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
• In another flower, if red ____ and blue ____ flowers are crossed, they produce a 3rd purple ____ flower
• What would be the genotypic ratio and phenotypic ratio if you crossed two purple flowers?
(RR)
(RB)(BB)
Incomplete Dominance
• Cross of two purple flowers_RB_ X _RB_
• What are gamete possibilities?• genotypic ratio 1RR : 2RB : 1BB1RR : 2RB : 1BB• phenotypic ratio 1red : 2 purple : 1 blue1red : 2 purple : 1 blue
RRred
RBpurple
RBpurple
BBblue
R
B
B
R
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
RWroan
WWwhite
RWroan
WWwhite
R
W
W
W
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: – A, B, O, and AB
• Blood types are produced by three_ different alleles: – A, B and O
Phenotype Genotype
A AA or AO
B BB or BO
AB AB only
O OO only
Genotype for Blood Type
I and i used in genotypeI used with A and Bi used with O
A and B are dominant over O: A and B are codominant
Ex: Genotype: AA is IAIA
Blood type chart
PHENOTYPE GENOTYPEA AA, IAIA
A AO, IAiB BB, IBIB
B BO, IBiAB AB, IAIB
O 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.
Cross: ii x IAIBIAi IAi
IBi IBi
ii
IA
IB
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:
– MOM: X X• Eggs all contain:
YX
X
or
XX XY
XX XY
X
X
X
Y
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 Heterozygous(carrier) Colorblind
Female: XX
Male: XY
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: Normal Male:• Female Carrier: Can a man be a carrier? • Female with hemophilia: Male with: