Download Complex Patterns of Inheritance

Complex Patterns
of Inheritance
Exceptions to Mendel’s rules:
not simple dominant/recessive inheritance
Incomplete Dominance
The phenotype of the heterozygote is
INTERMEDIATE.
Red + White = Pink
Red parent plant
R
R’
R
RR’
RR’
RR’
RR’
White
parent
plant
R’
All pink offspring!
Codominance
Both alleles are expressed!
Red + White =
Both Red and White (NOT pink!)
Pleiotropy
The ability of a gene to affect an organism in
many ways, not just in one way.
• Example: Human disease PKU (phenylketonuria)
• Causes mental retardation and reduced skin & hair pigmentation
• Caused by mutation in gene for creating the enzyme that breaks
down the amino acid phenylalanine
• This mutation makes the person unable to break down
phenylalanine, leading to toxic levels that can damage the body in
many ways.
• PKU is manageable with medications and by following a diet free
of phenylalanine.
PKU patient
Epistasis
A gene at one location affects
the expression of a gene at
another location.
Coat color in mice:
BB & Bb (black)
bb (brown)
Gene that allows color to be deposited:
CC & Cc (color is present)
cc (albino)
Multiple Alleles
This is a gene that is controlled by more than
two forms of an allele
• Blood Types: A, B, AB, O
• A and B are codominant
• O is recessive to both
Type A: IAIA or IAi
Type AB: IAIB
Type B: IBIB or IBi
Type O: ii
Polygenic Traits
Trait controlled by two
or more GENES
(not alleles)
AaBbCc x AaBbCc
• Skin Pigmentation
• Height
Sex-Linked Traits
Humans have 46 chromosomes
22 pairs autosomes (pairs 1-22)
1 pair sex chromosomes (pair #23)
Males: XY
Females: XX
Sex-Linked traits are located on the X chromosome.
These traits tend to affect males more than
females. WHY??
Baldness
Colorblindness is a sex-linked trait.
People with normal vision should see a light
image of a red/brown sailboat.