More Patterns of
Inheritance
Incomplete Dominance
• A cross where neither allele is dominant
over the other.
• The traits appear to be blended together.
• Ex. Snapdragon flowers
• RR=Red
• WW=white
• RW=pink
Bay is brown with black.
The Cream Dilution Gene
Is white when
homozygous.
What will it do to horses?
brown with black.
CREAM and BROWN
produce
New color: BUCKSKIN
What Pattern of Color Inheritance
Does this show?
Cream dilutes red-brown
To make….
PALOMINO, a golden color.
Incomplete
Dominance
Codominance
• A cross where both alleles are
equally expressed.
• Ex. Horse Coats
– CBCB=Brown coat
– CWCW=White coat
– CBCW=Roan coat: has both brown and white
hairs.
Co-dominance
Andalusian Chickens
• Black feathers and white feathers are co-dominant.
• Cross FB FB and FW FW and what will be produced?
Andalusian Chickens
Q: Cross FB FB and FW FW and what will be produced?
A: A Steel Blue
Chicken FB FW
Do this:
1.Cross a heterozygous red rose
with a homozygous recessive
yellow rose. Red is the dominant
allele. What are the possible
colors of offspring?
X
What will the
offspring look like?
2. A farmer is planning to mate a
bull and cow. The male has a
roan coat (brown and white
hairs) and the female has a white
coat (white hairs). What might
their calves look like?
X
What will the offspring look like?
3. Your parents have decided to
plant some snapdragons and
want to know why there are three
colors – red, pink and white.
You volunteer to explain it to
them by showing them the cross
of 2 hybrid pink snap dragons –
what are the possible offspring?
4. You and your partner carry sickle cell trait.
What are your chances of having a baby with
sickle cell anemia?
Use RR for normal blood. RS for carriers and SS
for sickle cell anemia.
Sickle Cell Anemia
Normal
Carrier
5. Two heterozygous parents with free earlobes
have 4 children predict the genotypes and
phenotypes for the children’s ears.
F = free ear lobes
ff = attached ear lobes
X
Hybrid
Hybrid
X
Hybrid
Hybrid
Warm-Up
• No blurting – give everyone a chance
• Decide if the pictures are examples of:
– Simple dominance
– Incomplete dominance
– Codominance
Andalusian Chickens
Warm-Up
• Complete this problem in your journal:
– If a man an a woman are having a baby,
what are the chances the baby will be a
boy? Use a Punnett Square to justify
your answer. Hint: Think about which
chromosomes a male has and which ones a female
has
Blood Types are an example of
co-dominance
Human Blood Types
Phenotype:
The protein
A
Genotype:
The genes
IAIA or IAi
B
IBIB or IBi
AB
IAIB
O
ii
Blood type rules
•
•
•
•
A is dominant over O
B is dominat over O
O is recessive to A and B
A and B are co-dominant to each other.
X-Linked Genes
• Genes that are located on the X sex
chromosomes.
• Males will have one copy of the gene.
Normal male- XB Y
Affected Male- Xb Y
• Females Will have 2 copies of the gene:
Normal Female – XB XB
“Carrier” Female – XB Xb
Affected Female – Xb Xb
Gender Determination
Y
X
• (Very few genes are found on the
Y Chromosome)
• Only females can be carriers for
sex-linked disorders on the X.
Carrier – a person who transports the
recessive allele but does not show the
recessive trait.
*Are they heterozygous or homozygous?*
X Chromosome
• Recessive genes found there:
c
– Colorblindness X
b
– Baldness X
– Hemophilia - bleeding disorder where blood
h
won’t clot. X
A male with the XbY will have the
recessive trait for baldness.
Polygenic
• A trait that is produced (controlled) by two
or more genes
Eye Color Example
• Controlled by at least three genes.
• Act together to produce your eye color
Lethal Genes
• Any genetic trait that causes death.
Examples:
Hemophilia- bleed to death
Huntington’s disease- brain shrinks
Lethal Genes
Hemophilia (lethal and sex-linked)
bleed to death
X hY
Lethal Genes
Huntington’s disease- brain shrinks