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Author Topic: [Biology 9] Human Genetics - Types Of Genotype & Blood Group  (Read 1139 times)

Offline Mr. Babatunde

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Genotype is an organism's genetic make-up and it results in some of the organism's physical characteristics. It is the mixture of alleles situated on corresponding chromosomes that distinguishes a particular characteristic of an organism.

You may simply state that genotype is an inherited trait, and genotype is determined by genetic knowledge passed down by the parents to their offspring. The set of genes in human DNA responsible for a specific phenotype may also be considered.

Your genotype is your total heritable genetic identity; private genome sequencing will show it to be your special genome. The word genotype, however, can be compared to a specific gene or collection of genes carried by an organism.

For instance, if you carry a diabetes-related mutation, without taking into account all the other gene variants that you may carry, you may refer to your genotype only with regard to this mutation.

Genotypes can only be determined by biological tests, not observations. The entire genetic information about an organism is contained in a genotype  even those characteristics which are not expressed visually.

Genotype helps to determine which characteristics an individual will express, for example: whether they have freckles or not, if they are lactose intolerant, if they have hair on their knuckles or if their eyes will be blue, brown or another colour.

How Genotypes Come About?

Genes are found on chromosomes, those tightly-packed DNA structures in the cell nucleus. In sexually-reproducing organisms, chromosomes come in pairs, one from the mother and one from the father. For example, each person will have two ‘Chromosome 1s’ and ‘Chromosome 2s’.

Chromosomes in a pair (except sex chromosomes) are called homologous chromosomes because they contain the same genes. For example, both chromosome 8s contain, among many others, the gene that determines whether or not a hairline forms a widow’s peak.’

There are always two copies of each gene present, one from each parent. A gene can have different versions, called alleles. Alleles are various versions of a gene and the combination of alleles inherited from the parents is what gives rise to genotypes.

Examples Of Genotype
examples of genotype are the genes responsible for the following listed below

  • eye colour
  • hair colour
  • height
  • how your voice sounds
  • certain diseases
  • certain behaviors
  • the size of a bird’s beak
  • the length of a fox’s tail
  • the colour of stripes on a cat
  • the spots on a dog’s back
  • a person’s shoe size

Eye Colour

Although a particular genotype consists of many nucleic acids, scientists typically represent genotypes with single letters, or two letters in the case of sexually reproducing organisms that receive one allele from each parent.

For example, the trait for eye colour could be represented with the letter “E”. Varieties, or alleles, of that trait that are dominant will be designated by capital letters. Therefore, “E” will represent brown eyes. Traits that are recessive are written in lower case. The allele for blue eyes is recessive to the allele for brown eyes, so we can call it “e”.

Some set of parents has brown eyes. Having brown eyes only tells us their phenotype, not their genotype. The parents could be “Ee”, “EE”, or there could be one of both. A single “E” allele in the genotype will result in the brown-eyed phenotype, even if the parent harbours a recessive “e” allele as well.

The parents conceive a child. The child has blue eye. This tells us that the child is homozygous recessive, or “ee”, because only two recessive alleles can produce blue eyes. This also tells us a lot about the parents.

The baby, having two “e” alleles, got one from each parent. Therefore, each parent has one “e” allele to give, while having the brown eyed phenotype. This shows us that the parents have the heterozygous “Ee” genotype. If either parent where homozygous dominant, “EE”, the baby would have received at least one dominant “E” allele, giving it brown eyes.


Cystic Fibrosis

For a long time, it was not known why some children would develop a thick mucus in their airways, causing them to be short of breath and wheezy. The children had a variety of other symptoms, such as the inability to process food efficiently, gas, and weight loss. Until recent advances in medical and genetic sciences, many children died at a very early age.

After years of research, cystic fibrosis was found to be caused by a defect in a gene that produces salt channels across cell membranes. These salt, or ion-channels, are used to maintain pH levels in various cells, remove waste, and remove nutrients from the intestines.

