Download Not-so-Simple Inheritance Patterns

Not-so-Simple
Inheritance
Patterns
#1 and #2 Remember…
• Genes are
sections of a
chromosome
that have coded
instructions for
making proteins.
• Alleles are
different forms of
a gene.
#3 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
#4,5,& 6
• “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
#7 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
copyright cmassengale
8
#7 Codominance Problem
Example: homozygous male Type B (IBIB)
x
heterozygous female Type A (IAi)
IA
i
IB
IAIB
IBi
IB
IAIB
IBi
copyright cmassengale
1/2 = IAIB
1/2 = IBi
9
Another Codominance Problem
• Example: male Type O (ii)
x
female type AB (IAIB)
IA
IB
i
IAi
IBi
i
IAi
IBi
copyright cmassengale
1/2 = IAi
1/2 = IBi
10
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)
copyright cmassengale
11
Codominance
• Answer:
IA
IB
i
i
IAIB
ii
Parents:
genotypes = IAi and IBi
phenotypes = A and B
copyright cmassengale
12
Incomplete Dominance
#8,9, & 10
• 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
#11 & 12
• 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 #13 &14
• 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 #15
•
•
•
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
Work on Pages 18-22 in your
packet. Follow directions.
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