Punnette’s square

• Reginald C. Punnett came up with the Punnett square.
• It is a square diagram which is used to predict the genotypes of a particular cross.
• During a breeding experiment, possible outcomes of offspring are studied using  Punnett squares.

Consider these examples of a Punnett squares:

Example 1 : Eye colour

• Parent 1 - Homozygous Dominant Brown colour eyes ( BB ).
  The 2 alleles B and B are written on one side of the square.
• Parent 2 - Homozygous Recessive Blue colour eyes ( bb ).
  The 2 alleles b and b are written on the other side of the square.
• Corresponding alleles are written in each box, one from each parent to find possible combinations .
• The offsprings in the F ₁ generation have all Heterozygous Brown colour eyes ( Bb )

Example 2: Pod colour of pea plant

• Plant 1 - Heterozygous Dominant Green pod ( Gg ).
  The 2 alleles G and g are written on one side of the square.
• Plant 2 - Homozygous Recessive Yellow pod ( gg ).
  The 2 alleles g and g are written on the other side of the square.
• Corresponding alleles are written in each box, one from each parent to find possible combinations.
• The offsprings have all Heterozygous Green pods ( Gg ) and Homozygous Recessive Yellow pods ( gg ) in the ratio 1:1