Download Incomplete Dominance

Incomplete Dominance
Neither allele is dominant over the
other
Heterozygous offspring have a
phenotype that is somewhere between
the two.
Incomplete Dominance
Incomplete Dominance
 Homozygous red parent: RR
crossed with
Homozygous white parent: WW
RR x WW
yields heterozygous offspring
RW that are pink
Incomplete Dominance
Codominance
 Both alleles contribute to the phenotype
 Heterozygous offspring express both
alleles
Codominance
X
Codominance: A black chicken crossed with a
white chicken results in a speckled chicken
CODOMINANCE:
ABO BLOOD TYPES
 Blood type depends on the presence
or absence of certain carbohydrates
on the surface of red blood cells
 3 alleles are possible:
 IA
 IB
 i
ABO BLOOD TYPES
 IA and IB are codominant to each
other when they are paired.
 i allele is recessive to both IA and IB
ABO Blood Groups
ABO Blood Groups
ABO Blood Types
 Blood typing is actually far more
complicated than “A”, “B”, and “O”
 ABO are the MAJOR antigens
 There are also MINOR antigens
 Rh factor: “+” or “-”
ABO Blood Types
ABO Blood Types
ABO Blood Types
ABO Blood Types
 Why is it important to get the right
blood type when getting a
transfusion?
 Transfusion Reactions
 Immune system (antibodies) will attack
cells that have an antigen that the body
doesn’t recognize as “self”
Transfusion Reaction
Multiple Alleles
More than 2 possible alleles exist in
a population
Multiple Alleles
 Coat color in rabbits: there are at least 4
different alleles
 C = full color (dominant to all other
alleles)
 c (ch) = chinchilla
 c (h) = himalayan
 c = albino (recessive to all other alleles)
Full color rabbit
Chinchilla rabbit: partial defect in
pigmentation
Himalayan rabbit: color in only certain parts
of body
Albino rabbit: no color; recessive to all other
alleles
Polygenic Traits
 Traits that are produced by the
interaction of more than one different
genes
Polygenic Inheritance
 For example: coat color in Labrador
retrievers is a result of interaction of 2
different genes.
Polygenic Inheritance
 Example: comb shape in chickens is a
result of interaction between 2
different genes.
X-Linked Inheritance
 Early 1900’s
 Thomas Morgan’s fruit fly studies
X-Linked Inheritance
X-Linked Inheritance
 More than 300 human traits are Xlinked.
 Most common X-linked recessive
disorders:




Hemophilia
Red-green colorblindness
Duchenne muscular dystrophy
Adrenoleukodystrophy (seen in the
movie Lorenzo’s Oil)
BARR BODIES
 Barr body is found only in females
 It is a darkly staining area in the
nucleus of a cell that represents an
inactivated X chromosome
 One X chromosome is randomly
inactivated
Barr Body
Barr Body
Do you see the Barr body?
Barr Body: X inactivation
 Calico cat
 Generally all females
 Have one X chromosome coding for for
gold color, and one X chromosome
coding for black color
 Color pattern shows how one X
chromosome in each cell is randomly
inactivated
Calico Cat
 There have been instances of male
Calico cats found
 How could this happen?
Male Calico cat?
 HINT: Male calico cats are sterile
Male Calico cat?
 Answer: Male Calico cats have XXY
chromosome configuration
 A Klinefelter’s cat? Yup, it happens.