Beyond Mendel
• Mendel discovered that in some traits, one allele is
dominant over the other allele (we call this simple
dominance)
• However, many traits do not work like that
• Ex.
• Incomplete dominance
• Codominance
Incomplete Dominance
• Neither trait is dominant or recessive
• A heterozygous individual will have a blend of the two traits
• Ex. Snapdragons
• Instead of using R and r, we use
FR and FW to show incomplete
dominance
Red = FR FR
Pink = FR FW
White = FW FW
Incomplete dominance example
• Cross a red flower with a
white flower:
• If we crossed two plants
from the F1 generation, we
would get:
Co-dominance
• BOTH alleles for a trait are dominant
• A heterozygous individual expresses both
traits
• Ex. Black rooster breeds with a white hen
Black: FBFB
White: FWFW
The F1 are all “barred”
(black and white feathers)
Example
• In four o’clock plants, red flowers are incompletely
dominant over white flowers.
• Heterozygous flowers are pink.
• If a red flower is crossed with a white flower, what
is the colour of:
a)The F1 generation?
b)The F1 generation crossed with the red parent?
c)The F1 generation crossed with the white parent?
Example 2
• A cross between a yellow snake & a blue snake
produces offspring that are all green:
a)What are the genotypes of the parent generation (P)?
b)What are the genotypes of the F1 generation?
c)What would be the phenotypic ratios of offspring
produced by two green snakes?
Sickle cell anemia
• An inherited genetic condition
that results in a decrease in the
ability of red blood cells to carry
oxygen
• Sickle red blood cells become hard
and irregularly shaped
• Become clogged in blood vessels
• Causes excruciating pain,
damage to body organs and even
death
Sickle cell anemia
• If you are a carrier of sickle cell anemia, you have
higher resistance to malaria – a deadly disease
caused by a protist, common in warm areas
• Sickle cell carriers have a survival advantage
compared to those who do not
• Therefore, the allele for sickle cell is passed on
more frequently
Polygenic inheritance
• Some traits are a result of a
combination of many genes
• Ex. Height, skin colour, eye
colour
• Depending on which alleles
you inherit for each of these
genes, your traits may fall
inside a great range
Polygenic inheritance
Polygenic inheritance