Alleles of a gene can carry the same instructions or different instructions. You can only inherit two alleles for each gene, and they can be the same or different
‘Show the possible allele combinations of the offspring produced when a pure breeding short plant is bred with a pure breeding tall plant’
A pure-breeding genetic cross in pea plants
‘Show the possible allele combinations of the offspring produced when two of the offspring from the first cross are bred together’
A genetic cross diagram (F2 Generation)
‘Show the results of crossing a heterozygous plant with a short plant’
A cross between a heterozygous plant with a short plant
How to construct Punnett squares
You should always write the dominant allele first, followed by the recessive allele.
If you are asked to use your own letters to represent the alleles in a Punnett square, try to choose a letter that is obviously different as a capital than the lower case so the examiner is not left in any doubt as to which is dominant and which is recessive.
For example, C and c are not very different from each other, whereas A and a are!
A family pedigree chart
‘A plant breeder has a tall plant of unknown genotype. How can they find out whether it is homozygous dominant or heterozygous?’
Determining genotypes from offspring