A chromosome includes diploid sister chromatids (they are in pairs) around a haploid centromere (a singular one) Chromosomes are used in plenty of things like replacing dead skin, creating new body cells, and healing wounds.
Variation is any difference in organisms of the same species, whereas gradualism is a microevolutionary theory.
<h3>What is a scientific theory?</h3>
A scientific theory is a given explanation on a phenomenon from the real world (e.g., the evolution theory).
The fossil record is a piece of evidence for the evolution theory (which is mainly based on natural selection).
In conclusion, variation is any difference in organisms of the same species, whereas gradualism is a microevolutionary theory.
Learn more about natural selection here:
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B, overfishing in coral reef ecosystems