Genes and genetics dictate all our traits. We result from the mix of our parents’ genes. Half of those genes are inherited from our mother, with the other half coming from our father. All the genes we have come in pairs, with one variant – or allele from one parent, and another allele from the other parent. These genes are responsible for all visible and invisible traits we have. However, not all alleles are equal, and there are cases in which one allele that determine a specific trait will block the expression of the other, a relationship called dominance.
Gene complete dominance
One of the common relationships between alleles of the same gene is complete dominance. What it means is that only one allele in the gene will express itself, with the other one – the recessive allele, being suppressed. While in some cases it is hard to determine the dominant relationship and which type of alleles we have, in some cases, the presence of a dominant allele expresses itself into a visible trait while having a recessive allele means that the trait is absent.
Examples of inheritance that show complete dominance
The photic sneeze reflex – or commonly known as the Achoo syndrome, is a dominant trait that causes people to uncontrollably sneeze when they are exposed to certain stimuli. One of the most common stimuli related to this trait is strong light. If you watch into the sun or a light bulb for a short amount of time and you suddenly start to sneeze uncontrollably, then you have the dominant allele in the gene that is mainly responsible for this trait.
The chin cleft is another physical trait that is related to a dominant allele. The usual prominent cleft to the chin is the result of a dominant gene that results in an incomplete fusion of the lower jaw bone or muscle halves in the embryonic or fetal development.
Eye color is yet another example of gene dominance. The allele responsible for the brown color is dominant over the blue allele, so if a gene has both of these, then only the brown trait will be expressed. While the mechanism of gene expression is complex and the genes involved in the expression of eye color are more than one, an oversimplified example of determining which allele you have is to compare your eye color with your parents. If they both have brown eyes and you have blue ones, then you have the recessive genes. If your eyes are brown, then you possess the dominant variant.
How many times have you been told that you have the eyes of your mother, or that you’re as tall and strong as your father? We all know that we inherit traits from our parents, but how exactly does that work? We still wonder why we may have blue eyes when both of our parents are brown-eyed, or why we tend to be susceptible to the same medical conditions as our parents. By learning some basics on genes and genetics, we can have a better understanding on how all this works.
Gene shuffling and inheritance
We inherit traits from our parents through genes. Genes are never single, as they come in sets of two versions called alleles. Each of our parents gives us half of their genes, or alleles. The combination of those two sets of alleles result in a unique mix that dictates your eye color, hair or height. The total amount of gene pairs is called a genotype, and it will determine the expression of every single gene, the total amount of traits being called a phenotype.
A gene is responsible for the expression of a trait, or contributes to a trait along with other genes. As mentioned earlier, genes come in pairs of alleles. The expression of the alleles may not be exactly the same. One example would be on the expression of eye color. There are alleles that trigger the expression of brown color, while others contribute to blue eyes. However, they don’t get expressed at the same time, as a person having both the brown and blue allele would have brown eyes.
This means that the brown allele is dominant, while the blue one is recessive. This applies to a wide range of genes and their respective traits. A dominant allele will always block the expression of a recessive allele, and the only way to have the recessive allele expressed is to have two of them in the same gene.
Explaining our traits
So all our traits result from the combination of alleles we inherit from our parents. While dominance is a common relationship between alleles from the same gene as expressed in the example above, there are many other types of dominance, such as incomplete or complete dominance, or co-dominance, where both alleles are expressed in the phenotype.
All these different combinations and relationships are the reason why we are unique, as we’re not copies of our parents, but unique mixes and expressions of numerous genes.
Genes are the basic building blocks of life. Every trait we have is determined by a gene or a set of genes. We inherit genes as units, with every child getting a copy of their parents’ genes. By studying genes and genetics we can not only understand how we inherit genes, but also how they express themselves into the numerous traits we have.
Genes and chromosomes
Genes are strings of DNA that contain information regarding every trait we have. Genes are found in the nucleus of every single living cell in our body. In the nucleus, they are contained inside structures called chromosomes, which represent super-coiled DNA and RNA strings coupled with proteins. When cells divide, chromosomes can be seen under the microscope, with all of them being X-shaped, except the Y-shaped male sex chromosomes.
Every human being has 23 pairs of chromosomes. Children inherit half of these, or 23 from the mother, while the other 23 come from the father. Each of these chromosomes can carry thousands of genes that determine every single trait, from eye color to height.
A human has 22 pairs of chromosomes that are common to both sexes, called autosomes, and one pair of sex chromosomes. Males have the sex chromosome pair composed of an X and a Y chromosome, while females have two X chromosomes. While all cells in the body have the 22 pairs of autosomes, the sex chromosomes are only contained by female eggs and male sperm cells.
Genes and inheritance
Every child inherits genes that are divided copies from their parents. The process of inheriting genes is similar to having two hands of cards which are first mixed, shuffled and then dealt out again. Although every human being has two copies of each gene, copies called alleles, only one allele is copied and included in the egg or sperm cells.
The egg and sperm cells combine, the uniting of the half set of genes resulting in a complete set. Although the child will have the same number of genes as his parents, every gene he has will be comprised of an allele inherited from the father, and one inherited from the mother.
The shuffling of genes results in a unique mix which explains why we are not only different than our parents, but different from each other. These genes determine all our physical characteristics while also influencing behavior and other traits such as intelligence.
There are many people who have many questions related to eye color inheritance. What determines their baby’s eye color? Why are there more colors than one, and what can they expect if the parents have a specific eye color. Since eye color is genetically inherited trait, we can understand it better by getting an insight into genes and genetics.
Eye color genetics
The eye color of a person is influenced by several genes. Genes make up the fundamental base for genetics. All genes come in pairs and they are called alleles. Each person has a pair of alleles, and babies inherit one allele from one parent, and one from the other. There are several genes that contain information about the eye color, information that will be expressed in the body depending on the relationship between them.
As mentioned before, genes come in pairs of alleles. However, not all alleles are equal. If we were to name alleles that determine brown eyes B and the ones determining blue eyes b, we would find that Bs are dominant over bs. That means that a person having a Bb gene would have brown eyes because B is dominant and will express over b, making b a recessive gene. The only way to have the b trait expressed is to have it paired with another b allele. So a person with a bb gene would have blue eyes, as both alleles are recessive and they both result in blue eye color.
Determining eye color
There have been many questions and disputes in the past regarding children who had blue eyes when both of their parents had brown eyes. Fortunately, genes and genetics can help us understand what happens and how eye color is determined. So as we mentioned earlier, B is dominant and b is recessive. A person with a gene composed of either BB or Bb alleles would have brown eyes, while a person with bb would have blue eyes. If two parents with brown eyes have Bb genes, then there’s a 25% chance of the baby getting the b allele from both parents, resulting in being born with blue eyes.
The above-mentioned examples represent an oversimplification of how genes influence our eyes. In reality, there are more genes that determine eye color, and the mechanism of gene expression is more complex. But by understanding how genes work, we can get insight into how they influence our body traits, and why we have some instead of others.