Genetics 24231
Download
1 / 13

Genetics 24231 Faculty of Agriculture - PowerPoint PPT Presentation


  • 186 Views
  • Uploaded on

Genetics 24231 Faculty of Agriculture. Instructor: Dr. Jihad Abdallah Topic 12: Introduction to Quantitative Genetics. Simply Inherited and Polygenic Traits. Simply inherited traits: traits affected by one or few genes (coat color, presence of horns, shape of seed in garden pea, …..).

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Genetics 24231 Faculty of Agriculture' - freja


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Slide1 l.jpg

Genetics 24231Faculty of Agriculture

Instructor: Dr. Jihad Abdallah

Topic 12: Introduction to Quantitative Genetics


Slide2 l.jpg

Simply Inherited and Polygenic Traits

  • Simply inherited traits: traits affected by one or few genes (coat color, presence of horns, shape of seed in garden pea, …..).

  • Phenotypes of simply inherited traits are placed into categories (qualitative or categorical or discontinuous traits)

  • Not affected or very little affected by the environment.


Slide3 l.jpg

  • Polygenic traits: are traits affected by many genes (no single gene having an overriding effect) like growth rate, milk production, birth weight, etc.

  • Generally described in numbers.

  • Typically quantitative or continuous in their expression (quantitative or continuous traits)

  • Polygenic traits are affected by the environment.

  • They generally have a normal distribution


Slide4 l.jpg


Slide5 l.jpg

  • Quantitative genetics: affect quantitative traits are called is the science which deals with the inheritance of quantitative traits.


The basic model for quantitative traits l.jpg
The basic model for quantitative traits affect quantitative traits are called

  • P = G + E

  • P = phenotypic value for the trait of one individual (plant or animal).

  • G = the effect of the genes carried by the individual (genotypic value).

  • E = the effect of the environmental factors on the phenotype of the animal.


Genotypic value l.jpg
Genotypic Value affect quantitative traits are called

  • Genotypic value is the overall effect of all the genes carried by the individual on its phenotype. It includes:

  • Additive effects of genes (A): the sum of individual effects (average effects) of alleles.

  • Dominance effects of genes (D): interaction between alleles at the same gene

  • Epistatic effects (I): interaction between alleles on different genes

  • G = A + D + I P = A+ D + I + E


The phenotypic variance is decomposed into genetic and environmental variances l.jpg
The phenotypic variance is decomposed into genetic and environmental variances

  • VP = VA + VD + VI + VE

  • VP = phenotypic variance (total variance)

  • VA = the variance due to additive effects of genes

  • VD = the variance due to dominance effects of genes

  • VI = the variance due to epistatic effects of genes

  • VE = the variance due to environmental effects.


Slide9 l.jpg

Heritability environmental variances

  • Heritability in the broad sense (H2):is the proportion of the phenotypic variance that is due to all genetic effects ( additive, dominance and epistasis):

It measures the strength of the relationship between the phenotypic values of the individuals and their genotypic values.


Slide10 l.jpg

Heritability in the narrow sense ( environmental variancesh2):is the proportion of the phenotypic variance that is due to additive genetic effects only.

  • It measures two things:

  • The degree to which the offspring resemble their parents in the phenotype for a trait.

  • The strength of the relationship between the phenotypic values and the additive genetic effects (the relationship between P and A).


Slide11 l.jpg

  • Notes: environmental variances

  • Heritability is a measure on a population of individuals in a given environment for a given character. It is NOT measured on one individual.

  • Heritability can be estimated for each quantitative trait.

  • It varies from population to another and from environment to another for the same traits.


Importance of heritability l.jpg
Importance of heritability environmental variances

  • Heritability is very important in selection (in genetic improvement)

  • It determines if phenotypic selection would be efficient or not:

  • Small heritability: phenotypic selection is not efficient (low accuracy of selection).

  • High heritability: phenotypic selection is efficient (high accuracy of selection)


Example l.jpg
Example environmental variances

  • Suppose that for lamb weight at six months for the sheep population in Palestine: VA = 40, VD=8, VI =2, VE=50. Calculate the heritability in the broad sense and heritability in the narrow sense for this trait.

Heritability in the broad sense:

Heritability in the narrow sense:


ad