K12 Comparative Embryology

From Embryology

Introduction

All human and animal embryos go through very similar stages of early development. The major difference appears to be how long it takes to reach each of these same stages. We now also know that many of the underlying signals that regulate development are the same between these different species.

This page will introduce how we can compare the development of different animal embryos.


K12 Links: Start Here | Week 1 | Week 2 | Week 3 | Week 4 | Week 5 to 8 | Arms and Legs | Heart | Fetus | Brain Growth | Eyes and Ears | Animal Development Times | Humans and Animal Embryology | Comparative Embryology | Thalidomide


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This movie shows human embryo development between week 4 to 8 after fertilisation.

Human Carnegie Stages

Carnegie stages are named after the famous USA institute which began collecting and classifying embryos in the early 1900's. Human stages are based on the external and/or internal features of the embryo, and are not directly dependent on either age or size. The human embryonic period proper is divided into 23 Carnegie stages covering the first 8 weeks after fertilisation (post-ovulation). This period is most of the first trimester and the second and third trimester is called Fetal Development and is mainly about growth.

Human Carnegie stage 10-23.jpg
The Carnegie Embryos

Other features used in this classification include: ranges of age in days, number of segments (somites) present, and embryonic size (CRL, crown rump length). Similar types of measurements are also used to stage how animal embryos develop. You can therefore compare other animal embryos each other and to human development by using these staging criteria.


Week 4 to 5

This is what the human embryo looks like at the end of week 4 and the beginning of week 5 development (called Carnegie stage 13) about half way through embryonic development.

Stage13 crown rump length.jpg Stage13 surface bulges.jpg
Measuring embryo size (Crown Rump Length) Surface bulges (internal and external development)
Links: Carnegie Stages

Species Comparison of Carnegie Stages

This table shows a comparison between different animal embryos and human embryos using the same staging criteria. Note that researchers have also developed embryo staging criteria that is specific to a single species.

Carnegie stages species comparison.jpg

Links: Animal Development

Human and Mouse Embryo

The images below show a human and mouse embryo that appear externally close to the same stage of development.

Would you know which was which without the labels?

Human

Stage15 bf4.jpg Stage15 bf3.jpg Stage15 bf5.jpg Stage15 bf6.jpg

35 - 38 days, Week 5, 7 - 9 mm CRL (Carnegie stage 15)

Mouse

Mouse CT axes E11.5.jpg

11.5 days (Theiler Stage 19)

Animal Development

Frog lifecycle.jpg

Timeline rabbit.JPG


ANAT2341 group projects

Project 1 - Rabbit | Project 2 - Fly | Project 3 - Zebrafish | Group Project 4 - Mouse | Project 5 - Frog | Students Page | Animal Development

These are university undergraduate student designed pages describing the development of specific animal embryos.


Cite this page: Hill, M.A. (2024, March 28) Embryology K12 Comparative Embryology. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/K12_Comparative_Embryology

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G