In 1902, American geneticist and German geneticist expressed chromosome theory. Genes that control the characteristics of organisms are located on chromosomes, during cell division the chromosomes divide and move to opposite poles and the genes separate. This is called the chromosomal theory of heredity.

A marriage of a Negro male (AABB) to a white (aabb) female results in mulatto offspring in the F1 lineage. Intermarriage between mulatto (AaBb) offspring in the F1 lineage resulted in F2 offspring with 1 Negro, 4 Dark, 6 Medium, 4 Light, and 1 White.

here,

Genotype of Negro male is AABB

The genotype of the white female is aabb

First progeny is F1 and second progeny is F2

 

Parents :             ♂        ×      ♀

Phenotype: Negro male     white female

Genotype :     AABB             aabb

Gamit :            (AB)              (ab)

F1 breed :                AaBb (mulatto)

 

Self fertilization : F1×F1

Parents :         ♂      ×       ♀

Phenotype: mulatto     mulatto

Genotype :    AaBb      AaBb

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

F2 progeny (checker board)

Remarks : From the checker board, out of 16 children, 1 is Negro, 4 are dark, 6 are medium, 4 are light and 1 is white. In this case, the skin color has become darker as the number of expressed genes increases.

Phenotypic Ratio : Negro : Dark : Medium : Light : White = 1:4:6:4:1

 

1. Phenotypic traits are controlled by two or more genes.
2. Its magnitude can be determined by measurement.
3. A great diversity of organisms is seen.
4. A, B and C are expressed states and a, b and c are secreted states.
5. The expression capacity of each expressed gene is equal. That is, A = B = C
6. The presence of each expressed gene (A or B or C) increases a person’s height by 3 inches.
7. Latent homozygous (aabbcc) males are 5 ft and homozygous (aabbcc) females are 4 ft  in tall.

Heritable phenotypic traits that are controlled by two or more genes and can be quantified are called polygenic inheritance or polygenic inheritance. Such inheritance does not follow Mendel’s law. If its dimensions are measured and presented in a diagram, it is bell shaped. Polygenes cause autism, cancer, diabetes type-2 etc. in humans.

When many genes located at different loci of a chromosome express the same trait together, it is called a polygene. Human height, complexion, weight, eye color, intelligence, behavior etc. are controlled by polygenes.

When many genes located at different loci of a chromosome express the same trait together, it is called a polygene. Human height, complexion, weight, eye color, intelligence, behavior etc. are controlled by polygenes.

 

Polygenic inheritance

Heritable phenotypic traits that are controlled by two or more genes and can be quantified are called polygenic inheritance or polygenic inheritance. Such inheritance does not follow Mendel’s law. If its dimensions are measured and presented in a diagram, it is bell shaped. Polygenes cause autism, cancer, diabetes type-2 etc. in humans.

 

Characteristics of polygenic inheritance

1. Phenotypic traits are controlled by two or more genes.
2. Its magnitude can be determined by measurement.
3. A great diversity of organisms is seen.
4. A, B and C are expressed states and a, b and c are secreted states.
5. The expression capacity of each expressed gene is equal. That is, A = B = C
6. The presence of each expressed gene (A or B or C) increases a person’s height by 3 inches.
7. Latent homozygous (aabbcc) males are 5 ft and homozygous (aabbcc) females are 4 ft 7 in tall.

 Explanation of polygenic inheritance

A marriage of a Negro male (AABB) to a white (aabb) female results in mulatto offspring in the F1 lineage. Intermarriage between mulatto (AaBb) offspring in the F1 lineage resulted in F2 offspring with 1 Negro, 4 Dark, 6 Medium, 4 Light, and 1 White.

here,

Genotype of Negro male is AABB

The genotype of the white female is aabb

First progeny is F1 and second progeny is F2

 

Parents :             ♂        ×      ♀

Phenotype: Negro male     white female

Genotype :     AABB             aabb

Gamit :            (AB)              (ab)

F1 breed :                AaBb (mulatto)

 

Self fertilization : F1×F1

Parents :         ♂      ×       ♀

Phenotype: mulatto     mulatto

Genotype :    AaBb      AaBb

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

F2 progeny (checker board)

Remarks : From the checker board, out of 16 children, 1 is Negro, 4 are dark, 6 are medium, 4 are light and 1 is white. In this case, the skin color has become darker as the number of expressed genes increases.

Phenotypic Ratio : Negro : Dark : Medium : Light : White = 1:4:6:4:1

Mating of a DDee male to a ddEE female results in an F1 offspring with normal speech and hearing. Intermarriage between normal speech hearing (DdEe) offspring in the F1 generation resulted in 9 normal speech hearing and 7 deaf offspring in the F2 generation.

here,

The genotype of the crowned male is DDee

Genotype ddEE of the crowned female

The first progeny is F1 and the second progeny is F2

 Parents : ♂ × ♀

Phenotype: crowned male  crowned female

Genotype :    DDee              ddEE

Gamete :           (De)                (dE)

F1 Lineage :          DdEe (Speech Hearing)

 

Self fertilization : F1×F1

Parents :                 ♂             ×              ♀

Phenotype : speech hearing      speech hearing

Genotype :         DdEe                      DdEe

Gamete : (DE)(De)(dE)(de)   (DE)(De)(dE)(de)

F2 progeny (checker board)

Comment: It can be seen from the checker board, out of 16 children, 9 are hearing and 7 are hearing impaired. In this case, if the recessive gene d or e is present in double form (dd/ee), the child will be born.

Phenotypic Ratio : Normal Speech Hearing : crowned = 9 : 7

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