Download Genetics

Incomplete Dominance
& Codominance
Regents Biology
2007-2008
Incomplete Dominance
 In incomplete dominance, neither allele is
dominant so there is a blending of
__________
traits when two different alleles for the
______
same trait occur together.
 Colors blend together
heterozygous
 (______________
individuals = 3rd phenotype)
Regents Biology
red
pink
white
Incomplete Dominance
 In Four O’ Clocks, if you cross a red RR
_____
WW
(which is always pure) with a white _____
(that is also always
pure) , you get a
RW (which
pink _____
is always hybrid /
heterozygous
RW
RW
RW
Regents Biology
RW
Incomplete dominance
P
X
true-breeding
red flowers
true-breeding
white flowers
100% pink flowers
1st
100%
generation
(hybrids)
self-pollinate
25%
red
2nd
generation
Regents Biology
50%
pink
25%
white
1:2:1
Incomplete dominance
RW x RW
%
genotype
male / sperm
female / eggs
R
R
W
RR
W
RR
RW
RW
25% 25%
50% 50%
RW
RW
WW
WW
25% 25%
1:2:1
Regents Biology
%
phenotype
1:2:1
Incomplete Dominance
RR and blue
 In another flower, if red ____
BB flowers are crossed, they produce
____
RB flower
a 3rd purple ____
 What would be the genotype ratio and
phenotype ratio if you crossed two
purple flowers…?
Regents Biology
Incomplete Dominance
 Cross of two purple flowers
RB X ____
RB
____
 What are gamete possibilities?
R
 genotype ratio
RR
1RR : 2RB : 1BB
R
red
 phenotype ratio
1red : 2 purple : 1 blue
RB
B
purple
 Can you have a
heterozygous red or
Regents Biology
no
hybrid blue flower? ___
B
RB
purple
BB
blue
Codominance
alleles contribute to the phenotype
 Both _______
of the organism by showing
up simultaneously (at the
same time) in heterozygous
individuals.
 In cattle and horses, if you
cross a pure ____
red (RR) with
a pure ______
white (WW), you get
(RW) which produces the
color roan
_____.
Regents Biology
Codominance
 These cattle or horses actually have both
red and white hairs intermixed, or are
spotted. Roan is a third ___________.
phenotype
 If you cross a roan with a white…
R
W
W
RW
roan
WW
white
W
RW
roan
WW
white
Regents Biology
Codominance
 Andalusian chickens also show this

pattern of inheritance.
If you cross a black (BB) chicken with a white
(WW) chicken, you get black+white speckled
(BW) chicken
Regents Biology
Multiple Alleles
 Blood type in humans is an example of this
inheritance pattern.
four different
 The ______
blood groups:
 A, B, O, and AB
 Are produced
three different
by ______
alleles:
 A, B, and O
Regents Biology
Phenotype
Genotype
A
AA or AO
B
BB or BO
AB
AB only
O
OO only
Genetics of Blood type
phenogenotype
type
A
B
antigen
on RBC
antibodies
in blood
donation
status
A A or A i
type A antigens
on surface
of RBC
anti-B antibodies
__
BB or B i
type B antigens
on surface
of RBC
anti-A antibodies
__
AB
both type A &
type B antigens
on surface
of RBC
no antibodies
universal
recipient
ii
no antigens
on surface
of RBC
anti-A & anti-B
antibodies
universal
donor
AB
O
Regents Biology
Blood donation
clotting clotting
clotting
clotting
Regents Biology
clotting
clotting
clotting
Multiple Alleles
 Examples of Blood type crosses
Regents Biology
Environment effect on genes
 Phenotype is controlled by
both environment & genes
Human skin color is
influenced by both genetics
& environmental conditions
Color of Hydrangea flowers
Regents
Biologyby soil pH
is
influenced
Coat color in arctic
fox influenced by
heat sensitive alleles
Sex-Linked Traits
 Sex Determination
Females – XX
 Males – XY

X
X
X
Y
 Almost all sex-linked traits are
found on the X chromosome
 Y chromosome contains very
few genes and is mainly
involved in sex determination
Regents Biology
Sex-Linked Traits
 It is possible for a
female to be a
carrier of an Xlinked trait, but not
express it
 Men will express
all X-linked traits
they inherit
Regents Biology
X-linked recessive, carrier mother
Unaffected
father
Carrier
mother
Unaffected
Affected
Carrier
Unaffected
son
Unaffected
daughter
Carrier
daughter
Affected
son
Sex-linked traits
 Sex chromosomes have other genes on
them, too
especially the X chromosome
 hemophilia in humans

 blood doesn’t clot

Duchenne muscular dystrophy in X
humans
X
 loss of muscle control

red-green color blindness
 see green & red as shades of grey
Regents Biology
X
Y
sex-linked recessive
Sex-linked traits
2 normal parents,
but mother is carrier
HY x XHh
H Xh
XHH
male / sperm
XH
XH
Y
XH
XH XH
XH Y
Xh
XH Xh
XhY
Y
XH
XH Xh
Xh
Regents Biology
female / eggs
XH Y