Transcript When Heredity Follows Different Rules

When Heredity Follows
Different Rules
Horses and dogs are examples of animals
where breeders have created pure breeds.
In many plants, crossing
pure breeds results in
bigger and more
productive hybrids.
1) Complete Dominance
Mendelian Inheritance or complete
dominance - Occurs when heterozygous
and homozygous dominant individuals have
the **.
So…If T = Tall and t = short, then Tt and TT
** be tall
and if B = brown and b = blue, then Bb and
BB will both have brown eyes
2) Incomplete Dominance
• Occurs when the phenotype of the
heterozygous individual is a blend that of the
two homozygous individuals.
• Uses capitol letters for both dominant and
recessive. Use ‘ to distinguish recessive.
Example: a snapdragon plant
R = Red (dominant) allele
R’ = white (recessive) allele
Cross red (RR) with white (R’R’)
RR
R’R’
R’R’
RR’
RR’
RR
RR’
RR’
Genotype:
4 RR’ = 4 heterozygous
Phenotype:
PINK
The offspring are pink because that color is in between 2
homozygous phenotypes
Red (RR)
White (R’R’)
Offspring: All pink flowers
• An example of this in humans is hair type.
HH = curly
HH’ = wavy
H’H’ = straight
3) Co-dominance
This is when the phenotypes of both
homozygous individuals are expressed
equally in a heterozygous individual.
Example: feather color
B = black feathers
W= white feathers
X
=
• If we crossed a pure black (BB) with a pure
white (WW) what would we get?
B
W
BW
B
BW
Genotype:
4 BW = 4 heterozygous
Phenotype:
Black and white
BW
BW
W
BW = both black and white
X
=
Co-dominance in Humans
• Blood Type is an example of codominance
in humans.
• It is determined by the presence or
absence of antigens on surface of blood
cell.
• A and B are co-dominant and both are
dominant to type O.
What’s in your blood?...
Human Blood Types
Phenotype Genotype
Blood cell surface
molecules
Type A
IAIA or IAi
A molecule
Type B
IBIB or IBi
B molecule
Type AB
IAIB
A and B molecules
Type O
ii
No molecules
Blood Typing
• Alleles IA and IB –are co-dominant to each
other
• Allele i (type O) –is recessive to both IA
and IB
• O blood—universal donor
• AB blood—universal acceptor
Cross parent with heterozygous A ( IAi)
blood with a parent with heterozygous
B blood (IBi)
IA
IB
i
IAIB
IAi
i
IBi
ii
Genotype:
IAIB
IAi
IBi
ii
Phenotype (Blood type):
AB
A(carrier of O)
B(carrier of O)
O
Cross parent with type O blood (ii)with a
parent with homozygous B blood (IBIB)
i
IB
IB
IBi
IBi
i
IBi
IBi
Genotype:
4 IBi
Phenotype (Blood type):
B
Blood Facts
• Almost 40% of the population has O+ blood
• Patients with Type O blood must receive Type O blood
• About half of all blood ordered by hospitals in our area is Type O
• Type O blood is the universal blood type and is the only blood type
that can be transfused to patients with other blood types
• Only about 7% of all people have Type O negative blood
• Type O negative blood is the preferred type for accident victims and
babies needing exchange transfusions
• There is always a need for Type O donors because their blood may
be transfused to a person of any blood type in an emergency
Type
You Can Give
Blood To
You Can Receive
Blood From
A+
O+
B+
AB+
AOBAB-
A+ AB+
O+ A+ B+ AB+
B+ AB+
AB+
A+ A- AB+ ABEveryone
B+ B- AB+ ABAB+ AB-
A+ A- O+ O
O+ O
B+ B- O+ O
Everyone
A- OOB- OAB- A- B- O
Multiple Alleles
Multiple alleles--not all traits are only
controlled by 2 alleles, some traits are
controlled by several different alleles
– Example: In human blood typing there are
three alleles, A, B and O
Example. Mouse hair
color is controlled by
different alleles, black,
brown, gray, albino,
etc…
Polygenic Traits
• Poly = many -genic = genes
• Many traits are controlled by two or more
genes which often have 2 or more alleles.
– Examples: skin color, eye color, height
Let’s look at skin color. Let’s say only 3 genes (we’re
not sure how many) code for skin color and the alleles
would be:
AABBCC = dark skin color
aabbcc = light skin color
Any combination of those alleles would produce up to 7
different phenotypes (not including exposure to the sun)