Human genetic variation facts for kids
Human genetic variation means the tiny differences in DNA that make each person unique. Even though we all look like humans, our bodies are built using slightly different instructions. These differences happen both between groups of people and within the same group.
Think of it like this: everyone has a recipe book (their DNA). While the main recipes are the same for all humans, there are small changes in the ingredients or steps. These small changes are called alleles. When there are many different versions of a gene in a population, it's called polymorphism.
No two people are exactly the same genetically. Even identical twins, who start from the same single cell, can have tiny differences. This is because small changes (called mutations) can happen as they grow. These unique differences are why genetic fingerprinting works to identify people.
Our entire set of DNA, called the human genome, is huge! It has about 3.2 billion base pairs, which are like the letters in our DNA code. This code is spread across 46 chromosomes. We also have a small amount of DNA in our cells' powerhouses, called mitochondria. Scientists have found hundreds of millions of these small differences between people.
Compared to some other animals, humans are quite similar genetically. For example, rhesus macaque monkeys have much more DNA diversity than humans. Most of the genetic differences among humans are found within populations, not just between them. This means that people from the same country or region can be very different genetically from each other.
Because of this, scientists say there's no real scientific basis for dividing humans into "races" or "subspecies." We are all one species. However, some genetic differences are more common in certain parts of the world. These include things like skin color, body size, how well people digest milk (lactose) or starch, and how they adapt to high altitudes.
The greatest amount of genetic diversity is found in Africa. As you move further away from Africa, the diversity gradually decreases. This supports the idea that modern humans first came from Africa and then spread across the world.
Studying human genetic variation is important for understanding our past and for medicine. It helps scientists figure out how people moved around the world long ago. In medicine, it helps us understand why some diseases are more common in certain groups. For example, the gene for sickle-cell anemia is more often found in people whose families came from parts of Africa, Southern Europe, Arabia, and India. This is because this gene can offer some protection against malaria, a disease common in those areas.
Scientists have also found that each person has about 60 new genetic changes (mutations) that their parents didn't have.
How Genetic Differences Happen
Differences between people happen in several ways. When parents pass on their genes to their children, the genes are mixed in new ways. This happens through processes like independent assortment and the exchange of genes (called crossing over and recombination) during meiosis. Also, new mutations can appear randomly in our DNA.
There are also reasons why genetic differences exist between different groups of people:
- Natural Selection: Sometimes, a specific genetic change (an allele) can give people an advantage in a certain environment. For example, if an allele helps people survive a disease, it might become more common in that area.
- Genetic Drift: This is when random changes happen in the genes of a population. It's like a game of chance. If a small group of people moves to a new area, the genes they carry might be different from the larger group they left behind. Over time, these random changes can become more common in the new population.
- Founder Effect: This is a type of genetic drift. When a small group of people leaves a larger population to start a new one, they only carry a small part of the original group's genetic diversity. The new population will then have different genes that are more common, and it will be less genetically diverse than the original group.
In humans, genetic drift is the main reason for many of the neutral (neither good nor bad) genetic differences between populations. The "founder effect" and small population sizes in the past made genetic drift more likely. While most mutations are neutral, a small number of genes have changed recently due to natural selection, often because of specific environmental pressures in certain regions.
See also
In Spanish: Variación genética humana para niños
- Archaeogenetics
- Chimera (genetics)
- Genealogical DNA test
- Human evolutionary genetics
- Isolation by distance
- Multiregional hypothesis
- Neurodiversity
- Race and genetics
- Recent single origin hypothesis
- Y-chromosome haplogroups in populations of the world
