Monohybrid Inheritance

A cross between two parents who possess different forms (alleles) of a gene is called monohybrid inheritance.
Here are some key terms to remember related to monohybrid inheritance:
Genotype - The alleles of genes that is inherited from parents
Phenotype - The charectieristic a person displays (eg. hair colour)
Dominant - The "stronger" charectiristic that will always be shown in the phenotype.
Reccesive - The "weaker" charectiristic that will be masked unless two reccesive alleles                      are present
Co-Dominance - When both alleles are expressed in an indiviual e.g AB blood
Homozygous - Identical pairs of alleles of a gene e.g RR
Heterozygous - Two different pairs of alleles of a gene e.g Rr
Example Question
The gene for albinism is recessive. If an albino male has a child with a heterozygous   non-albino female what are the chances that there child is an albino.
 Firstly create a punnet square:
A a
a Aa aa
a Aa aa
We can evaluate from this that half the children would be Aa and half would be aa therefore the chances of them having an albino child is 50%.
Incomplete Dominance
This is when the reccesive allele has a partial effect on the dominant gene for example in sickle cell anaemia. If a individual has sickle cell anaemia then the haemoglobin they make is called haemoglobin S and is inefficient at carrying oxygen. if an individual is homozygous for the mutant allele there red blood cells also appear sickle shaped and tend to stick together and are less flexible. However of an individual is heterozygous for the mutant allele they possess both types of haemoglobin and there red blood cells are not sickle shaped. This is sickle cell trait. This is a good example of incomplete dominance to remember for the exam.
This is when both alleles are expressed in an individual. For example in blood groups. blood groups A and B are completely dominant to blood group O but are co-dominant to each other. This results iin the following types of blood.
Genotype  Blood Group