TAG: GS 3: ECOLOGY AND ENVIRONMENT
THE CONTEXT: The absence of a tail is a distinctive feature of apes, setting them apart from monkeys. While all mammals develop a tail at some point during embryonic development, apes lose theirs in utero, leaving behind vestigial vertebrae known as the coccyx or tailbone. The evolutionary origin of this phenomenon remained a mystery until recent breakthrough research shed light on a pivotal DNA change occurring 25 million years ago.
EXPLANATION:
Unraveling the Genetic Basis of Tail Loss:
- Researchers identified a crucial DNA insertion event between segments of the TBXT gene (a gene already known as one of many involved in tail formation in monkeys) that led to the loss of tails in apes.
- This insertion prevented the production of a functional protein necessary for tail formation.
- The TBXT gene, known for its role in tail formation in monkeys, became a focal point of investigation.
The Role of ‘Junk’ DNA:
- Previously dismissed as non-functional, ‘junk’ DNA has emerged as a critical regulator of gene expression and genome stability.
- Within this non-coding region, primate-specific transposable elements, such as the Alu element, play a significant role.
- Despite its small size, the Alu element’s ability to insert and replicate within the genome has far-reaching consequences, as demonstrated by its involvement in the tail loss of apes.
The Alu Accident:
- Approximately 25 million years ago, an Alu insertion event occurred in the zygote of an ancient ape ancestor, altering the genetic code responsible for tail development.
- This chance event, with a probability of one in a million, became permanently imprinted in the DNA of all subsequent ape species, marking the divergence of apes from their tailed ancestors.
Functional Implications of the TBXT Mutation:
- The Alu insertion disrupted the stitching together of gene segments, resulting in a defective TBXT protein incapable of promoting tail formation.
- Experimental evidence using mouse embryos engineered to express the mutated TBXT confirmed its role in tail loss, providing crucial insights into the evolutionary consequences of this genetic alteration.
Beyond Tail Loss:
- The impact of the TBXT mutation extended beyond tail loss, leading to neural tube defects and necessitating compensatory genomic changes.
- These adaptations underscore the intricate interplay between genetic mutations and evolutionary pressures, highlighting nature’s ability to capitalize on rare events to drive species divergence and adaptation.
Implications for Human Evolution:
- The loss of the tail has been linked to the emergence of bipedalism in human ancestors, though the exact evolutionary advantage remains speculative.
- Nonetheless, the evolutionary significance of the TBXT mutation lies in its role as a catalyst for the divergence of apes, including humans, and their subsequent dominance on Earth.
FOR FURTHER INFORMATION, KINDLY REFER TO THE 8TH APRIL 2024 DNA TOPIC.
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