11.2 COMPLEX PATTERNS OF INHERITANCE
REFLECT
simple dominance--traits are either dominant or recessive
CONSIDER traits such as height
OBSERVE differences in height: shortest to tallest
HYPOTHESIZE: is height simple dominance?
Complex Inheritance of Traits
do NOT follow Inheritance Patterns Mendel Described
MENDEL’s EXPERIMENTS
-ALL 7 traits were simple dominance
-ALL 7 traits were inherited independently
EXCEPTIONS TO MENDEL’S LAWS
-INCOMPLETE DOMINANCE
-CO-DOMINANCE
-SEX LINKAGE
-MULTIPLE ALLELES
-POLYGENIC TRAITS
INCOMPLETE DOMINANCE
INCOMPLETE DOMINANCE-”blended” traits
Heterozygous genotype results in “mixture” of the 2 traits
R=red
r=white
then Rr = pink
R
r Rr
R
Rr
R
r
R RR Rr
r Rr
Rr
r Rr
100% pink
rr
25% red/50% pink/25% white
*different amounts pigment— R most  r least
INCOMPLETE DOMINANCE
CODOMINANCE
CODOMINANCE-”both” traits present in heterozygous
R=red cow r=white cow Rr=roan cow (red & white)
R
r Rr
R
Rr
R
r
R
RR Rr
r Rr
Rr
r
Rr
rr
100% roan
25% red/50% roan/25% white
*roan—BOTH red & white hairs
CODOMINANCE
CODOMINANCE
Sickle cell:
BB-normal
Bb=both
bb=sickle cell
SEX DETERMINATION
23rd pair chromosomes
determine gender
XX = FEMALE
50%
XY =MALE
50%
X
y
X XX
Xy
X XX
Xy
SEX LINKED TRAITS
-Genes are carried on the sex chromosomes
-Sex-linked genes on X chromosome ONLY
– XBXB normal female
– XBXb carrier female
– XbXb affected female
– XBY normal male
– XbY affected male
SEX LINKED TRAITS—
“X-LINKED”
SEX CHROMOSOMES—some genes only on larger X
chromosome, NOT on the smaller y chromosome
XB = dominant trait
Xb = recessive trait
XB
y
Red-green color-blindness
w/parents not CB (mom hetero)
males----Xby
females—XBXb
50% CB
0% CB
*8% males have red-green CB
rare in females
XB XB XB
XB y
XBXb
Xby
Xb
SEX LINKED TRAITS—
“X-LINKED”
Xb
y
XB
XBXb
XBy
Xb
XbXb
X bY
50% girls CB/50% boys CB
XB
Xb
XBXb
Y
Xby
Xb XBXb XbY
0 girls CB/100% boys CB
Exceptions to Mendel’s Laws
Sex Linkage
Sex linked Inheritance in Drosophila
MULTIPLE ALLELES
More than 2 possible alleles for a trait
ABO BLOOD TYPES
IA
PHENOTYPE/GENOTYPES
A
IAIA, IAi
IA
B
IBIB, IBi
IB
AB
IAIB
O
ii
i
IB
IAIA IAIB
-A- -ABIAIB IBIB
-AB- -BIAi
IBi
-A-B-
i
IAi
-AIBi
-Bii
-O-
MULTIPLE ALLELES
Blood
Group
(Phenotype)
Genotypes
Antibodies
Present in
Blood
Reaction When Blood from Groups Below Is Mixed with
Antibodies from Groups at Left
O
O
ii
Anti-A
Anti-B
A
IA IA
or
IA i
Anti-B
B
IB IB
or
IB i
Anti-A
AB
IA IB
A
B
AB
MULTIPLE ALLELES
IB
IA
i
IAIB
I Bi
i IAi
ii
AB / B / A / O
IA
IB
i
IAi
I Bi
i
IAi
I Bi
50% A / 50% B
HIEARCHY OF DOMINANCE IN ALLELES
-heirarchy of dominance in multiple alleles
Example: rabbit coloring
C
-full coat color
all black
Cch -chinchila
blended
Ch
-himilayan
spots
c
-albino
white
Order of dominance—
C > Cch > Ch > c
POLYGENIC TRAITS
MELANIN least
aabbcc
AaBbCc
most
AABBCC
POLYGENIC TRAITS- HAIR COLOR
THINK –PAIR- SHARE
-WHAT POSSIBLE EYE COLORS ARE THERE?
-blue, green, brown
EXAMINE EACH OTHER’S EYES
-What else do you notice about eye color?
HYPOTHESIZE:
Is eye color inherited in a simple dominant/recessive manner
-exact inheritance not determined
-polygenic models have been made
POLYGENIC TRAITS- EYE COLOR
POLYGENIC TRAITS
HETEROCHROMIA IRIDIUM—2 different color eyes
Can result from trauma to the eye
Can be a altered gene