Category: Biology Second Paper

Animals that produce the same type of gametes are called homogametic sex. Female members are the homogametic sex. Their gametes are called homogametes.

The chromosomes that determine the sex of an organism are called sex chromosomes. The 23rd chromosome in the human body is the sex chromosome. The two sex chromosomes are X and Y. It is called heterosome. A chromosome that does not play any role in determining the sex of an organism is called an autosome. Human body has 22 pairs of autosomes. Autosomes are identical XX. External differences are seen in male and female animals. This is called sexual dimorphism.

1. Presence of chromosomes: Chromosomes are always present in cells. If a cell is deficient in chromosomes, new cells produced from that cell will be deficient in chromosomes.
2. Pairing of Homologous Chromosomes: Homologous chromosomes are paired. That is, one small chromosome is linked to another small chromosome.
3. Independent Distribution of Chromosome Pairs: Chromosomes are arranged in pairs in organisms. Pairing is done independently.
4. Qualitative differences between chromosome pairs: Each chromosome contains genes controlling different traits. One chromosome causes normal cell growth and the other causes abnormal cell growth.
5. Sex determination: The sex of an organism is determined by sex chromosomes or allosomes.
6. Restoration: Fertilization restores the chromosome number in diploid cells.
7. Physical Basis of Heredity: Hereditary factors or genes are located on chromosomes. Hence it is called the physical basis of heredity.

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