Genic interactions

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Genic interactions: Effect of one allele(or gene) on the other allele(or gene) of the same or different gene pair.It have two types:

***Allelic interaction: The alleles of the same gene is interact in such a way that it produce a new character.Also called Intraallelic/  Intragenic interaction.Examples:

Complete dominance    :  3 :1

Codominance                 :  1:2:1

Incomplete dominance :  1:2:1

Link of all type of dominance

***Inter-allelic interaction: Two or more genes interacts and affect the expression of each other.Also called intergenic/non-allelic interaction.Examples:

All epistasis

Supplementary genes:  9: 3: 4

Collabarative gene effect : 9: 3 : 3 : 1

Inhibitory gene    : 13 : 3

Polymeric gene   : 9 : 6 :1

***Mendel monohybrid ratio :      3: 1

Mendel dihybrid phenotypic ratio: 9: 3: 3: 1

All gene interactions are modification of this ratio.

***Epistasis: When one gene hide or masks the effect of another gene,this phenomenon is called epistasis.

Epistasis gene: Gene which mask the effect of other gene is called epistasis gene.

Hypostasis gene: Gene whose effect is masked by other gene is callef hypostasis gene.

Types:

1)Dominant epistasis :   12: 3 :1

2)Double dominant epistasis/Duplicate genes:  15: 1

3)Recessive epistasis9: 3: 4

4)Double recessive epistasis/Complementary genes :  9: 7

Trick:  In case of double  ; in dominant first 2 ratio added and in recessive lastvtwo ratio added.

        .............Dominant epistasis............

When dominant  allele of a gene pair in homozygous as well as in heterozygous condition mask the effect of dominant allele of other gene pair.Example:

FRUIT COLOUR IN SUMMER SQUASH

W - white coloured

Y -Yellow  coloured(in complete absence ofW)

y and w- green coloured

.Double dominant epistasis/Duplicate genes..

When dominant alleles of two different gene pairs interact in such a way that any one of them can produce a particular effect even when present alone.Example:

POD SHAPE IN SHEPHERD PURSE

C -triangular shape

D- triangular shape

c and d -oval shaped

Capsella -bursa-pestoris(Shepherd purse)

       ...........Recessive epistasis..............

When recessive allele of a gene pair in homozygous condition mask the effect of dominant allele of another gene,then it is called recessive epistasis.Example-

COAT COLOUR IN MICE

effect of A -agouti colour

effect of C -black colour but in complete absencr of dominant A

****recessive homozygous cc mask effect of dominant A.Example- Aacc give albino ;agouti effect of A is masked due to homozygous cc.

***C is apparently supplementary for A

pic source:google

               Double recessive epistasis /                              Complementary  genes

When two genes present on different loci interact together  in such a way that dominant alleles of both are necessary for the expression of a particular phenotype.Example:

FLOWER COLOUR IN Lathyrus odoratus (discovered by Bateson and Punnette.

SEED COLOUR IN MAIZE

W -alone non-functional

Y- alone non-functional

W,Y both dominant gene together produce colour 

              .......Inhibitory genes......

One dominant gene prevents the expression of  other dominant gene.

IC both dominant inhibit the effect of each other and have white colour

ic-white (recessive)

one recessive homozygous,other dominant cause colour.

 

            .......Supplementary genes........

In case of supplementary genes,the gene produces its effect independently but the dominant allele of the another gene pair gives it expression only in absence of dominant allele of other gene which is supplementary for it.Example: SEED COLOUR IN Lablab

K -khakhi colour

k -buff colour in homozygous

L-chochlate colour in presence of K

K-functional alone

L- non functional alone;functional only in presence of dominant allele of K

Phenotypic  ratio: 

Chochlate :Buff :  khakhi

9                 :   3   :     4