Genetic Overview
What are Chromosomes?
What are Genes?
What is DNA?
What are Biological Samples?
What is a Genetic Analysis?
Genetic Analogy
What are Chromosomes?
Our bodies are composed of millions of cells. Within the center of each cell are rod-like structures known as chromosomes. Typically, there are 46 chromosomes in each cell. They are grouped into 23 pairs, one member of each pair comes from our mother and the other from our father at the time of conception. The first 22 pairs of chromosomes are the same in both men and women and are numbered 1 through 22. The last two determine our sex and are called X and Y. Women have two X chromosomes, and men have one X chromosome and one Y chromosome.
What are Genes?
Our chromosomes carry our genes, the basic units of heredity. Our genes are stretches of DNA that give our bodies the instructions to grow and develop properly. There are approximately 20,000 genes that influence our growth and development. Each gene occupies a specific location on a chromosome. With the exception of the X and Y chromosomes, there are two copies of each chromosome and therefore two copies of each gene. When a mistake or an alteration occurs in one or more genes, the body may not develop properly and this can lead to a genetic disease.
What is DNA?
Our genes are composed of DNA which is made up of four chemical bases, represented by letters: adenine (A), guanine (G), cytosine (C), and thymine (T). These bases are strung together in pairs (base pairs) in specific combinations and lengths to spell our genes. When the base pair sequence is altered, our DNA code is altered, and this can lead to a genetic disease.
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What are Biological Samples?
The complete set of our genes are present in nearly every cell of our body. A blood sample is the most common type of biological sample that is used for a genetic analysis, but saliva samples, amniotic fluid, skin samples, and other tissue samples can also be used for a genetic analysis. Sometimes it is important to study multiple tissue types from one individual as the genetic information in one tissue type may be different from the genetic information in another tissue type.
What is a Genetic Analysis?
A chromosome analysis (karyotype) is the most basic genetic analysis. A chromosome analysis is able to detect missing or extra chromosomes or other large chromosome abnormalities but cannot detect small chromosome abnormalities or single gene abnormalities. A DNA microarray is able to detect the small deletions or duplications of DNA that cannot be detected by a chromosome analysis. The genetic analysis performed as part of our research study is Whole Exome Sequencing (WES). This test analyzes all 20,000 genes found on our chromosomes via gene sequencing. The study is also utilizing newer genetic testing called Whole Genome Sequencing (WGS). The 20,000 genes that create proteins in our bodies account for approximately 2% of our DNA. Most genetic diseases are caused by mutations in this 2% of DNA, however there may be additional mutations in the remaining 98% that can affect a person’s health. Whole Genome Sequencing analyzes the entirety of an individual’s DNA in an effort to identify these additional mutations.
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Genetic Analogy
Sometimes it is helpful to use an analogy to better understand information about our genes and how we use genetic analyses to examine our genes.
46, XY; Male karyotype
Our chromosomes are like a set of 46 encyclopedia books. A chromosome analysis or karytype is able to determine if there are any missing or extra books (chromosomes).
Computerized results of a DNA Microarray
Our genes are like the sentences on each page of the set of encyclopedia books (chromosomes). Each page of each book contains a unique set of sentences (genes). Each page contains the sentences for approximately 10 to 30 genes. A DNA microarray analysis is able to open up each of the 46 encyclopedia books to determine if there are any missing or extra pages. Click here to learn more about DNA microarray analysis.
Computerized results of genetic sequencing
Our DNA are like the letters that make up each sentence (gene) on each page of the books (chromosomes). Each sentence is made up of a very specific sequence of letters (DNA). Genetic sequencing is able read a specific sentence to determine if there are any spelling mistakes (genetic mutations) in the sentence (gene). Click here to learn more about genetic sequencing.