The genotype of people with cystic fibrosis is homozygous recessive. In other words, they carry two copies of the non-functioning allele for the gene that creates specific ion channels. Some people, known as “carriers” can have a functioning, normal phenotype, while having a heterozygous genotype. This means that a carrier can pass a non-functioning allele on to their child. Unknowingly, two carriers can both pass on the non-functioning allele, and the child will receive a non-functioning homozygous recessive genotype.

However, if one or both carrier parents passes on their good allele, the child will not have the symptoms of cystic fibrosis. If the child receives one functioning and one non-functioning allele, they will be a carrier as well. The child will not be a carrier if they receive two functional alleles.

If parents who are both carriers, the genotypic ratio of offspring will be set at 1 normal: 2 carriers: 1 cystic fibrosis genotype. This genotypic ratio can be counted in a Punnett square. Place the heterozygous parents on the sides of the square, separating their individual alleles (Aa and Aa below).

Then, simply fill in the boxes with the two alleles that would be received by each potential child. It can quickly be seen by counting that the genotypic ratio is 1AA:2Aa:1aa. In this case the phenotypic ratio would be 3 normal: 1 cystic fibrosis

Types Of Genotype

There are four (4) different types of  hemoglobin genotypes (hemoglobin pairs/formations) in humans:




• GENOTYPE AC (Uncommon)

SS Genotype and AC  Genotype are the abnormal genotypes or the sickle cells. We all have a specific pair of these hemoglobin in our blood which we inherited from both parents.


Genotype AA has the uttermost advantage when it comes to choosing a partner for copulation and reproduction, people with genotype AA can reproduce with any other genotypes without having the fear of producing offspring with the sickle cell disease.

People with Genotype AS are at great disadvantage when they want to choose who to reproduce/copulate with, the reason why is because they are sickle cell carriers and can only copulate with genotype AA alone. This is to Avoid them to have offspring’s who will carry the dreaded disadvantaged sickle cell disease.

Individual with Genotype AC are also at greater disadvantage when it comes to choosing a life partner because they have the traits of sickle Cell Anemia (SS).

Genotype SS take the saving grace of God for them to be able to copulate/reproduce with other Genotype apart from AA genotype. People with genotype SS are set of individuals with Sickle cell disease.

Sickle cell anemia also known as sickle cell disease is caused by a gene mutation of the red blood cells whereby these blood cells are shaped like a crescent-shaped moon. The sickle cell gene is inherited so to have the disease you must inherit the genes from both parents. Children with only one copy of the gene are said to have sickle cell traits.

Types Of Sickle Cell Disease

There are four common types of sickle cell disease

1. Hemoglobin SS: This is the most common type of sickle cell, and it occurs when a child inherits copies of the hemoglobin S gene from both parents.

2. Hemoglobin SC disease is another common type of sickle cell and it occurs when a child inherits the hemoglobin C gene from one parent and hemoglobin S gene from the other parent.

3. Hemoglobin SB+ thalassemia This disease affects beta-globin gene production which results in the production of less beta protein which causes a reduction in the size of red blood cells.

4. Hemoglobin SB 0 thalassemia It is the least common sickle cell, and it involves the beta-globin gene.


Other rare types of sickle cell anemia with less severe symptoms include hemoglobin SO, hemoglobin SE, and hemoglobin SD.

Why it is Important to Know Your Genotype

Knowing one’s hemoglobin genotype before choosing a life partner is important because there may be compatibility issues which could have devastating effects when it comes to conception.

Individuals with sickle cells experience severe pains in body parts where oxygen flow is compromised due to blockage in the blood vessels. Therefore, AA can marry anybody
AS is better off with AA, AS and AS, AS and AC are too risky and two sickle cells should avoid conception

Genotype Compatibility Chart

The information below is the compatibility chart of genotypes and how it influence our way of life. Study this table below carefully:

AA + AA = AA, AA, AA, AA (Excellent)
AA + AS = AA, AS, AA, AS, (Good)
AA + SS = AS, AS, AS, AS, (Fair)
AA + AC = AA, AA, AA, AC. (Good)
AS + AS = AA, AS, AS, SS, (Very Bad)
AS + SS = AS, SS, SS, SS, (Very Bad)
AS + AC = AA,  AC, AS,SS. (Bad; Advice needed)
SS + SS = SS, SS, SS, SS, (Very Bad)
AC + SS = AS, AS, SS, SS, (Very Bad)
AC + AC = AA, AC, AC, SS. ( Bad; Advice needed)


The best compatibility is when AA marries an AA. That way they will be able save their future children the worry about genotype compatibility.

