A lot of people wonder why they look the way they look. Perhaps they are different from their parents, their relatives, or the opposite of what has been recorded in their family. Some wonder how they become a higher version of what is recorded in their lineage. Sometimes, people look like their great-grand, grandparents, or even uncles. Many live in wonder as to why they look the way they look. Inappropriate exposure to knowledge has made many attribute the cause to spirituality and chance, and some attribute it to relativity without knowing the actual phenomenon behind it.

Now, for reproduction to take place in humans, the gamete (sperm) from the male sex organ called penis, has to meet the egg released by the female during her ovulation.  The sperm and the egg are haploids, this implies that they have one set of chromosomes. Chromosomes are the structures that house the DNA (deoxyribonucleic acid). DNA is seen as the biological material that contains genes and transmits them across generations. On meeting, these two entities (the sperm and the egg) fuse to form a diploid cell known as the zygote. Before this processes occur, millions of sperm cells go on this journey. But only a single sperm penetrates to fertilize the egg. If more than one should fertilize an egg, it leads to a condition known as polyspermy. This condition could be lethal resulting from the excessive presence of centrosomes which may impair the development of the zygote.

It is necessary to understand that during fertilization, sperm can fertilize an egg into a male or female individual. To understand how this is achieved, we must know the human chromosomes, especially the sex chromosomes.


The human genome consists of 23 pairs of chromosomes, with each chromosome consisting of a single long molecule of DNA. Each chromosome contains a single DNA, which contains millions of base pairs that are translated to proteins. Chromosomes consist of the genetic information called genes, that make you who you are, including your physical traits, your risk of developing certain diseases, and more. The first to the twenty-second pair of chromosomes are autosomes whereas the twenty-third chromosome is the sex chromosome. This suggests that a person’s sex is determined by their chromosome.

The X and Y chromosomes are the two sex chromosomes found in humans. Males possess a single copy of the X chromosome along with a copy of the chromosome known as the Y chromosome, whereas females possess a pair of copies of the X chromosome. The X chromosome is considered the “default” chromosome, while the Y chromosome carries the genes that determine maleness. The SRY (sex-determining region Y) gene is one example of such a gene; it initiates the formation of male reproductive organs after fertilization. In addition to determining sex, the X and Y chromosomes carry other genes that influence height eye color, and other physical traits. They also play a role in the formation of some ailments like color blindness and Turner syndrome.


In human genetics, genes occur in pairs but exist in different forms called alleles. Some alleles are dominant, meaning that they dominate, while others are recessive. The dominant allele is always represented with the upper case while the lower-case letter represents the recessive allele. A dominant allele is expressed provided it is present in the gene, even when only one copy of the allele is present. For example, the dominant allele for brown eyes will be expressed, even if the person has one copy of the recessive allele for blue eyes (heterozygous state). A recessive allele is only expressed when both copies of the allele are present in the gene (homozygous state).

After birth, an individual has traits that are associated with him or her. Those traits or characters that are fully influenced by genes are called qualitative traits while the ones with gene and environmental influence are called quantitative traits. Qualitative traits may have little or no environmental influence because they are not controlled by many genes. Examples are sex, albinism, etc. Conversely, the quantitative traits are controlled by many genes with great influence by the environment. Examples include height, size, etc.


  1. Gene

Genes code instruction for people’s expression. It is found in the chromosome, and they are different for every human. That is why no two individuals are the same.  For each gene, two alleles are either the same (TT or tt as in the gene for height where T represents tall and t for short) or different (Tt). Now, traits that are not seen in a particular generation may still be seen in subsequent generations. It could be because the gene for the trait is recessive and could have been masked by the dominant allele as earlier explained. As seen in Tt, the carrier is tall but has the allele for shortness which can only be expressed when the gene is in the homozygous recessive state (tt). Therefore, an individual who has Tt is a carrier for shortness. If the individual is married to another with Tt for height, this implies that both of them are tall. There is a probability that they will give birth to a child with genotype tt for height. By implication, the child will be short. The shortness expressed is not seen in the parents and this could raise a misunderstanding on why the occurrence. The knowledge of the gene and its operation will help quench the taste for interrogation. If a trait is not seen in the present generation, the population of the generation could be carriers of the trait. By implication, during reproduction, the right combination of alleles could be produced for the trait to appear in subsequent generations.

  1. Environment

After fertilization, the production of allele combinations for all traits, development, and growth proceeds. Then, the environment will start showing an influence on the expressions given by the gene. The environment is those things that affect the living organism. They could be living (humans, animals, plants, etc.) or non-living (X-ray, smoke, sun, food, etc.). The environmental factors act on expressions given by the gene, thereby, modifying it to give different or related expressions.


  • Nutrition: The most established environmental factor that influences an individual’s appearance is nutrition. A person’s diet can affect height, weight, health, skin, hair, etc. For example, a meal that is rich in processed foods and sugar can lead to obesity, while a diet rich in fruits and vegetables can lead to a healthy body weight and better overall health. In addition, consumption of food that lacks certain nutrients, such as vitamin D, can result in a higher risk of rickets. Ricket is a condition that is associated with weak and deformed bones. Therefore, nutrition plays a major role in shaping an individual’s appearance.
  • Stress: Stress includes heat, temperature, and pressure stress. It impacts also an individual’s appearance. When a person is under stress, his or her body produces a cortisol hormone. Cortisol hormone can alter physical changes, which range from increased acne, and thinning of hair, to decreased skin pigmentation. In addition, stress can cause an individual to lose weight, or gain weight. To gain weight, cortisol increases appetite, leading to overeating. Furthermore, stress decreases the quality of sleep, hence, affecting the health of the victim.
  •  Chemical exposure: Exposure to chemicals such as lead and mercury, can influence the appearance of an individual. For example, lead exposure can induce hair loss and changes in the colour of the hair, skin, and nails. A similar report is given for mercury, as well as a discoloration of the teeth.
  • Drugs and Cosmetics:  As seen in some drugs and cosmetics, which can affect the physical appearance. Drugs like Accutane are used to treat acne, but they can induce dryness and peeling of the skin. Based on the record, some acne medications can increase skin’s sensitivity to sunlight, leading to suntan. Makeup cosmetics affect appearance.
  1. Mutation.

Mutation is an identified change in the genome of a living organism. This can also lead to changes in the physical features of someone; this is because the gene gives expression of whatever it encodes. When the codes change, it will still express the new code. Due to mutation, codes that have not existed before could be produced, hence, giving rise to new traits that have never existed. Agents of mutation are called mutagens. Examples of mutagens are cigarette smoke, radiation (an example is X-ray), drugs, chemicals, electric charges, etc.

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