3.20 predict the probabilities of outcomes from monohybrid crosses

The each parent gives one allele to the offspring. There are two possible alleles it could give (for example, 'Bb' there is 'B' and 'b'). Therefore, if there are two parents, and each parent can give a possibility of one of two alleles, this means there are 4 possibilities overall for the offspring. I explained that so oddly, here is a diagram which will probably help more...



 

If you are asked to work out the probability of a child inheriting a genotype/phenotype, just count how many times it comes up and divide it by 4 (then x by 100 to get a %).

For example, if you are given the diagram above and asked to work out the probability the offspring will inherit 'Bb'. First you count how many 'Bb' are present, the answer is 2.Now divide 2 by 4 (this is because there are 4 possibilities) = 0.5. Now x0.5 by 100 to make a %. 0.5 x 100 = 50. So there is a 50% chance the offspring will inherit 'Bb'.

Image credit: scienceaid