More Punnett squares
Complete Dominance
•Involves dominant and recessive alleles
•dominant allele always overpowers the
recessive allele in appearance
Incomplete Dominance
• Neither allele is dominant or recessive
• Organisms with two different phenotypes
produces offspring with a third phenotype
that is a blending of the parents
Incomplete Dominance
• Ex: Cross a red flower (RR) with a white flower
(WW) and the offspring will be pink (RW)!
Incomplete Dominance
(RR) and blue ____
• In another flower, if red ____
(BB)
flowers are crossed, they produce a 3rd purple
____ flower(RB)
• What would be the genotypic ratio and
phenotypic ratio if you crossed two purple
flowers?
Incomplete Dominance
• Cross of two purple flowers
_RB_ X _RB_
• What are gamete possibilities?
• genotypic ratio
1RR : 2RB : 1BB
R
• phenotypic ratio
1red : 2 purple : 1 blue
B
R
B
RR
RB
red
purple
RB
BB
purple
blue
Codominance
• Neither allele is dominant or recessive
• Parents with different phenotypes produce an
offspring with a third phenotype
– Third phenotype will show both parental
phenotypes simultaneously (at the same time)
Codominance
• In cattle and horses, if you cross
a pure red (RR) with a pure
white (WW), you get (RW)
which produces the color roan.
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…
• RW X WW
R
W
W
RW
roan
RW
roan
W
WW
white
WW
white
What is it?!
+
=
+
=
Multiple alleles
• two or more possible alleles for the same
gene within a population
• Thus multiple alleles
• However, individuals within the population
are only able to hold two of them
• Non-human examples: rabbit fur color, mice
skin color, eye color in flies, wing size in flies
Multiple Alleles
• Blood type in humans
• The _four_ different
blood types:
Phenotype
Genotype
– A, B, O, and AB
• Blood types are produced
by three_ different
alleles:
– A, B and O
A
AA or AO
B
BB or BO
AB
AB only
O
OO only
Genotype for
Blood Type
I and i used in genotype
I used with A and B
i used with O
A and B are dominant
over O: A and B are
codominant
Ex: Genotype: AA is IAIA
Blood type chart
PHENOTYPE
GENOTYPE
A
A
B
B
AB
O
AA, IAIA
AO, IAi
BB, IBIB
BO, IBi
AB, IAIB
OO, ii
Blood type AB is an example of codominance in humans
Blood Type Punnett Square
• Draw a Punnett square showing all the
possible genotypes for the offspring produced
by a type “O” mother and an a Type “AB”
father.
i
i
Cross: ii x IAIB
IA
IAi
IAi
IB
IBi
IBi
Blood Type Punnett Square
• Cross a female with blood type A and a male
with heterozygous B blood type.
• Complete ratios (phenotypic and genotypic)
• A male with blood type B has a child with a
woman who has blood type A. The child is
blood type O. What is the genotype of the
male and female? Show your work.
How does blood type work?
Blood transfusions
Rh factor: Rh for Rhesus Monkey
• Positive vs Negative Blood types
• Positive: protein is present
• Dominant trait
• Negative: protein is absent
• Recessive trait
Polygenic traits
• Traits controlled by two or more genes (one
gene has two alleles)
• Show a wide range of phenotypes
• Phenotype is produced by the interaction of
more than one pair of alleles
Examples of polygenic traits in
humans
Example of polygenic traits in
humans
Examples of polygenic traits in
humans
Sex-linked traits
• Every new born has a 50% chance of being
female and a 50% chance being male
– DAD: X Y
• Sperm contains either:
X
or
Y
– MOM: X X
X
Y
X
XX
XY
X
XX
XY
• Eggs all contain: X
Sex-Linked traits
• The X chromosome contains many genes,
whereas the Y chromosome contains only a
few genes
• sex-linked genes: genes located on one of the
sex chromosomes (X or Y) but not the other
• most sex-linked genes are X-linked genes
Examples of sex-linked traits:
X-linked
• Colorblindness: more common in males than
females
• Hemophilia: more common in males than
females
Both colorblindness and Hemophilia are
recessive traits
Colorblindness
Do any of these pictures look the
same?!
Test time!
Colorblind: X-linked trait
• C- normal vision
• c- colorblind
• You must incorporate XX (mom) and XY (dad)
• This is how to set it up:
• (remember colorblindness is X-linked!)
Normal vision
Female: XX
Male: XY
Heterozygous
(carrier)
Colorblind
Punnett Square
• Cross a female who is a carrier for
colorblindness with a normal vision man.
• Cross a normal vision woman (homozygous)
with a colorblind man.
Hemophilia: X-linked recessive trait
• Hemophilia is the inability for blood to clot
– Your blood clots every time you get a papercut
–H: normal clotting
– h: hemophilia
– Make a key for hemophilia:
• Normal female:
• Female Carrier:
• Female with hemophilia:
Normal Male:
Can a man be a carrier?
Male with: