Summary
Heterochrony and microRNA pathways such as let-7 control when developmental events occur.
In depth
Heterochronic genes in C. elegans (lin-4, let-7, lin-28) control larval stage transitions. Segmentation clock in somitogenesis. Neoteny and progenesis create evolutionary changes.
Timing mechanisms include clocks and sequential gene expression. Heterochronic changes (earlier or later development) cause evolutionary shifts in form.
Key idea: when something happens in development can matter as much as what happens.
Development relies on events happening in the right order and at the right time. Heterochrony, an evolutionary shift in timing, explains differences such as neoteny in axolotls (retaining larval features as adults) and the prolonged juvenile period of humans.
In C. elegans, genes of the heterochronic pathway (lin-4, let-7, lin-14, lin-28) control larval stages. lin-4 was the first microRNA discovered (Ambros and Ruvkun, Nobel Prize 2024) and let-7 is conserved in humans, where it promotes differentiation and acts as a tumour suppressor. The segmentation clock in somites is another timer.
Example: mutations that delay timing cause cells to repeat earlier fates.
Key idea: small changes in timing can alter body form.
Frequently asked questions
What is Developmental Timing?
Heterochrony and microRNA pathways such as let-7 control when developmental events occur.
Which area of biology covers Developmental Timing, and how advanced is it?
Developmental Timing is one of the 54 topics in Developmental Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Model Organisms in Development, Evo-Devo of Body Plans, Ageing and Development.
Can you give an example of Developmental Timing?
Humans retain juvenile features such as a flat face (neoteny).
What should I learn before Developmental Timing?
Work through the Beginner topics in Developmental Biology first, such as Fertilisation, Zygote, Embryo, then return to Developmental Timing. Advanced topics assume the Intermediate vocabulary.
What topics are related to Developmental Timing?
The closest topics to Developmental Timing are Model Organisms in Development, Evo-Devo of Body Plans, Ageing and Development, Hox Genes. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Developmental Timing?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Developmental Timing. To practise the whole of Developmental Biology, use the Developmental Biology quiz.
How is Developmental Timing different from Model Organisms in Development?
Developmental Timing: Heterochrony and microRNA pathways such as let-7 control when developmental events occur. Model Organisms in Development: Fruit flies, zebrafish, mice and C. elegans reveal conserved developmental mechanisms. Read both side by side and note what each one explains.
How should I study Developmental Timing step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Model Organisms in Development and explain the difference aloud. Finally, take the Developmental Biology quiz and come back to this page for any question you miss.