Summary of Mendel’s Principles
1. Law of Dominance: Some alleles are dominant and
cover up the recessive alleles.
2. Law of Segregation: An organism has two alleles
for each gene but they can only pass on one.
3. Law of Independent Assortment: Genes found on
separate chromosomes are inherited independently
of each other.
Other Patterns of
Inheritance
There are many exceptions to
Mendel’s principles.
Incomplete Dominance: One allele
is not completely dominant over
another.
• Cause the two alleles to blend
together in a heterozygous
individual.
• Ex: If you cross a white flower
(WW) with a red flower (RR) the
offspring would have pink flowers
(RW)
Other Patterns of Inheritance
• Codominance: When both alleles in a heterozygous
individual are fully expressed.
– How is codominance different than incomplete
dominance?
– Example: When a black
chicken is crossed with a
white chicken all of the
offspring have white and
black feathers (This
phenotypes is called blue
on farms. Also note
offspring were not gray
feathers)
Other Patterns of Inheritance
• Multiple Alleles: for many traits there
are more than just two alleles that
exist in a populations.
– Each individual can still only have a
maximum of 2 different alleles per
gene.
Other patterns of Inheritance
– Example: Blood Types
Three different alleles that determine blood type: A, B and O.
Which alleles are dominant and which alleles are
recessive?
Keystone Practice