Class 10 Heredity And Evolution Notes
CBSE Class 10 Heredity And Evolution Notes
CBSE Class 10 Heredity And Evolution Notes PDF
Heredity :- The process of transfer of characters or traits from the parents to their offsprings is called heredity.
Variations :- The differences between the characters or traits among the individuals of the same species are called variations. For example human height is a trait which shows different variations like tall, short, medium etc.
Another example is earlobe, it shows two variations free earlobe and attached earlobe.
The variation is necessary for evolution The great advantage of variation is that it increases the chance of survival in a changing environment
Accumulation of variations during reproduction
The reproduction produces variations in offsprings .
The minor variations are seen due to inaccuracies in DNA copying.
These variations are less in asexual reproduction and more in sexual reproduction.
Some variations are useful variations and they help the organism to adjust to the changes in the environment.
Some variations do not help the organism to adjust to the changes in the environment and they may die and become extinct
Transfer of characters
Characters are transferred through DNA molecules present in the gene on the chromosomes which are present in the nucleus of the cell.
The inheritance of characters is due to the fact that both the father and mother contributes equal amount of genetic material to the child.
So for each trait there are two factors one from the father and one from the mother
The structure of the chromosome
CHROMOSOME: A thread like structure in the nucleus of cell formed of DNA and protein
which carries the genes.
GENE: A unit of DNA or a segment of DNA which controls specific characteristic of an
organism.
ALLELES: They are various forms of a gene which occur at the same particular position or
locus over the chromosomes.
DOMINANT GENE: The gene which decide the expression of a character even in the presence of an alternative gene.
RECESSIVE GENE: The gene which decides the expression of an organism in the presence of another identical gene.
The dominant gene is represented by a capital letter and the corresponding recessive gene is represented by the same letter in small.
For example the dominant gene for tallness is represented by T and the recessive gene for dwarfness is represented by t.
Genotype:- The genotype is the description of genes present in an organism.
Phenotype:- The characteristic or trait which is visible in an organism Is called phenotype. Ex- Tall or dwarf.
Rules for the Inheritance of Traits – Mendel’s Contributions
Mono-Hybrid Crossing
Gregor Johann Mendel conducted experiments with garden pea plants and determined the rules for the inheritance of traits
Mendel selected pea plants having one pair of character – a tall pea plant and a
short pea plant.
He selected pure tall (TT) and pure short (tt) pea plants and cross pollinated them.
He obtained all tall plants (Tt) in the first generation (F1 )
When the first generation plants were self pollinated, he obtained tall and dwarf
plants in the ratio 3:1 in the second generation. (F2)
The ratio of pure tall (TT), hybrid tall (Tt) and pure dwarf (tt) was in the ratio 1:2:1
The trait that is expressed in the F1 generation is called the dominant trait and the trait that is suppressed in the F1 is called the recessive trait.
Dihybrid cross
When plants having two pairs of characters (Eg:- shape and colour of seeds) were crossed (Dihybrid cross)
Mendel selected pea plants having two pairs of characters – shape and colour
of seed.
He selected plants having round yellow seeds (RRYY) and wrinkled green seeds (rryy) and cross pollinated them.
He obtained all plants with round yellow seeds (RrYy) in the F1 generation.
When these plants were self pollinated in the F2 generation out of 16 plants, 9 had round yellow (RrYy), 3 had round green (Rryy), 3 had wrinkled yellow (rrYy) and 1 had wrinkled green (rryy) seed In the ratio 9:3:3:1
CBSE Class 10 Heredity And Evolution Notes PDF
