Codominance Worksheet Blood Types – Cracking the Code

Blood type is a bit of a conundrum unless you just so happen to be a biology student, doctor, and geneticist. No worries— we’re covering the gist of it today so you can walk away with a slightly more in-depth understanding of this complex but important topic.

Join us as we crack the code of codominance and blood types!

 

Blood Types – Codominance vs Dominance

What do we mean when we use terms such as codominance and dominance in regards to blood types? Does it suggest, like genetics, that some characteristics of our blood will supersede others and manifest accordingly?

Absolutely.

Your blood type is dictated by the presence of antigens on the surface of your red blood cells. These antigens are classified using the ABO blood group system, fittingly named A, B, or O.

Both the A allele and B allele are dominant, whereas the O allele is recessive. Therefore, receiving either an A or B allele from one parent and an O allele from the other will result in either A or B blood type respectively. For O, you will need both parents to pass down the O allele, as A and B exhibit dominance over O.

However, you can have one parent pass down an A allele and the other pass down a B allele. In this scenario, you have two dominant alleles vying for command and, thus, must settle for codominance. Your blood type, therefore, is AB, showing characteristics of both blood types.

 

Codominance Worksheet (Blood Types)

So, how do we work out what blood type we should expect using a worksheet?

Well, since it’s all based on the presence or absence of specific antigens, you’ll need to primarily look at this and secondarily keep in mind the Rh factor, which determines if your blood type is positive or negative.

Here’s a quick rundown:

• Type A: Has A antigens on the surface of red blood cells and anti-B antibodies in the plasma.
• Type B: Has B antigens on the surface of red blood cells and anti-A antibodies in the plasma.
• Type AB: Has both A and B antigens on the surface of red blood cells and no anti-A or anti-B antibodies in the plasma.
• Type O: Has no A or B antigens on the surface of red blood cells but has both anti-A and anti-B antibodies in the plasma.

 

What about the Rh factor? Again, a quick rundown is as follows:

• Rh-positive (Rh+): Has the Rh factor (D antigen) on the surface of red blood cells.
• Rh-negative (Rh-): Lacks the Rh factor on the surface of red blood cells.

 

Put it all together and you wind up with eight distinct blood types: A+, A-, B+, B-, AB+, AB-, O+, and O-.Each blood type has specific compatibility with blood transfusions and organ transplants, so each may provide some value in a medical setting.

 

Top 3 Blood Type Worksheets and Learning Material

 

1. ABO/Rh Blood Typing Learning Kit 

 

2. Medical Genetics 6th Edition

 

3. Genetics of Blood Type Experiment Kit 

 

Incomplete Dominance

Typically, one allele dominates the other, but, as discussed above, you have scenarios in which codominance can occur. Likewise, incomplete dominance occurs when neither allele totally takes over the set, resulting in a more unique phenotype.

Okay, let’s strip away the jargon and really explore this concept.

Imagine you have a plethora of paint colors, each unique in their own right. You’re painting a pretty picture, so you grab some red paint and mix in white to create pink. In color theory, that will totally work, but, in genetics, it’s not technically pink; it’s an intermediate shade of red and white.

It’s not correct to call it red, but it’s definitely not white. So, you now have a unique blend of both that creates something totally unique, and voila— that’s incomplete dominance in a nutshell.

 

Incomplete Dominance Punnett Square

Using our red-white example above, here’s what a Punnett square displaying incomplete dominance would look like.

	R	W
R	RR	RW
W	RW	WW

 

In this Punnett square, you can see that the heterozygous (RW) offspring display an intermediate phenotype, which, in this example, might represent pink due to incomplete dominance. Neither red, nor white, it is unique in and of itself.

 

Codominance Example

Let’s back it up to our discussion of codominance. Visually, that would appear as follows.

	A	B
A	A	AB
B	AB	B

 

Whereas the incomplete dominance Punnett square reveals a unique hybrid of red and white traits, the codominance displays distinctly A, B, or codominant AB depending on the traits of the parent.

 

Blood Type Punnett Square

The blood type Punnett square is basically a blood type chart that gives us insight on what traits, characteristics, and genetics the offspring of two parents may exhibit. Regarding blood types, it gives doctors, scientists, and researchers an idea of what may manifest given the traits of the parents.

 

The Rarest Blood Type of All

We know O positive is the most common blood type, but what is the rarest?

The answer: AB negative. Only a minute 1% of the population has AB negative blood, making it the rarest blood type by far.

Due to its rarity, individuals with AB negative blood are often considered universal plasma donors, as their plasma can be used for transfusions in individuals with various blood types.

 

How and Why Does Codominance Occur?

We know codominance occurs when two different dominant alleles, A and B, are both expressed in the phenotype of a heterozygous individual. So, neither A or B takes the reigns of the blood type or solely determines what characteristics may be exhibited.

Instead, A and B antigens both exist within the individual and, for that reason, the two work together without interference. Not A, not B, but something else entirely— AB.

 

How and Why Does Incomplete Dominance Occur?

When two characteristics blend together to form something entirely distinct, incomplete dominance occurs. In this scenario, one trait seems more present, but it is not pronounced enough to be considered a pure representation.

Pink snapdragons are an example of incomplete dominance in botany. In humans, wavy hair may be considered a characteristic in which neither straight nor curly hair genes are fully expressed.

 

Alleles Overview

We’ve used the term allele previously in our discussion, but what exactly are they?

Alleles are essentially different versions of a gene. In blood type morphology, that means A, B, and O. They determine more than just our blood type though. All of our traits, from eye color to our hair

Alleles come in pairs, one from each parent. They can be the same (homozygous) or different (heterozygous). If you inherit two of the same alleles, you have a homozygous genotype (like having two blue-eye alleles, BB). If you inherit different alleles, you have a heterozygous genotype (like having one blue-eye allele and one brown-eye allele, Bb).

The combination of alleles determines how traits show up in our bodies. So, in our example above regarding eye color, the homozygous blue-eyed offspring will unsurprisingly have blue eyes, whereas the heterozygous offspring will likely have brown eyes based on its dominance.

While codominance Worksheet blood types and variations can be complex, enough studying and examination can simplify the subject.

That said, it’s not impossible for them to have blue eyes. It’s just less likely.