Genetics 101
Genetics 101: The Basics DNA, Genes, and Chromosomes
Think of DNA like a language that tells the body how to grow and function.
- DNA is like a book written with a four‑letter alphabet.
- Genes are like sentences in that book. Each gene carries instructions for a specific job, such as how brain cells communicate or how the body uses energy.
Genes are packaged inside structures called chromosomes.
Most people have 23 pairs of chromosomes, for a total of 46. One chromosome in each pair comes from each biological parent. Chromosomes are numbered from 1 to 22, plus one pair of sex chromosomes.
Our focus is on chromosome 16, and specifically a region called 16p11.2.
What Does “16p11.2” Mean?
Chromosomes are divided into regions, much like addresses.
- 16 refers to chromosome 16
- p means the short arm of the chromosome
- 11.2 describes the exact band location
This region contains around 20–30 genes that play important roles in brain development, learning, behavior, and metabolism.
What Is a Genetic Variance?
A genetic variance means there is a change in how DNA is arranged. This can include missing or extra pieces of DNA. These changes are sometimes called mutations, but genetic variance is a broader and more accurate term.
One common type of genetic variance is called a copy number variation, or CNV. CNVs describe sections of DNA that are missing, called deletions, or present in extra copies, called duplications.
These changes usually happen by chance as DNA is copied when cells grow and divide. Genes also do not work on their own. How they affect a person is shaped by health, environment, education, and access to therapies.
Why Other Genes Matter Too
Even when the same part of chromosome 16 is involved, people can be affected very differently. This is because everyone has many small differences in other genes across their DNA. These other genes can change how a 16p11.2 genetic variation shows up, making symptoms milder or more noticeable. Genes also often have more than one role in the body, so a change in one area can affect many systems, not just a single trait.
Deletion and Duplication
In a deletion, a section of DNA is missing, which can reduce important genetic instructions and affect how the body works. In a duplication, there is an extra copy of a DNA section, which can increase or disrupt how certain genes are used. In rare cases, there can be more than one extra copy, called a triplication, meaning the body has three copies instead of the usual two.
Deletions, duplications, and triplications can all affect development, but their effects vary widely from person to person.
Families who want clear, easy‑to‑understand explanations can explore trusted guides from Simons Searchlight and Unique – The Rare Chromosome Disorder Support Group, both of which use plain language and helpful visuals:
Why and When Do 16p11.2 Variances Occur?
Many 16p11.2 genetic variances happen by chance. Some are called de novo, which means the change is new and not found in either biological parent. These changes can occur when egg or sperm cells are forming, or very early after conception, as DNA is copied and organized. De novo changes are common in 16p11.2 conditions, especially in many deletion cases.
Not all 16p11.2 variances are new. Some are inherited from a parent. In general, many duplication cases are inherited, while many deletion cases are de novo, though this can be different for each family. These genetic changes are a natural part of how human DNA varies over time and are not caused by anything a parent did before or during pregnancy.
Understanding a Genetic Test Result
Many families receive results from a test called a chromosomal microarray.
A report might include:
- Chromosome number (such as 16)
- Region name (such as p11.2)
- Coordinates (numbers showing start and end points)
- Type of change (deletion or duplication)
- Size of the change (often in kilobases or megabases)
- Inheritance (de novo or inherited)
Each piece helps describe which genes are involved.