GENETICS is the branch of science that deals with the study of heredity and variation.

HEREDITY is the transmission of characters traits from one generation to the next generation.

VARATION is the difference in the characters or traits between the parents and their next generation. Variation is sub classed into Somatic variation and Gametic variation.

SOMATIC VARATION takes place on body cell which are not inherited and also nor transmitted they are also called ACQUIRED TRAITS.  e.g. cutting of tails in dogs.

GAMETIC VARIATION that takes place in the gametes during reproduction, they are inherited as well as transmitted therefore known as inherited traits. e.g. height of a person, eye colour, skin colour.

VARATION DUE TO REPRODUCTION appears when the organism multiple itself either by asexually or sexually. In asexual reproduction variation found in very less proportion if that take place which is due to inaccuracies in DNA copying in Mutation. In sexual reproduction variation occurs in large quantity due to crossing over separation of chromosomes and mutation.

IMPORTANCE OF VARITION   It has been proved to be important it depends on the nature of variation of different individuals get different benefit such as thermostatic bacteria can survive in better wave in heat waves. The other main benefit that species can adapt itself with change in environment and their survival become possible.

GREGOR JOHANN MENDEL  1822- 1884 He  began his experiment on plant breeding and hybridization. He gave the Law of inheritance in living organism therefore called the FATHER of GENETICS.

PLANTS SELECTION He selected the garden pea known as Pisum Sativum he took number of contrast characters for his experiment. He took following characters.

Dominant Trait :  Seed Shape   Round,  Seed Colour   Yellow, Flower Colour   Violet, Pod Shape   Inflated/ full.

Recessive Traits  Seed  , Wrinkle Seed  Colour   Green ,  Flower Colour  White  Pod Shape constricted.

MENDEL’S EXPERIMENT: He chose garden pea for his experiment because the contrast traits of several characters were detectable, the life span of the plant is short, normally self-fertilization takes place in them, but cross fertilization was also possible large number of seeds can be produced.

Mendel conducted many experiments; he crossed the pollinated plants to study the one character at a time.

Mono Hybrid Cross: In this Cross made between the two pea plants with one pair of contrast characters is called monohybrid crossing for example cross between tall (dominant trait) and dwarf Recessive trait)

mono hybrid


mono hybrid


a) All F1 progeny were tall there was no one of medium height plants it is half way character

b) In F2 progeny 1/4 were short and 3/4 were tall

c) Phenotypic ratio  F2  3:1    3 were tall and  1 was short, in Genotypic ratio of F2 1:2:1 it means one is TT two Tt other is tt

CONCLUSIONS:  TT and Tt were the tall plants tt was the short plant, single copy of T is sufficient to make the plant taller whereas t copy to make plant short, T is dominant trait because it expresses itself t recessive because it remain suppress.

DIHYBRID CROSS It is the cross between the two plants having two contrast characters   Parent Generation Round Green (RRyy) and wrinkled yellow (rrYY) seeds were taken.




Phenotypic Ratio   Round 9 , Round Green  3  , wrinkle Yellow  3 , Wrinkle Green  1 (9:3:3:1)

OBSERVATIONS: When  RRyy   was crossed with   rrYY  in F1 generation all were RrYy were the round and yellow seeds. The self-pollination of F1 plants gave the parental phenotype and two mixture seed plants in ratio as mentioned above.

Conclusion: Round and Yellow were the dominant traits, the occurrence of new phenotype combinations shows that genes for the round and yellow seeds are inherited independently to each other

MENDEL’S LAW OF INHERITANCE: Mendel based on his experiments of hybridization experiments he proposed the laws of inheritance.

LAW OF DOMINANCE: When two alternative forms of traits or characters or genes are present in the organism only one factor expresses itself in F1 progeny it is called dominant trait while remain masked it is called recessive traits. Characters are controlled by discrete units called factors found in pairs.

LAW OF SEGREGATION or LAW OF PRUITY OF GAMETES This law states that the factors of alleles/ characters   of a pair segregate from each other during the gamete formation such that  a example receive only one of the factors They do not show any blending but simply remain together. Homozygous parent produces all gametes that are similar whereas Heterozygous parent produces two type of gametes each having one allele in equal proportion.

when two pairs of characters /traits are combined together in hybrid segregation of one pair of character is independent of the other pair of characters.

We know that GENES control the characters or traits first cellular DNA which is the information source synthesis of protein enzymes that works efficiently such that more hormones are produced which make the plants tall.

SEX DETEREMINATION It is the process by which sex of the offspring can be determined. There are two factors responsible for the determination of sex a) Environment.  b) Genetic

Enviromental factor is important in some animals temperature at which the fertilized eggs are kept decides the gender example Turtles.

Genetic factor plays its role in some animals like human being the gender of the individual is determined by the pair of chromosomes called sex chromosome.

XX Chromosome of female               XY Chromosome are of Male.

In human being there are 23 pairs of chromosomes out of these 22 pair of chromosomes are called autosomes and 23rd chromosome pair is called sex chromosome because it is the gender deciding of the individual.

During reproduction the female gametes fuses with male gamete the chromosome of male XY releases either X or Y and female releases X chromosome only when X chromosome of male and female combine the baby is GIRL and if X chromosome of female combines with Y chromosome of male than it is the possibility of birth baby boy.

sex det


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