epistasis
Epistasis is an intraction between alleles at two
gene loci that affect a single trait which may
sometimes resemble a dominance intraction
between two diffirent alleles at the some locus
Epistasis modifies the characteristics 9:3:3:1 ratio

27. Quantitative Trait Loci(QTL)
 A Locus is that position in a chromosome at which a
gene is situated.
Thus a quantitative trait loci (QTL) is the chromosome site
at which a gene /group of genes affecting a quantitative is
located

28. THANK YOU