IB Biology Topic A3.1.8: Unity and Diversity of Genomes Within Species Notes

The Genome Allows for Genetic Diversity within Species

1. The genome is the instruction manual for building and maintaining an organism, written in the four DNA bases A, T, C, and G.

Unity Within a Species

1. All members of a species share the same set of genes arranged in the same order on their chromosomes.
2. This shared structure ensures that organisms can reproduce successfully, allowing homologous chromosomes to pair, align and cross over correctly during meiosis.

Small Genetic Variations Called SNPs Differentiate Individuals Within a Species

While genomes are largely uniform within a species, small variations exist, creating individual uniqueness.

Single-Nucleotide Polymorphisms (SNPs)

1. The most common source of variation is the single-nucleotide polymorphism (SNP).
2. SNPs occur roughly once every 1,000 base pairs in humans, so a human genome contains several million SNPs.

Why Are SNPs Important?

1. Trait Variation: SNPs contribute to differences in height, fur color, or disease resistance.
2. Evolutionary Insights: They act as markers to trace inheritance patterns and evolutionary relationships.
3. Individual Uniqueness: SNPs drive the subtle variations that differentiate individuals within a population.

Unity and Diversity Across Species

1. Within species: Humans share approximately 99.9% of their DNA with each other. This explains why all humans belong to the same species and can reproduce together.
2. SNPs and other variations account for the 0.1% difference between individual humans, explaining why people look and behave differently despite being the same species.