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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

SEX INHERITANCE Genes on the X and Y chromosomes

Human ChromosomesHuman Chromosomes: : 2 Sex 2 Sex ChromosomesChromosomes

Human ChromosomesHuman Chromosomes::44 Autosomes44 Autosomes

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

X-l inked InheritanceT. 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 .  

Examples of X-linked traits:1. Color Blindness2. Hemophilia3. Muscular Dystrophy4. Icthyosis simplex (scaly skin)

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.

ColorblindnessRED-GREEN

COLORBLINDNESS:

People with red-green color blindness see either a three or nothing at all.

Those with normal color vision see an 8.

Hemophilia

Hemophilia- Lacking in the ability to clot bloodThere 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.

Muscular Dystrophy

- Results in weakening/loss of muscles

- Caused by defective version of gene that codes for muscle

Sex-influenced TraitsSex-Influenced traits are those that are on autosomes, but occur

because of the sex hormones in male and female bodies.

Examples: Facial hair Baldness

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

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.

Quantitative charactersQuantitative characters are those showing countinuos

variation and which can be measured easily. Eg. yield ,plant hieght

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.

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.

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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.

Wheat kernel ColorTrue-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.

Additive

When the combined effects of alleles at different loci are equal to the sum of their individual effects

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

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.

EpistasisEpistasis 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

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

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