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CBSE Biology Subject Notes

CBSE Guess > eBooks > Class X > Heredity and Evolution By Mr. Ajay Kumar


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HEREDITY : - The transmission of characters from the parents to their offspring’s is called heredity.

VARIATION : - The differences in the characters among the individuals of a species in called variation. The great advantage of variations to a species is that it increases the chance of its survival in a changing environment.

CHROMOSOME : - Chromosome is a thread-like structure in the nucleus of a cell formed of DNA which carries the gene.

GENE : - A gene is a unit of DNA on a chromosome which governs the synthesis of one protein that controls a specific characteristic of an organism. Genes are actually units of heredity which transfer characteristics from parents of their offspring’s during reproduction.

DOMINANT GENE : - The gene which decides the appearance of an organism even in the presence of an alternative gene is known as a dominant gene. It dominated the recessive gene for the same characteristic on the other chromosome of the pair.

RECESSIVE GENE : - The gene which can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene.

GENOTYPE : - Genotype is the description of genes present in an organism and a pair of letters TT, Tt or tt.

PHENOTYPE : - The characteristic which is visible in an organism is called its phenotype and ‘tall’ or ‘dwarf‘.

FIRST FILIAL GENERATION OR F1 GENERATION : - When two parents to produce progeny, then their progeny is called first filial generation or F1 generation.

SECOND FILIAL GENERATION OR F2 GENERATION : - When the first generation progeny cross among themselves to produce second progeny, then this progeny is called second filial generation or F2 generation. 

HYBRID : - A new form of plant resulting from a cross of different varieties of a plant is known as a hybrid.


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Submitted By Mr. Ajay Kumar
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