Overview
What is DNA? - DNA carries your genetic code
Your body contains 50 trillion tiny cells, and almost every one of them contains the complete set of instructions for making you. These instructions are encoded in your DNA. DNA is a long, ladder-shaped
molecule. Each rung on the ladder is made up of a pair of interlocking units, called bases that are designated by the four letters in the DNA alphabet - A, T, G and C. The letters made words. The words make sentences. These “sentences” are called Genes. Each gene is like a ‘recipe’ for making a certain protein with a specific function in the body.
What is a chromosome? - DNA is packaged into chromosomes
Each cell in our body contains a lot of DNA. In fact, if you pulled the DNA from a single human cell and stretched it out, it would be three meters long! The DNA is packaged into compact units called
“chromosomes”. Humans have 23 pairs of chromosomes in almost every cell in the body. Each parent contributes one chromosome to each pair, so you get half your chromosomes from your mother and half from your father. We inherit one sex chromosome from each parent. Typically females have two X chromosomes and males have an X and a Y. Mothers always pass an X chromosome on to their children. Whether your father passes on his X chromosome (leading to a pair of X chromosomes) or his Y chromosome (making a mixed set) determines your sex.
What is a Gene? - Chromosomes carry genes
Chromosomes are further organized into short segments of DNA called genes. If you imagine your DNA as a cookbook, then your genes are the recipes. Written in the DNA alphabet - A, T, C, and G - the recipes tell your
cells how to function and what traits to express. For example, blood contains red blood called that transport oxygen around our bodies. The cells use a protein called “hemoglobin” to capture and carry the oxygen. Of our 25,000 genes, only a few contain the instruction for making hemoglobin proteins. The remaining genes contain the instructions for making other parts of our bodies. If our Hemoglobin gene is normal, the hemoglobin protein works fine. But if the instructions in that gene are changed, or “mutated”, changes in the hemoglobin protein could result in disorder called sickle cell anemia.
What is Heredity? - Passing of traits from parents to child
Why do children look like their parents? Why do brothers and sisters resemble each other? This is because we "inherit" traits from our parents. Our genes encode the instructions that define our traits.
When parents conceive a child, they each contribute one complete set of chromosomes to the child. In this way, parents pass genes to the child. Every child receives half of its chromosomes from the mother and half from the father.
What is a trait?
A trait is a notable feature or quality in a person. Each of us has a different combination of traits that make us unique. Traits are passed from generation to generation. We inherit traits from our parents, and we pass
them on to our children.
There are:
  • Physical traits - hair color, eye color, height and blood type.
  • Behavioral traits - are characteristics of the way a person acts.
  • Predisposition to a medical condition – An increased risk of getting a certain type of disease or health condition; Some examples of such diseases are higher blood pressure, diabetes, sickle cell anemia, heart diseases, cancer and more.
  • Response to medications or drugs- people are prescribed drugs all the time, but prescriptions can be dangerous because people can have different responses to drugs.
Traits are the result of gene and environment interaction
Your observable traits, also known as your phenotypes, result from interactions between your genes and the environment. Differences in some phenotypes, like height, are determined mostly by genes. If you
have short parents and grandparents, you probably don't tower over your peers, though environmental factors like a healthy diet might give you a little lift. The non-genetic or “environmental” influences in our lives are just as important in shaping our traits. Sometimes these environmental factors can even change a trait! For example, if in genetics, a person may be born with an increased risk of heart disease, its environment, like eating healthy foods and exercising can reduce the risk.
What is a mutation or SNP? – 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 make everyone unique. Those differences can in turn influence a variety of traits such as appearance, disease susceptibility or response to drugs. While some SNPs lead to differences in health or physical appearance, most SNPs seem to lead to no observable differences between people at all. DNA is passed from parent to child, so you inherit your SNPs versions from your parents.
What are complex traits?
The specific degree of a complex trait is very difficult to predict from one generation to the next (e.g., the exact height of offspring). This is because the precise combination of genes contributing to the trait cannot be
predicted either (or, perhaps, even known). When geneticists look for evidence of genetic influence on a disease, such as heart disease, diabetes or high blood pressure, they look for families that have many affected over several generations. However, for complex traits there is not obvious pattern from one generation to the next.
What are dominant traits?
Unlike common complex traits, certain rare traits do show clear patterns of inheritance. In these traits, single genes strongly influence a trait in an 'either/or' manner. Dominant traits require only one copy of a gene to express the trait (e.g., ability to roll your tongue, Huntington disease).
copy of a gene to express the trait (e.g., ability to roll your tongue, Huntington disease).
What are recessive traits?
Recessive traits require two copies of a gene to express the trait (e.g., Beta-thalassemia, Hearing Impairments). A 'carrier' has only one copy of the gene for the recessive trait, so the carrier does not have the trait.