Transcript Not-so-Simple Inheritance Patterns

Not-so-Simple
Inheritance
Patterns
Remember…
• Genes are
sections of a
chromosome
that have coded
instructions for
making proteins.
• Alleles are
different forms of
a gene.
Simple
Inheritance
• 2 alleles
• 2 phenotypes
• One allele is
dominant
• The other allele is
recessive
• The DOMINANT allele
completely masks the
recessive allele
Mendel Got Lucky
• In many ways Gregor
Mendel was quite lucky
in discovering his 4
genetic laws.
• He happened to use
pea plants.
• Things in nature aren’t
always so simple.
Not-so-Simple Inheritance
• 4 Main Types
– Codominance
– Incomplete Dominance
– Multiple Alleles
– Polygenic Traits
Codominance
• “Co” means together!
• Codominance = two
alleles are dominant
together.
• This produces a third
heterozygous phenotype
where BOTH traits are
Red Cow x White Cow 
expressed TOGETHER
Roan Cow
• Ex: Human Blood Type
Roan cattle have both
–A
red and white hairs
–B
mixed in together!
–O
– AB
Codominance
red x white  red & white spotted
Codominance
• Two alleles are expressed
(multiple alleles) in heterozygous
individuals.
• Example: blood type
1. type A = IAIA or IAi
2. type B = IBIB or IBi
3. type AB = IAIB
4. type O = ii
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Codominance Problem
Example: homozygous male Type B (IBIB)
x
heterozygous female Type A (IAi)
IA
i
IB
IAIB
IBi
IB
IAIB
IBi
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1/2 = IAIB
1/2 = IBi
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Another Codominance Problem
• Example: male Type O (ii)
x
female type AB (IAIB)
IA
IB
i
IAi
IBi
i
IAi
IBi
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1/2 = IAi
1/2 = IBi
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Codominance
Question:
If a boy has a blood type O and
his sister has blood type AB,
what are the genotypes and
phenotypes of their parents?
boy - type O (ii) X girl - type AB (IAIB)
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Codominance
• Answer:
IA
IB
i
i
IAIB
ii
Parents:
genotypes = IAi and IBi
phenotypes = A and B
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Incomplete Dominance
• Incomplete
Dominance =
neither of the two
alleles is
completely
dominant
• This produces a
third heterozygous
phenotype where
Amel & Ultra are incompletely
the traits are
dominant to each other.
BLENDED.
Amel x Ultra  Ultramel
Incomplete Dominance
red flower x white flower  PINK flower
Multiple Alleles
• Any of a set of three or
more alleles.
• Only two of alleles can
be present in a diploid
organism.
• Examples:
– Human Blood Type
– Human skin, hair, and eye
colors
Polygenic Traits
• Result of the interaction of several genes
• Human skin, hair, and eye color
– Influenced by more than one gene at different
locations on the chromosomes
• Human Blood Pressure
– Not just 1 “blood pressure” gene with several alleles
– Caused by several genes that control other traits such
as weight, cholesterol level, kidney function, etc…
• Human Height
– The combined size of all of the body parts from head
to foot determines the height of an individual.
Role of Environment
•
•
•
Our environment also plays a key role in
how traits are expressed.
Genes can be turned on/off due to
external environmental factors.
Examples:
–
–
–
–
–
Stress
Nutrition
Chemical exposure
Light
Temperature
BLOOD
TYPE
Genotypes
Can DONATE
TO:
Can
RECEIVE
FROM:
A
IA IA
or
I ai
A or AB
A or O
B
IB IB
or
IBi
B or AB
B or O
IA IB
AB
Anyone
(universal
recipient)
ii
Anyone
(universal
donor)
O
AB
O
Example of Environmental
Influence
• Human Height is heavily influenced by
hormones produced in the pituitary gland
and our diet during childhood and puberty.
• Usually, about 10% of an individual's
height is due to the environment.
Sample Questions
1. Predict the phenotypic ratios of offspring
when a homozygous white cow is crossed
with a roan bull.
2. What should the genotypes &
phenotypes for parent cattle be if a farmer
wanted only cattle with red fur?
Sample Questions
3. A cross between a black cat & a tan cat
produces a tabby pattern (black & tan fur
together).
a) What pattern of inheritance does this
illustrate?
b) What percent of kittens would have tan
fur if a tabby cat is crossed with a black
cat?
Sample Questions
1. A cross between a blue blahblah bird & a
white blahblah bird produces offspring that are
silver. The color of blahblah birds is determined
by just two alleles.
a) What are the genotypes of the parent
blahblah birds in the original cross?
b) What is/are the genotype(s) of the silver
offspring?
c) What would be the phenotypic ratios of
offspring produced by two silver blahblah birds?
Sample Questions
2. The color of fruit for plant "X" is
determined by two alleles. When two
plants with orange fruits are crossed the
following phenotypic ratios are present in
the offspring: 25% red fruit, 50% orange
fruit, 25% yellow fruit. What are the
genotypes of the parent orange-fruited
plants?