Why Siblings Aren’t Identical: Understanding Genetic Variation — Reading Comprehension

If you've ever noticed that you and your siblings don’t look exactly alike, it’s because of genetic variation. Genetic variation means that each individual has a unique set of genetic traits, even when they come from the same parents. This happens because of the way sexual reproduction works.

In sexual reproduction, each parent contributes half of the offspring’s DNA. These pieces come together to form a new combination of genes. Since there are many possible ways that genes can combine, no two siblings (except identical twins) get exactly the same mix. This is why one child might have curly hair while another has straight hair, or why siblings can have different eye colors or heights.

Genetic variation is important for survival. It gives species a better chance of adapting to changes in their environment. For example, if a disease affects a group of animals, some individuals may carry genetic traits that help them resist it. These animals are more likely to survive and pass on their helpful traits to the next generation.

In contrast, asexual reproduction does not create variation. Offspring are clones—exact genetic copies of the parent. This is useful when conditions are stable, but it can be risky if the environment changes. With no variation, the entire population might be vulnerable to the same threat.

Understanding genetic variation helps explain why no two people (except clones or identical twins) are exactly the same, even within the same family.

Fun Fact: Humans share 99.9% of their DNA with each other—it's the tiny 0.1% difference that makes each person unique!

What is genetic variation?

Why are siblings not exactly alike?

What percent of DNA do all humans share?

What causes genetic variation in sexual reproduction?

Why is genetic variation important to a species?

What is a risk of asexual reproduction?

What is the main idea of the passage?

If a disease spreads in a species, how might variation help?