When the human genome is examined, the chromosomes appear to have undergone only minimal rearrangement in the 100 million years since the last common ancestor of eutherian mammals. However, when individual humans are examined or when the human genome is compared with that of chimpanzees, a large number of small indels and SNPs can be detected. How are these observations reconciled?

Key Concepts

Chromosomal Rearrangement

Chromosomal rearrangement refers to alterations in the structure or number of chromosomes, which can include duplications, deletions, inversions, and translocations. In the context of eutherian mammals, the observation of minimal rearrangement over 100 million years suggests that large-scale structural changes are relatively rare, allowing for the conservation of chromosome organization across species.

Indels and SNPs

Indels (insertions and deletions) and SNPs (single nucleotide polymorphisms) are types of genetic variations that occur within a genome. Indels involve the addition or loss of small DNA segments, while SNPs are variations at a single nucleotide position. These variations contribute to genetic diversity and can have significant implications for traits and disease susceptibility, despite the overall stability of chromosome structure.

Evolutionary Genetics

Evolutionary genetics studies the genetic basis of evolution, focusing on how genetic variation leads to evolutionary change. The apparent contradiction between minimal chromosomal rearrangement and the presence of numerous indels and SNPs can be reconciled by understanding that while large structural changes are infrequent, small-scale mutations accumulate over time, driving adaptation and speciation without altering chromosome architecture significantly.