Genetics

• Genetics word first used by => W. Watson (in 1905).
• Transmission of character from one generation to next generation is called Heredity.
• The process of transfer of hereditary character from generation to generation called as Genetics.
• The characteristics which transmit from generation to generation is transported by Gene.

Gene: Gene word first coined by => W. Johannsen (in 1909). It is a unit of hereditary material located on chromosome. Gene itself or with other gene determine character of organism. Gene exist in number of alternative forms termed as alleles. Gene occasionally undergo for radial changes called as Mutation. The modern concept of perception about the gene was given by => Benjer (in 1956). Functional unit of gene => Cistron Unit of gene responsible for mutation => Muton Unit of gene take a part in recombination => Recon In Human 35000 gene are present.

• Gregor Johann Mendel said that hereditary character is transfer by gene.
• Hence Gregor Johann Mendel is known as Father of Genetics.

Mendel's Experiment:

• Mendel chooses 7 pair of pea plant species for his experiment.

 

Characters	Dominant characters	Recessive characters
Shape of the seed.	Spherical smooth seed.	Wrinkled seed.
Color of the cotyledon.	Yellow	Green
Color of flower.	Red	White
Shape of the fruit.	Smooth	Shrinked
Color of the fruit.	Green	Yellow
Position of the flower.	Tall	Farthest
Length or Height of the plant.	Tall	Dwarf

Mono-hybrid Cross:

Mendel made cross between 2 pure plant having contracting character for single trait called Mono-hybrid cross (i.e. Tall & Dwarf plant for height)

 

Phenotype ratio => 3 : 1

Genotype ratio => 1 : 2 : 1

Di-hybrid Cross:

Mendel made cross between 2 pure plant having in 2 pair of contracting character i.e. color & shape of seed called Di-hybrid cross. (i.e. Plant having round seed with yellow color & wrinkle seed with green color.)

 

Phenotype ratio => 9 : 3 : 3 : 1

Genotype ratio => 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1

 

Mendel's Law of Heredity:

• On the basis of mono-hybrid and Di-hybrid cross Mendel proposed law of heredity.

1. Mendel's First Law: (Law of dominance)

• According to it when two dissimilar unit factors are present in an individual only one is able to express.
• One that express itself is dominant character while which fail to express is recessive character.
• In the first generation only the dominant character is visible, while the recessive character is hidden and it appears in the next generation.

 

2. Mendel's Second Law: (Law of segregation)

•  According to this law during the gametes formation both the character which governed by gene is segregated and out of these factors only one factor is reached in the gamete.
• Both factors never come at a time in the gamete.
• This law is also called the Law of purity of Gametes.

3. Mendel's Third Law: (Law of Independent Assortment)

•  According to this law various pairs of the factors which exist in organism are independent to each other.
• Thus organism of new appearance may born.

 

Terms Related to Genetics:

1. Phenotype:
• The characteristics of the organism which are directly & visibly appreciable is called Phenotype.
2.  Genotype:
• The characteristics of the organism which are not directly & visibly appreciable is called Genotype.
3. Alleles:
• The genes which are represented in diversified form but which exhibit the same character are called alleles of the other.
4. Homozygous:
• If the pair of gene exhibits same character during cross pollination then it is called Homozygous.
• Eg. Tall plant (TT) & Dwarf plant (tt)
5. Heterozygous:
• If the pair of gene exhibits different character, in which one is dominant another is recessive the such pair is called heterozygous.
• Eg. Tall narrow plant (Tt)

 

 

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