Human genome

Inside your body, you have tiny plans.

These plans are called DNA. They tell your body how to work.

Most of these plans make food for your cells. This part is very small.

Most of the DNA does not make food. Some parts act like switches. They turn parts of the plan on or off.

Some parts are like old, broken copies. They do not work anymore. These are called pseudogenes.

Every person has a slightly different plan. This is why we are all unique!

Your body holds a complete set of instructions. Scientists call this the human genome.

It is made of DNA. This DNA is organized into parts called chromosomes. Humans have 22 pairs of matching chromosomes. We also have two sex chromosomes, known as X and Y.

Most of the genome is not used to make proteins. Proteins are the building blocks of your body. Only about 1% to 2% of your DNA codes for proteins. The rest is called non-coding DNA. Some of this DNA acts like a switch. These are regulatory sequences. They help control how genes work. Other parts are called pseudogenes. These are like old, broken copies of genes. They do not work anymore.

Some DNA can even move. These are called transposons, or "jumping genes." They can copy themselves and move to new spots. Scientists have studied the genome for a long time. They have mapped out billions of tiny pieces called base pairs. Every person has a genome that is a little bit different. This makes every human unique.

The human genome is the complete set of DNA instructions for a person. It includes 22 pairs of autosomes and two different sex chromosomes called X and Y.

You can also find a small amount of DNA inside tiny parts of cells called mitochondria. This whole collection is made of genes and many other types of DNA elements. Some parts act as scaffolding or help manage how DNA copies itself. Other parts are repetitive sequences that repeat the same patterns over and over. Scientists study these patterns to understand how life is built and how it works.

How the genome works involves many different moving parts. Most of the DNA is used to make proteins, which are vital for the body. These protein-coding genes make up about 40% of the genome. However, the actual coding sequences only account for about 1% to 2% of the total DNA. The rest is non-coding DNA, which includes many important roles. Some non-coding parts make RNA molecules that help build proteins. Other parts are regulatory sequences that act like switches to control gene expression.

History shows how much we have learned about these instructions. In 2000, scientists said they had sequenced 88% of the human genome. By 2020, at least 8% was still missing from the map. In 2021, researchers reported sequencing a complete female genome. The Y chromosome was later sequenced fully in January 2022. The current standard version is called GRCh38.p14, which was released in July 2023. This version helps scientists have a common map to study.

There are many specific facts about the size and variety of our DNA. The standard reference genome contains about 3.1 billion base pairs. Most human cells are diploid, meaning they hold about 6.2 billion base pairs. Even though we are similar, there are small differences between individuals. These differences are about 0.1% for single-nucleotide variants. In 2023, a draft called a pangenome was published using 47 different genomes. This helps scientists see the many ways human DNA can vary across the world.

Understanding the genome helps us see how we connect to the world. For example, humans have many pseudogenes, which are inactive copies of genes. In the human olfactory receptor gene family, over 60% are these non-functional copies. This helps explain why humans have a less sharp sense of smell than some other mammals. We also have "jumping genes" called transposons that can move around. Some of these are even old pieces of viral DNA that became part of us. These tiny details show how our history is written in our cells.

The human genome is the complete set of DNA sequences for an individual. It includes 22 pairs of autosomes and two distinct sex chromosomes, known as X and Y.

Most human cells are diploid, meaning they contain two sets of these chromosomes. This results in approximately 6.2 billion base pairs of DNA. A separate, small DNA molecule is also found within individual mitochondria. Scientists usually categorize these into the nuclear genome and the mitochondrial genome. Understanding the genome is vital for studying how life is built and how it functions.

The genome functions through a complex system of coding and non-coding elements. Protein-coding genes are the most widely studied component of the genome. These sequences lead to the production of all human proteins. The human reference genome contains between 19,000 and 20,000 of these genes. Interestingly, these genes contain an average of 10 introns, which are non-coding sections within a gene. The average size of a protein-coding gene is about 62 kb. While these genes take up about 40% of the genome, the actual coding DNA is only 1% to 2%. The remaining 98% to 99% is classified as non-coding DNA.

Non-coding DNA is far from useless; it performs many essential roles. Noncoding RNA molecules are critical for protein synthesis and RNA processing. These include types like tRNAs, ribosomal RNAs, microRNAs, snRNAs, and long non-coding RNAs (lncRNAs). Many of these molecules are vital for gene regulation and expression. Furthermore, noncoding RNA contributes to epigenetics and the translational machinery. Another major component is regulatory DNA. These sequences act as control switches for gene expression. Some scientists estimate regulatory sequences make up 8% of the genome, while others suggest they may account for 20% or more.

Another fascinating part of the genome involves repetitive DNA sequences. These sequences make up approximately 50% of the total human genome. About 8% consists of tandem DNA arrays, which are adjacent copies of a sequence. These include microsatellites, which are repeats of fewer than ten nucleotides. Trinucleotide repeats are particularly important because they can occur in coding regions. For example, an expansion of the (CAG)n repeat in the Huntingtin gene causes Huntington's disease. There are also longer arrays called minisatellites. These highly variable sequences are often used in forensic DNA analysis and genealogical testing.

Transposable elements, often called "jumping genes," also shape our genetic makeup. These are DNA sequences that can replicate and insert copies of themselves into new locations. The most abundant lineage is Alu, with about 50,000 active copies in the genome. Another lineage, LINE-1, has about 100 active copies per genome. Together with non-functional relics, these elements account for over half of all human DNA. Some of these are endogenous retroviruses, which are viral DNA sequences permanently integrated into our genome. At least three of these have proven functions, such as HERV-K. Others, like HERV-W and HERV-FRD, help in placenta formation during pregnancy.

History shows the incredible progress made in sequencing these instructions. In 2000, the Human Genome Project reported sequencing 88% of the genome. By 2020, at least 8% was still missing. In 2021, researchers successfully sequenced a complete female genome. The Y chromosome, which consists of 62,460,029 base pairs, was fully sequenced in January 2022. The current standard reference is GRCh38.p14, released in July 2023. This reference contains approximately 3.1 billion base pairs. In 2023, a draft human pangenome reference was published using 47 genomes from diverse ethnicities to better capture human biodiversity.

Comparing humans to other species reveals how the genome evolves. Humans have many pseudogenes, which are inactive, nonfunctional copies of protein-coding genes. There are approximately 13,000 pseudogenes in the human genome. For example, over 60% of the olfactory receptor gene family in humans consists of pseudogenes. This is much higher than the 20% found in mice. This specific genetic trait helps explain why humans have a less acute sense of smell than many other mammals. While humans and chimpanzees are closely related, they differ by about 1.1% in fixed single-nucleotide variants. These genomic details show how evolution leaves a permanent map within our cells.