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Genetics-theory Biology Target-ssc-cgl-2018 Tier 1

Genetics-theory Biology Target-ssc-cgl-2018 Tier 1


  • Genetics is the branch of science which deals with the inheritance as well as the variation of characters from parents to offspring.
  • Inheritance is the process by which the characters of parents are passed to the offspring.


  • Gregor Mendel conducted an experiment on “garden peas” and proposed “laws of inheritance”.
  • He noticed that something can be passed to offspring from parent , over successive generations, through gametes. He called these things as ‘factors’. Now these factors are known as genes.
  • Genes are the unit of inheritance.

Law of Dominance :

  • Factors are responsible for characters and these factors occur in pairs.
  • If the factors in a pair are dissimilar, the dominant pair dominates the recessive one.

Law of Segregation:

  • This law states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.

Law of recombination:

  • Two characters determined by two unlinked genes are recombined at random in gametic formation, so that they segregate independently of each other, according to the first law.


  • Linkage : It is an exception of Mendel’s law. In linkage, two different gene are present on the same chromosome and they express themselves together instead of independently.
  • Mutation : Mutation is referred as a sudden change in the gene which is heritable from one generation to another.
  • Variation : Change in characters by recombination of gene in offspring is known as variation. Due to this, a child looks different from its parents.
  • Cloning : It is a process in which many identical organisms from a single cell, which have same genetic characters, are produced.
  • Autosomes : Chromosomes responsible for characters other than sex are called autosomes.
  • Sex chromosomes : Chromosomes responsible for sex determination.
  • Muton : Unit of gene responsible for mutation.
  • Recon : Unit of gene which take part in recombination.


  • Chromosome decides the sex of an individual.
  • A normal human being has 23 pairs of chromosomes out of which 22 pairs are autosomes and the remaining 1 pair is sex chromosome.
  • Males consist of XY chromosomes while females consist of XX chromosomes.
  • When X chromosome of male pairs with any of the X chromosome of female, it produces a female child.
  • When Y chromosome of male pairs with any of the X chromosome of female, it produces a male child.


Genetics-theory Biology
Haemophilia :

  • X-linked genetic order.
  • This disease affects the clotting of blood. Any cut will result in non-stop bleeding.

Down’s syndrome :

  • When an extra chromosome is added to 21st autosomal chromosome this lead to develop Down’s syndrome also called 21 trisomy.
  • The person is mentally retarded; eyes are protruded an irregular physical structure is present.

Klinefelter syndrome :

  • When a male have an extra X or Y chromosome in sex chromosome then the condition will be XXY or XYY instead of XY.
  • This syndrome can lead to lower production of testosterone, reduced muscle and etc.

Edwards syndrome :

  • It is also known as 18 trisomy caused by the presence of all, or part of a third copy of chromosome 18.
  • Causes developmental delay.

Sickle cell Anaemia :

  • In this disorder erythrocytes destroyed more rapidly than normal leading to anaemia.

Turner syndrome:

  • Single sex chromosome (X0)


  • It is an inborn error of metabolism which result in mental retardation.

Colourblindness :

  • This disorder lead to failure of distinguished red and green colour.
  • The gene responsible for this diseases is situated on sex chromosome.

Terminologies of Biology:

  • Anatomy:  study of internal structures of organisms.
  • Apiculture:  Rearing of honey bee for honey.
  • Andrology:  study of male reproductive organ.
  • Cardiology:   study of heart.
  • Dermatology:  study of skin.
  • Gynecology:   study of female reproductive system.
  • Haematology:   study of blood.
  • Hepatalogy:   study of liver.
  • Neurology:  study of nervous system.
  • Nephrology:  study of kidneys.
  • Odontology:   study of teeth and gum.
  • Osteology:  study of bones.
  • Oncology:  study of cancer and tumors.
  • Ophthalmology:  study of eyes.
  • Ornithology:   study of birds.

Genetics-theory Biology

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