complex patterns of inheritance exceptions to mendel’s rules: not simple dominant/recessive...
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Complex Patterns Complex Patterns of Inheritanceof Inheritance
Exceptions to Mendel’s rules:Exceptions to Mendel’s rules:
not simple dominant/recessive inheritancenot simple dominant/recessive inheritance
Incomplete DominanceThe phenotype of the heterozygote is
INTERMEDIATE.
Red + White = Pink
RR’ RR’
RR’ RR’
R R
R’R’
R’R’
Red parent plant
White White parent parent plantplant
All pink offspring!
CCooddoommiinnaanncceeBoth 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 and Codominance
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 B: IBIB or IBi
Type AB: IAIB Type O: ii
Polygenic Traits
Trait controlled by two or more GENES
(not alleles)
AaBbCc x AaBbCc
• Skin Pigmentation• Height
Sex-Linked TraitsHumans 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.
Epigenetics