Hon Bio Genetics Non and Co dominance

Exceptions to Mendel’s
principles:
•Phenotype can be affected by
more than genotype.
•Not all genes show a pattern
of dominance and
recessiveness.
•For some genes, there are
more than two alleles.
•Many times, traits are
controlled by more than one
gene.

Incomplete Dominance or Nondominance
All traits are not
fully dominant or
recessive traits.
Some genes
appear to:
blend together.
For example: In some flowers, such as
snapdragons, a homozygous red flower crossed
with a homozygous white flower yields a
heterozygous pink flower.
This is known as incomplete dominance or
nondominance.
In this case, no allele is dominant or recessive -
they blend together in the offspring.
Since there is no recessive allele, use only capital letters. For example: A red flower
would be RR, a white flower would be WW and the pink hybrid would be RW.

R
W
R
W
RW RW
RW RW
RR WW RW
Notice there is no Dominant trait
here and so there is a blending of
both traits in the F1 generation.
This is referred to as
Incomplete Dominance
4 RW
Or
100% RW
4 Pink
Or
100% Pink

What type of offspring might be produced by two pink flowering plants?
What are the genotypes of the parents?
R
R
W
W
1 Red
2 Pink
1 White
1 RR
2 RW
1 WW
RR RW
RW WW