Blood Types & Codominance
Monday, April 1st, 2019
4/1 Warm-up: Punnett Practice
In dogs, tooth size is controlled by a dominant-recessive gene. Large teeth (T) is dominant to small teeth (t). If a homozygous recessive dog breeds with a heterozygous dog, what are the possible genotypes and phenotypes of their offspring? Use a punnett square to show your work.
In dogs, tooth size is controlled by a dominant-recessive gene. Large teeth (T) is dominant to small teeth (t). If a homozygous recessive dog breeds with a heterozygous dog, what are the possible genotypes and phenotypes of their offspring?
In dogs, tooth size is controlled by a dominant-recessive gene. Large teeth (T) is dominant to small teeth (t). If a homozygous recessive dog breeds with a heterozygous dog, what are the possible genotypes and phenotypes of their offspring?
Possible genotypes:
Possible phenotypes:
Today’s Agenda
Discussion:
What do you know about blood/blood type?
What is Blood?
What is Blood?
Blood Types
There are 8 different blood types, and a person’s blood type is determined by inheritance from parents.
Why are there Different Blood Types?
Red blood cells can have a carbohydrate attached to its surface that is called an antigen marker.
Antigens help the body know whether or not something is a foreign substance.
If our immune system encounters an antigen marker it has not seen before, it will attack that foreign substance.
Why are there Different Blood Types?
There are two types of antigens that can be on red blood cells: type A and type B.
Blood Types:
Type A → has A markers
Type B → has B markers
Type AB → has A and B markers
Type O → has no markers
Why is this important?
If you are blood type A, then you cannot get blood from anybody that has B markers.
The immune system will attack any red blood cell with an antigen marker it does not recognize.
If you are blood type A, your immune system will attack red blood cells with B markers, but not red blood cells with A markers.
Group Activity
Blood Donation
Because of the antigens we just learned about, only certain blood types can receive donations from certain other blood types.
Your goal is to correctly draw arrows from the donors to recipients.
Some blood types can donate to more than one blood type.
Percentage of Blood Types in the Human Population
Why does this system exist?
There is no benefits to having A markers over B markers or having markers at all.
Your blood type does not give you any advantages or disadvantages, it only determines who you can give blood to and who you can receive blood from.
Scientists believe that this system had some purpose in the past, maybe a certain antigen marker would make that human more resistant to a specific parasite, but whatever function it served in the past no longer exists today.
What about the + and - ?
In addition to blood cells potentially having a A and/or B antigen marker, red blood cells can also have a protein attached to its surface called a RhD antigen marker.
This system works the same as ABO discussed early.
Positive type: has RhD marker Negative type: no RhD marker (+) ( - )
Codominance
Page 151
The three types of inheritance
Remember this?
Incomplete Dominance
Simple Dominant-Recessive
Codominance
The genes for blood type are codominant.
This means that there are TWO dominant alleles and ONE recessive allele (a total of 3 alleles!)
The alleles:
A → dominant (IA)
B → dominant (IB)
O → recessive (i)
Notice that in AB Blood, BOTH dominant traits are expressed! (The blood cells have both antigen markers)
Blood Type & Genetics
The genotypes:
Punnett Squares & Blood Type
We can use punnett squares to find possible blood types that an offspring will have
Quick Practice (page 150)
We are going to do THREE practice problems together
150
Codominance Practice
Quick Practice
Draw a punnett square to show the cross between a mother with heterozygous A blood and a father with homozygous B blood.
Quick Practice
Draw a punnett square to show the cross between a mother with heterozygous A blood and a father with homozygous B blood.
Quick Practice
Draw a punnett square to show the cross between a mother with heterozygous B blood and a father with homozygous O blood.
Quick Practice
Draw a punnett square to show the cross between a mother with heterozygous B blood and a father with homozygous O blood.
Quick Practice
Draw a punnett square to show the cross between a mother with AB blood and a father with homozygous O blood.
Quick Practice
Draw a punnett square to show the cross between a mother with AB blood and a father with homozygous O blood.
Exit Question:
A child has a blood type of B. You know that the mother’s blood type is O. The person that believes he is the father of this child has a blood type of B.
Is this person the child’s father? Can you be absolutely sure? Show punnett squares (more than one if needed) to explain your answer.