Category: Biology Second Paper

Double recessive epistasis occurs when a recessive gene located at one locus on a chromosome inhibits the expression of a non-allelic recessive gene located at another locus. Due to latent epistasis the ratio of the second law of Mendelian inheritance is 9 : 7 instead of 9 : 3 : 3 : 1.

Crossing a White Leghorn (CCII) chicken with another White Wyndot (ccii) chicken produces a white chicken in the F1 line. Self-fertilization of white (CcIi) chickens in the F1 progeny resulted in 13 white and 3 colored chickens in the F2 progeny.
here,
White Leghorn chicken genotype CCII
White Wyndot chicken genotype ccii
The first progeny is F1 and the second progeny is F2
Parents : ♂ × ♀
Phenotype: White Leghorn White Wyndot
Genotype: CCII ccii
Gamete : (CI) (ci)
F1 Generation: CcIi (White)

Self fertilization : F1×F1
Parents : ♂ × ♀
Phenotype: White White
Genotype : CcIi CcIi
Gamete : (CI)(Ci)(cI)(ci) (CI)(Ci)(cI)(ci)
F2 Generation (checker board)
Comment: It can be seen from the checker board, out of 16 chickens, 13 are white and 3 are colored chickens. In this case the expressed gene I non-allele inhibits expression of the expressed gene C.
Phenotypic ratio : White : Colored = 13 : 3

Crossing a White Leghorn (CCII) chicken with another White Wyndot (ccii) chicken produces a white chicken in the F1 line. Self-fertilization of white (CcIi) chickens in the F1 generation resulted in 13 white and 3 colored chickens in the F2 generation.
here,
White Leghorn chicken genotype CCII
White Wyndot chicken genotype ccii
The first progeny is F1 and the second progeny is F2
Parents : ♂ × ♀
Phenotype: White Leghorn White Wyndot
Genotype: CCII ccii
Gamete : (CI) (ci)
F1 Generation : CcIi (White)

Svanishek : F1×F1
Parents : ♂ × ♀
Phenotype: White White
Genotype : CcIi CcIi
Gamete : (CI)(Ci)(cI)(ci) (CI)(Ci)(cI)(ci)
F2 generation (checker board)
Comment: It can be seen from the checker board, out of 16 chickens, 13 are white and 3 are colored chickens. In this case the expressed gene I non-allele inhibits expression of the expressed gene C.
Phenotypic ratio : White : Colored = 13 : 3

Crossing a White Leghorn (CCII) chicken with another White Wyndot (ccii) chicken produces a white chicken in the F1 line. Self-fertilization of white (CcIi) chickens in the F1 progeny resulted in 13 white and 3 colored chickens in the F2 progeny.
here,
White Leghorn chicken genotype CCII
White Wyndot chicken genotype ccii
The first progeny is F1 and the second progeny is F2
Parents : ♂ × ♀
Phenotype: White Leghorn White Wyndot
Genotype: CCII ccii
Gamit : (CI) (ci)
R1 lineage: CcIi (White)

Svanishek : F1×F1
Parents : ♂ × ♀
Phenotype: White White
Genotype : CcIi CcIi
Gamit : (CI)(Ci)(cI)(ci) (CI)(Ci)(cI)(ci)
F2 progeny (checker board)
Comment: It can be seen from the checker board, out of 16 chickens, 13 are white and 3 are colored chickens. In this case the expressed gene I non-allele inhibits expression of the expressed gene C.
Phenotypic ratio : White : Colored = 13 : 3

Expressed epistasis occurs when an expressed gene at one locus on a chromosome interferes with the expression of a non-allelic expressed gene at another locus. Leghorn, Wyndot, Plymouth Rocks, etc., feather colors are the result of pronounced epistasis. Bateson I Punnett (1908) noted this.

Due to pronounced epistasis, the ratio of Mendel’s second law of inheritance is 13 : 3 instead of 9 : 3 : 3 : 1.

A gene that inhibits the expression of an organism’s trait is called an epistatic gene. A gene that inhibits expression of a trait is called a hypostatic gene.

Epistasis is when a gene located at one locus on a chromosome interferes with the expression of a non-allelic gene located at another locus. Epistasis is of two types.  Apparent epistasis and Latent epistasis.

Crossing a sweet pea with a white flower (AAbb) with another white flower (aaBB) resulted in an F1 line with purple flowers (AaBb). Self-fertilization between purple (AaBb) flowers in the F1 progeny resulted in 9 purple and 7 white flowers in the F2 progeny.

here,

The first white flower genotype is AAbb

The second white flower genotype is aaBB

The first progeny is F1 and the second progeny is F2

Parents : ♂ × ♀

Phenotype: White flowers White flowers

Genotype : AAbb aaBB

Gamit : (Ab) (aB)

F1 Lineage : AaBb (Purple)

 

Self fertilization : F1×F1

Parents : ♂ × ♀

Phenotype: Purple flowers Purple flowers

Genotype : AaBb AaBb

Gamit : (AB)(Ab)(aB)(ab) (AB)(Ab)(aB) (ab)

F2 progeny (checker board)

Comment: From the checker board, out of 16 flowers, 9 are purple and 7 are white. The purple color of the flower is due to the combined effect of expressed genes A and B.

Phenotypic ratio : Purple : White = 9 : 7

If the combined effect of two genes is required for the manifestation of a characteristic of the organism, the two genes are called complementary genes.

 

A cross of a red (AA) cow with another white (BB) cow results in an F1 breed of rowan (AB) cows. Self-insemination of F1 rowan (AB) cows resulted in 1 red, 2 rowan and 1 white cow in R2.

here,

The gene responsible for red color is A

Genotype AA in red

again,

The gene responsible for white color is B

Genotype BB is white

The first progeny is F1 and the second progeny is F2

 

Parents : ♂ × ♀

Phenotype: Red and white

Genotype : AA BB

Gamit : (A) (B)

F1 Breed : AB (Rowan)

 

Self fertilization : F1×F1

Parents : ♂ × ♀

Phenotype: Rowan Rowan

Genotype : AB AB

Gamit : (A) (B) (A) (B)

F2 progeny (checker board)

Comment: It can be seen from the checker board, out of 4 cows, 1 is red, 2 is rowan and 1 is white.

Phenotypic ratio : Red : Rowan : White = 1:2:1