What Makes Us Unique?

People are almost identical to each other

Like all living creatures on Earth, humans are also the result of evolutionary development that has been going on for millions of years. The hereditary material that determines our development and appearance is transmitted from generation to generation – that is why most people have two legs and hands, five toes on each limb, a lung and a heart. These are just some of the basic properties which are common to all of us as two separate individuals actually share as much as 99.9% of the same hereditary material.

Statements like “like father, like son” are very much true as the genetic composition of an individual is a unique combination of the DNA material provided by both the mother and the father, and the numerous features and similarities of this composition are visible on the outside. Gregor Mendel discovered this as early as the 19th century, after having noted that biological differences are inherited from parent organisms as specific identifiable characteristics. For his research he used a pea plant, and demonstrated that the inheritance of certain traits of the plant follows particular patterns.

But we are still different

Genetic composition determines much more than just the structure of a pea plant, or the colour of our eyes and hair, as it has a significant impact on the development of the entire body and it arranges our response to environmental stimuli. After a more detailed examination we find that we are in fact very different – some eat vast amounts of food and never gain weight, others are exceptionally talented in certain sports, while others still drink a cup of coffee and spend a sleepless night. These and many other individual traits are largely a consequence of the differences within the remaining 0.1% of our hereditary notation.

Every cell contains DNA organized in chromosomes

People are unique creatures. We consist of a hundred and thousand billion cells that each contains DNA double helix carrying information for creating an organism. In each cell there are two copies of DNA: one from the father and the other from the mother. Each copy of DNA is arranged in super-bend structures, called chromosomes. In each cell we have 23 pairs of chromosomes. Exceptions are the gametes (eggs and semen) where we have only one copy of DNA; meaning only 23 chromosomes.

DNA is formed from a sequence of four different nucleotides
A molecule of DNA is composed of approximately three billion nucleotides. Each nucleotide consists of a phosphate group, pentose (monosaccharide with five carbon atoms) and a nitrogenous base. The individual nucleotides differ only in their nitrogenous bases. The human DNA contains four different nitrogenous bases and therefore four different nucleotides: cytosine (C), guanine (G), thymine (T) and adenine (A).
The specific sequence of nucleotides creates a gene
Imagine an incredibly long helix (three billion nucleotides) in which the sequence of the letters C, G, T, A is fixed. The individual sectors of this incredibly long helix (parts of the specific sequence of the letters C, G, T and A) carry the information for the creation of protein and consequently create genes. There are over 25 000 of these sectors, meaning that this is the precise number of genes we have.

Genes carry the information for the creation of protein

Protein is the foundation of the body. Also all the enzymes, the biological molecules which are the key to the proper operation of our organism are proteins by nature. Proteins are built from smaller molecules, named the amino acids. Genes actually carry the information which tells the amino acids how to create the corresponding sequence. The different amino acids in a specific sequence give rise to the corresponding protein.

Why We are Different?

Biologists use two fancy words to describe the relationship between your genes and your physical traits. The first word is genotype. Your genotype is your genes for a given trait. In most cases, you’ve got two copies of a gene – one from your mother and one from your father.

The second word is phenotype. Phenotype is what you actually turn out to be, the way these genes get expressed. Biologists have a saying involving these two fancy words: “Genotype determines phenotype.”

Let’s take eyelashes, for example. There are 2 kinds of eyelashes in people – long and short. Maybe you’ve got a short lashes version of a gene from your father, and a long lashes version of a gene from your mother. That’s your genotype. And what length of lashes do you actually have? Long – that’s your phenotype.

The eyelash example makes an important point. Some genes are dominant, and others are recessive. When you have two different genes for the same trait, and one is dominant (long lashes) while the other is recessive (short lashes), it’s the dominant trait that wins out in the phenotype.

But not all genes follow this dominant/recessive model. For example, the gene for blood type is codominant; if you get a gene for type A blood from one parent and type B blood from the other, neither dominates. Instead, you wind up with type AB blood.

Other human traits are polygenic, which means that they are controlled by several genes that contribute in an additive fashion. Skin color is believed to be polygenic. Scientists also think that polygenic inheritance is responsible for inherited predispositions to certain diseases, such as heart disease, arteriosclerosis, and some cancers.

Gregor Mendel was an Austrian monk who did extensive breeding research on pea plants. In doing so, he overturned our understanding of heredity.

At the time of Mendel’s work, in the 1860’s, most people believed in the blending theory of heredity, the idea that offspring were born with traits constituting a blend or average of the two parents. By this theory, when a red and a white flower are bred together, or crossed, their offspring should all be blended, that is, pink.

Mendel’s results suggested otherwise. For example, when he crossed pure-bred tall pea plants with pure-bred short pea plants, he got all tall pea plants-no blending there. He concluded that every organism possesses two “factors” (we now call them genes) for a given trait, and passes on just one of these factors-at random-to its offspring.

SNP makes us unique

Mutation in Latin means change. When we refer to mutation in genetics, we mean the change in the DNA sequence. This can occur in various ways: a nucleotide can be inserted into a sequence, another can be erased, and another still can be replaced by another one. The replacement of one nucleotide by another, which is then inherited by the descendants and kept within the population, is called the SNP. SNPs can cause a protein, encoded by a gene, to change, which means that its function will be changed as well. And even though people are identical in more the 99% of their hereditary notation, the SNPs (and some rare DNA mistakes) make everyone unique.

The SNP is inherited from parents and it determines the genotype

Sex cells, as opposed to body cells, contain only 23 chromosomes. Each parent gives their child 23 chromosomes, which means that the human body contains 46 chromosomes; therefore each of our body cells has two copies of a gene for each characteristic. When the gene copies are identical, they are referred to as homozygous, and when the copies are different, the person is a heterozygote. This gene state (homozygous or heterozygous) is the genotype. The gene copies are different when the nucleotide sequence differs in at least one site. For instance, a gene copy contains the A nucleotide in a specific location, while the other copy has the G nucleotide in the same place. We say that this person has two different alleles in the same location.

The genotype influences the phenotype

The two gene copies influence the final characteristic, the phenotype, together. One of great examples when we inherit lightly tanned skin from one of the parents, and a darker tone from the other, which makes our skin tone somewhere in between. Both body height and weight are also an evident example. The phenotype is the visible characteristic of an individual, like the above mentioned skin coloration or hair colour, or any other characteristic, like the predisposition to higher blood pressure or diabetes.