Dissertation

Comparative genomics of the balanced lethal system in Triturus newts

All crested and marbled newts (the genus Triturus) suffer from an unusual genetic abnormality, called a balanced lethal system, that kills exactly half of their offspring. How can a trait so disadvantageous have survived millions of years of natural selection?

Author: J.M. France
Date: 03 April 2025
Links: Thesis in Leiden Repository

It had previously been discovered that Triturus’s chromosome 1 occurs in two distinct versions, and both are necessary for survival. However, nothing was known about what made these two versions of the chromosome special, or how they might have evolved. We test a hypothesis that proposes that chromosome 1 evolved from a Y-chromosome. Surprisingly we find that Triturus do have different Y-chromosomes from their closest relatives, but while this is interesting evidence of rapid sex chromosome evolution, it does not fit with the evolution of chromosome 1. We build a map of the Triturus genome and compare it to other newts. We discover that the entire balanced lethal system has evolved in a single mutation, which deleted a gigantic chunk of DNA from each of the two versions of chromosome 1 while duplicating the same section on the opposite version. This explains why having both is necessary to survive (because otherwise an embryo would be missing hundreds of important genes).