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DNA, Gene, Chromosome and Genome – What is the Difference?

DNA, Gene, Chromosome and Genome – What is the Difference?

  • DNA:

It is a double helix structure. It has sugar phosphate backbone and it is made up of four nucleotides A, T, G and C.

In humans, the DNA is about 2 meters long and this much long DNA needs to fit in our tiny nucleus which is around 5-10 µm in size. So in order to fit inside the nucleus; DNA has a packaging strategy where it undergoes coiling by formation of nucleosome.

Figure 1. DNA

  • Gene:

In our 2 meters long DNA, there are segments or chunks of DNA i.e. specific nucleotide sequences around 100s of bp long which codes for specific proteins and RNA. These segments of coding DNA is called gene and we have about 20,000 genes spread across all the chromosomes.

Every gene has a specific site in our DNA. For example, cystic fibrosis gene is present on chromosome 7. The traits that we get from our parents is because of the genes that we get from them so traits passes from parents to child in the form of genes.

Figure 2. Gene

  • Chromosome:

As we just saw above that the DNA is too long to fit inside the nucleus. So it undergoes packing mechanism where the DNA starts wrapping itself around the histones proteins. This assembly where DNA is wrapped around histones is called nucleosome. Nucleosome formation condenses the DNA and therefore the space it requires to fit inside a nucleus would reduce. These nucleosomes would further undergo condensation by arranging them self in coiled form called chromosome.

So chromosome is nothing but super condensed form of DNA where it is wrapped around histone proteins. In humans, there are total of 46 chromosomes. We are diploid so that means 23 chromosomes comes from mother and 23 chromosomes comes from father; giving us total of 46 chromosomes or 23 pairs of chromosomes.

As saw above that DNA is about 2 meters long so when you take all the 46 chromosomes, unwind them and put them in one stretch that makes the 2 meters long DNA.

Figure 3. Chromosome

  • Genome:

A genome is organism’s complete set of DNA. This means the entire DNA present in a cell and for humans other than nuclear DNA; there is also DNA in mitochondria so it is all the nuclear DNA distributed over 24 chromosomes (22 autosomes and 2 sex chromosomes) and DNA in mitochondria. For example, if we are talking about plants we will take chloroplast DNA in consideration.

Since we are diploid, we have two copies of genome in nucleus because we have all the chromosomes in pair.

So when we put together all the genetic information present inside a cell; it becomes the genome of an organism.

So think of it this way that genome is huge book carrying lot of information and for easy access to this information; nature has divided it into 24 chapters (22 autosomes + 2 sex chromosomes). So genome is divided into 24 chromosomes.

Figure 4. Summary

I hope this helps 🙂

Watch a video on this topic here.

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Blood Compatibility and Plasma Compatibility – What is the Difference?

Blood Compatibility and Plasma Compatibility – What is the Difference?

To understand the compatibility, it is important that we know the bases of ABO blood grouping system. It is based on the presence of specific antigen on red blood cells of an individual.

Table 1 shows the antigens present on red blood cells and antibodies presents in plasma for each blood group.

Table 1. Antigens and Antibodies Present for Each Blood Group

Blood Group Ag Present on RBC ABO Abs Present in Plasma
O No Ag Anti A and anti B
A Ag A Anti B
B Ag B Anti A
AB Ag A and Ag B No Abs
Rh+ Rh D No Abs
Rh- No Ag No Abs

In case of Rh + or Rh– there will be no Abs present naturally in plasma because Rh Abs are developed only after an individual is exposed to Rh D antigen.

Now based on this we can differentiate the compatibility for red blood cell type and plasma type. Keep the above table as reference to understand the compatibility.

During transfusion it is preferable for a patient to receive blood and plasma of the same ABO and RhD group but if the required type is not available based on compatibility they may be given alternative type as shown in table 2.

Table 2. Blood Compatibility and Plasma Compatibility for Each Blood Group

Recipient Blood Type Donor RBC Donor Whole Blood

(RBC + Plasma)

 Donor Plasma
A+ A+, A-, O+, O- A+ A- A+, A-, AB+, AB-
A- A-, O- A- A+, A-, AB+, AB-
B+ B+, B-, O+, O- B+, B- B+, B-, AB+, AB-
B- B-, O- B- B+, B-, AB+, AB-
O+ O+, O- O+, O- A+, A-, B+, B-, O+, O-, AB+, AB-
O- O- O- A+, A-, B+, B-, O+, O-, AB+, AB-
AB+ A+, A-, B+, B-, O+, O-, AB+, AB- AB+, AB- AB+, AB-
AB- AB-, A-, B-, O- AB- AB+, AB-

When it comes to blood transfusion, it can be either only red cells or blood as a whole. So if we are talking about RBC, we need to consider only Ags from donor but when we are talking about whole blood since it has both RBC and plasma we need to consider both Ags and Abs from donor. In case of plasma we need to consider only Abs from donor because plasma doesn’t have RBC and so no Ags.

As shown in table 2, plasma from blood group AB can be given to blood group O. But when it comes to blood as a whole because of present of Ags on RBC, O type cannot accept red blood cells or blood as whole from any other blood type other than blood group O.

Blood group A and B type individuals can accept plasma from AB individuals because blood group AB type will not have any Abs in their plasma.

Blood group AB type can accept plasma from only AB type because it is the only plasma without anti A and anti B Abs in it.

Rh- individual can accept plasma from Rh+ individual because there are no anti Rh antibodies present naturally in plasma.

In blood transfusion and to be specific for red cell transfusion, AB is universal acceptor and O is universal donor.

But in plasma transfusion, AB is universal donor and O is universal acceptor.

I hope this helps 🙂

Watch a video on this topic here.