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Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
Date: November 8, 2007
Drill
1. Brown eyes is dominant to blue eyes. My mother is heterozygous for this condition. My father has blue eyes, What percent
chance that I will have blue eyes? Complete the Punnett Square and include the genotypic ratio and percents and the
phenotypic ratio and percents.
Write your own Question
You have been supplied with traits, which exhibit dominance and recessive characteristics. Write you own question about your pets,
family or imaginary friends. It will be completed by another person so make it legible and clear exactly what you mean.
Incomplete Dominance
Incomplete dominance
When you cross the two you get a blending of the two traits. Both possibilities are show with a capital lettr because both
are dominant.
I have a red and white snapdragon. When I cross them with one another, what are the phenotypic and genotypic
percents and ratios?
In Smurfs big ears is incompletely dominant to small ears. If a small eared and a large eared Smurfs have children
what are the chances they will have small ears?
Incomplete Dominance
Incomplete dominance is basically just a blending of traits--the heterozygous form is a blend of the homozygous dominant and the homozygous
recessive . In the example below, a red flower ( genotype RR) is crossed with a white flower (genotype R'R'). The succeeding F1 generation
contains all pink flowers (genotype RR'), because neither R nor R' is truly dominant over the other allele. When this generation is allowed to selfpollinate, a ratio of one red flower (RR) to two pink flowers (RR') to one white flower (R'R'), (1:2:1) is obvious. This shows, as Mendel had
determined, that the alleles remain unaltered, since the red and white phenotype has reappeared. Please see the diagram below to illustrate this:
http://library.thinkquest.org/18258/geneint1.htm
a. Blending of traits
i. R=red
ii. R1
iii. RR =Red
iv. R1 R1=white
v. RR x R1 R1
R R1 = 100% Pink & 100% R R1
Incomplete Dominance
*
*
*
(or an
In some cases, an intermediate phenotype is shown
Neither allele is dominant
In snapdragons, flower color can be red, pink, or white. The heterozygous condition results in pink flowers
intermediate trait)
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
*
A white snapdragon crossed with a red snapdragon produces all pink offspring
*
Two pinks crossed together produce 1/4 white, 2/4 pink, and 1/4 red
When dealing with incomplete dominance and codominance it does not matter what letter you use, as long as the
heterozygous condition always denotes the intermediate trait. In the diagram R is used, but you could also use W or
even P. Ww = pink, Pp = pink if these letters are used.
http://www.biologycorner.com/bio4/notes/beyond_mendel.php
In Smurfs, big ears are incomplete dominant to small ears. If a small eared and a large eared Smurf have children, what
are the chances they will have small? Do the Punnett Square to prove it.
B=Big Ears
S=Small Ears
B
B
S
BS
BS
S
BS
BS
100% medium ears
Genotype- 4 BS
Phenotype- 4 medium
Co- Dominance
When crossed both are exhibited. Shown with a capital letter
Black hair is co-dominance with red hair horses. If I cross a black horse with a black and red horse, what are the
chances of getting a black horse?
Show the Punnett Square
Green skin is co-dominant with yellow skin in frogs. If I cross a homozygous yellow frog with a heterozygous frog, what
is the phenotypic percents and ratio’s for the cross? Show the Punnett Square.
B. Co-dominance
a. NOT A BLEND
b. Both traits are shown
B-Brown
W-white
BB X WW
W
W
B
BW
BW
B
BW
BW
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
Codominance
*
Both alleles can be expressed
*
For example, red cows crossed with white will generate roan cows. Roan refers to cows that have red coats
with white blotches.
*
This phenotype might seem to support the blending theory. (The blending theory predicts pink F1 progeny.)
*
The F2 progeny, however, demonstrate Mendelian genetics. When the F1 roan individuals self-fertilize, the
F2 progeny have a phenotypic ratio of 1 red:2 roan:1 white.
*
This mode of inheritance is called incomplete dominance.
*
The phenotypic outcomes for cow color and incomplete dominance in general can be explained
biochemically.
