K12 Comparative 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.
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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.
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.
Exercise 1 - Embryo Size | |
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How big is the human embryo? Download and Print the Worksheet
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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.
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.
- Links: Animal Development
Human and Mouse Embryo
The images below show a human and mouse embryo that appear externally at the same stage of development.
- Would you know which was which without the labels?
Human
Week 5, 35 - 38 days, 7 - 9 mm CRL
Mouse
11.5 days
Animal Development
Teacher Note | |
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Currently only a series of related images.
I am writing explanatory notes and associated exercises for this section when I have some spare time. You can also let your students look at the animal pages designed by my students back in 2009. Each page includes images of the embryos and a timeline of development for each animal embryo. --Mark Hill 11:54, 22 June 2012 (EST) |
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, June 15) Embryology K12 Comparative Embryology. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/K12_Comparative_Embryology
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G