B1 Explaining inheritance - Punnett squares

Punnett squares are also called Genetic diagrams. Useful for showing the probability of organism getting a certain allele. Who cares - you might say. Well it is useful not only for plant breeders but for working out the probability of someone giving birth to a baby with a genetic disease like sickle cell disease or cystic fibrosis.

Look at the example of the flowers Both parent flowers have the same phenotype and genotype. Thet are both phenotype purple and genotype Bb.

Notice, that one of the flowers is white. That is because it has received one recessive white allele from the pollen and one recessive white allele from the egg.

This gives it a probability of 1/4 = 0.25 being white or 0.25 X 100 = 25%