*
One allele of the gene codes for an enzyme that functions in the production of the red color. The other allele
codes for the gene to make white color. If both alleles are present, both are expressed, resulting in a cow that has
some red and some white.
*
MendelÕs laws are not compromised here, he just happened to find in peas examples of complete
dominance only.
http://www.biologycorner.com/bio4/notes/beyond_mendel.php
Geno %= 100% BW
Ration all BW
Pheno% 100% Brown & white
Ratio All Brown & White
Codominance is an interesting case were there is no real dominant or recessive allele. Instead, both alleles are fully expressed in the
heterozygous form (the homozygous forms act normally).
A good example of codominance is a person's blood type. A person with blood type AB is showing the results of having both the IA and IB
codominant genes. The AB blood type expresses the characteristics of both blood types A and B; therefore, the alleles for blood type must be
codominant. http://library.thinkquest.org/18258/geneint1.htm
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
http://www.uic.edu/classes/bios/bios101/genes1/sld022.htm
Blood Types:
Everybody has a blood type. The most common blood type classification system is the ABO (say "A-B-O") system
discovered by Karl Landsteiner in the early 1900s. There are four types of blood in the ABO system: A, B, AB, and
O. Your blood type is established before you are born, by specific genes inherited from your parents. You receive
one gene from your mother and one from your father; these two combine to establish your blood type. These two
genes determine your blood type by causing proteins called agglutinogens (a-GLOO-tin-a-gins) to exist on the
surface of all of your red blood cells.
There are three alleles or versions of the blood type gene: A, B, and O. Since everybody has two copies of these
genes, there are six possible combinations; AA, BB, OO, AB, AO, and BO. In genetic terms, these combinations are
called genotypes, and they describe the genes you got from your parents.
http://learn.genetics.utah.edu/units/basics/blood/types.cfm
Overall, type O blood is the most common blood type in the world.[21] Type A blood is more prevalent in
Central and Eastern Europe countries.[21] Type B blood is most prevalent in Chinese/Asian communities when
compared to other races.[21] Type AB blood is easier to find in Japan, China and Pakistan.[21]
In some ways, every person's blood is the same. But, when analyzed under a microscope, distinct differences are
visible. In the early 20th century, an Austrian scientist named Karl Landsteiner classified blood according to those
differences. He was awarded the Nobel Prize for his achievements.
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
Landsteiner observed two distinct chemical molecules present on the surface of the red blood cells. He labeled one
molecule "A" and the other molecule "B." If the red blood cell had only "A" molecules on it, that blood was called type A.
If the red blood cell had only "B" molecules on it, that blood was called type B. If the red blood cell had a mixture of both
molecules, that blood was called type AB. If the red blood cell had neither molecule, that blood was called type O.
If two different blood types are mixed together, the blood cells may begin to clump together in the blood vessels,
causing a potentially fatal situation. Therefore, it is important that blood types be matched before blood transfusions
take place. In an emergency, type O blood can be given because it is most likely to be accepted by all blood types.
However, there is still a risk involved.
A person with type A blood can donate blood to a person with type A or type AB. A person with type B blood can donate
blood to a person with type B or type AB. A person with type AB blood can donate blood to a person with type AB only.
A person with type O blood can donate to anyone.
A person with type A blood can receive blood from a person with type A or type O. A person with type B blood can
receive blood from a person with type B or type O. A person with type AB blood can receive blood from anyone. A
person with type O blood can receive blood from a person with type O.
Because of these patterns, a person with type O blood is said to be a universal donor. A person with type AB blood is
said to be a universal receiver. In general, however, it is still best to mix blood of matching types and Rh factors.
http://sln.fi.edu/biosci/blood/types.html
Red blood cell compatibility table[26][27]
Recipient blood
type
Donor red blood cells must be:
AB+
O- O+ A- A+ B- B+ AB- AB+
AB-
O-
A+
O- O+ A- A+
A-
O-
A-
A-
B-
AB-
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
B+
O- O+
B- B+
B-
O-
B-
O+
O- O+
O-
O-