Biology Principles of inheritance and variation class 12 Part 3 Notes

Punnett Square

• It was developed by british geneticist Reginald punnett.
• A Punnett square is a graphical representation of the possible genotypes of an offspring arising from a particular cross or breeding event

•Some terms are often used in the study of genetics and these are particularly useful in understanding squares. Among these is the term ‘allele’ and is used to denote a variant of a gene.
the function of Punnett

•For example, a pea plant can have red or white flowers and the gene variants coding for each of these is called an allele.

Test Cross :-

• It is the cross that is made to know whether a trait is homozygous (TT) Or heterozygous (Tt) dominant by its cross with recessive trait.
• In this cross, the organism with unknown dominant genotype is crossed with the recessive parent.
• This cross finds out the homozygous and heterogygous nature of the genotype.

Example :-

Q1) If we want to determine the genotype of violet flowered pea plant.

Then it is crossed with the recessive parent (white flowered pea plant) instead of self crossing.

Example :-

Q2) A cross is carried out between two pea plant showing the contrasting traits of height of the plant.

The result of the cross showed 50% of parental characters Work out the cross with the help of punnett square.

Example :-

A Q 3 )Work out the cross to find out the genotype of pea plant.