The genotype is the genetic information we deduce from the phenotype.
It is usually represented by two letters.
Each gene responsible of a character can exist in different versions -we call it alleles- , which are associated with a certain phenotype.
As each of us have two alleles for each gene, we represent our genotype by two letters.
As we can show only one phenotype, the resulting phenotype will result from the combination of our two alleles, depending on the relationships of dominance or recessivity between the alleles, and the heredity pattern.
For a single gene, we can have four main inheritance patterns:
To determine if a character is following a determined pattern, we should assume this pattern and follow the following steps.
Two possibilities:
Even if you have found a consistent model, you have to test the rest of the models to discard that two models are consistent at the same time: it woul mean that, even if only one model is driving the inheritance of this character, you are not able to determine which it it. Don't worry: to discard some models is also information!
Look at the videos to learn how to discard heredity models from a pedigree.
Test your abilities with the following exercises:
Image extracted from: Michael Gregory Website
More training exercises at: Michael Gregory's Pedigree Exercises.