Patterns of inheritance
Monohybrid inheritance
Key terms
Phenotype - the characteristics that are expressed.
Genotype - the alleles in your genome.
Heterozygous - two different alleles
Homozygous dominant - two of the same dominant
alleles
Homozygous recessive - two of the same
recessive alleles
Monohybrid inheritance
The inheritance of one gene =
monohybrid inheritance.
Use genetic diagrams to work out the
possible gametes and offspring.
In this example, both parents are
heterozygous for the tongue rolling
allele.
Four genotypes are equally possible,
the probability of each genotype is
0.25.
The ratio of the four genotypes is
1:1:1:1
Punnett square
Another way to work out the genotypes and
phenotypes off offspring.
One parent’s alleles at the top of the square, and
the other parent’s alleles at the side.
The dominant allele is always expressed.
The recessive allele is only expressed if there is
no dominant allele present.
The probability of each phenotype is 0.75 can roll
tongue, 0.25 can’t roll tongue.
The ratio of the phenotypes is 3:1.
Multiple alleles
Blood group A - IA IA or IA IO
Blood group B - IB IB or IB IO
Blood group AB - IA IB
Blood group O - IO IO
The gene for blood group has three alleles - IA, IB and IO.
Each blood group indicates which antigens are present on the surface
of red blood cells.
IA and IB are codominant alleles and IO is recessive.