When AA marries an AS, they will end up with kids with AA and AS which is good. But sometimes if they are not lucky enough all their kids may be AS which limits their choice of partner.

It is advisable for AS and AS not to marry because there is every chance of having a child with SS.

It is highly sagacious for AS and AC to marry each other because they are both Sickle cell carrier and it will be very risky if they do.

It is disastrous for AS and SS  to marry because they can produce anything less than SS and AS. Therefore, they shouldn’t think of marrying.

And definitely, SS and SS must not marry since there is absolutely no chance of escaping having a child with the sickle cell disease.

cross breading gynotype

What is Blood Group?

Red blood cells transport oxygen in the body. It’s this same red blood cells that have antigens and Rhesus factor that determine a person’s blood group. The differences in blood groups are due to the presence or absence of antigens and antibodies.

While antigens are located on the surface of the red blood cells, antibodies are in the blood plasma. Did you know that there is more than 30 genetic blood group system? And Out of these 30, only the Rh and the ABO system are considered during a blood transfusion.

blood group donor

Furthermore, in the ABO blood system, not all blood groups are compatible. When incompatible blood groups are mixed during a blood transfusion, it results in agglutination. Therefore, before a blood transfusion is carried out, a medical practitioner has to do a cross-matching which is generally the process of determining whether the blood of a donor is compatible with the receiver.

When the RBC carry an antigen a, an individual is said to have blood type A. If the RBC carry antigen b, then the expected blood type is also B. However, when the blood cells have both a and b antigens, then the person has blood group AB. On the other hand, when your blood cells lack any antigen, then your blood type is O.

blood groups

People with blood group O are considered universal donors which means that they can donate blood to all blood groups.

AB+ are universal blood recipients which means that they can receive blood from all blood groups.

AB- people can receive blood from those with A-, B-, AB- and O-.

A+ can receive blood from A+, O+, A- and O-.

A- can receive blood from A- and O-.

People with B+ blood types can receive blood donations from those with B+, O+, B- and O-.

Individuals with blood group B- can receive blood from only two groups: B- and O-. If your blood type is O+, you can receive blood from those with O- and O+ blood groups.

O- can only receive blood from O-.

Here is a summary of the types of genotype and blood group including the antigen and antibody that each blood group has. Blood type B Can either have genotype BB or BO, as the antibodies in the plasma and B as the antigens on red blood cells.

Blood type A Has genotype AA or AO, antigens on the red blood cells are A and b antibodies in blood plasma. Blood type AB Blood group AB has genotype AB, antigens A, and B, no antibodies, Blood type O Has genotype OO, no antigens on red blood cells but has both antibodies a and b.

Why It Is Crucial To Know Your Blood Group

It is important to know your blood type should in case you need a blood transfusion or you want to donate blood to someone. It is also necessary because it plays a role in determining paternity. Before a blood transfusion takes place it must be established that the donor’s blood type is compatible with the recipient’s blood type.

The combination of certain antibodies (proteins protecting the body) can be harmful or even lead to fatal symptoms if antibodies perceive foreign cells as a threat. It is our immune systems’ way of protecting us.

Comparison Between Genotype and Phenotype

Genotype and phenotype are related words that are very similar-sounding, but actually mean different things. The Genotype is the collection of genes responsible for a specific feature in our DNA. Whereas the physical manifestation, or features, of that trait is the phenotype.

For instance, it is said that two species that have even the slightest variation in their genes have different genotypes. These two mice may have different genotypes, even if they share the same phenotype of white fur, both may still be white.


Phenotype is what you see, the apparent or detectable expression of gene outcomes, coupled with the effect of the environment on the appearance or actions of an organism. For instance: the expression of gene information that can be detected through the senses (such as the sound of the chirping of a bird or the color of the hair of a cat).

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