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Why Do People Have Certain Genetic Traits?

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It's in Your Genes.
Has anyone ever said to you, "It's in your genes?” If so, they were probably referring to a physical characteristic, personality trait or talent that you share with other members of your family.

Despite sharing some characteristics with our peers and our family members, every one of us has a unique combination of traits.

We know that genes play an important role in shaping how we look and act and even whether we get sick. Some traits are controlled by genes passed from parent to child, others are acquired through learning but most are influenced by a combination of genes and environmental factors.

What Is a Gene?
To understand how genes work, let's review some biology basics.

Most cells have nuclei which contain 46 chromosomes. Chromosomes are tight packages of DNA which provide instructions to the body of how to function. DNA contains genes which are the smallest units of instructions. If you imagine your DNA as a cookbook, then your genes are the recipes that tell your cells how to function and what traits to express. Written in the DNA alphabet are four chemicals (adenine, thymine, cytosine, and guanine — called A, T, C, and G for short) which make pairs with each other to produce a double-stranded DNA (also called double-helix).

Each cell has 3 billion pairs of A, T, C, and G which are packaged into chromosomes with proteins called histones so tightly that DNA which is about six feet long, is able to be squeezed into very small cells only visible in microscope. Try to imagine how impossible this possible actually is.

Let’s take a closer look.
Below are some examples of variable traits that are easy to observe.

Inherited Human Traits

  • Earlobe attachment –
    • If earlobes hang free, they are detached. If they connect directly to the sides of the head, they are attached. Earlobe attachment is a continuous trait: while most earlobes can be neatly categorized as attached or unattached, some are in-between.
  • Tongue Rolling
    • Some people can curl up the sides of their tongue to form a tube shape. In 1940, Alfred Sturtevant observed that about 70% of people of European ancestry could roll their tongues and the remaining 30% could not.
  • Dimples
    • Dimples are small, natural indentations on the cheeks. They can appear on one or both sides and they often change with age.
    • Dimples are highly heritable, meaning that people who have dimples tend to have children with dimples—but not always. Because their inheritance isn't completely predictable, dimples are considered an “irregular” dominant trait.
  • Handedness
    • Handedness describes our preference for using either our left or right hand for activities such as writing and throwing a ball. Overall, about 10% of people are left-handed.
    • Multiple studies present evidence that handedness is controlled by many genes—at least 30 and as many as 100—each with a small effect; many are linked to brain development. Environment also plays an important role: some cultures actively discourage left-handedness.
  • Freckles
    • Freckles are small, concentrated spots of a skin pigment called melanin.
    • Freckles are controlled primarily by the MC1R gene. Freckles show a dominant inheritance pattern: parents who have freckles tend to have children with freckles.
    • Variations, also called alleles, of MC1R control freckle number. Other genes and the environment influence freckle size, color, and pattern. For example, sun exposure can temporarily cause more freckles to appear.

Know Your Genes.
Genes are the instructions for life as we know it. They affect your development before you're even born and play a role in everything from your appearance to your personality. Genes contain information about your heritage and your risk for certain diseases. Understanding your genes is part of understanding yourself, and you can use information about genetics to make decisions in your daily life. But remember, environment plays a crucial role in shaping the effects of our genes and its forces start working as early as the genes do, i.e. at conception.


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