January 28, 2025
A Level Biology Revision (Year 13)

A Level Biology Revision (Year 13) “Homeobox Genes and Body Plans”

Author: Freesciencelessons via YouTube
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A Level Biology Revision (Year 13)

In this video, we look at homeobox genes and body plans. First we explore what is meant by a homeobox gene and why homeobox genes are transcription factors. We then look at Pax6 and its role in eye development. We explore diploblastic and triploblastic organisms and segmentation. We then look at Hox genes and how they direct the development of somites in the embryo. We explore the roles of mitosis and apoptosis in the development of body plans. Finally, we look at how development can be influenced by external factors including drugs such as thalidomide.

Image credits:

Zygote
https://commons.wikimedia.org/wiki/File:Zygote1.jpg
Nina Sesina, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Human embryo 8 cells
https://commons.wikimedia.org/wiki/File:Embryo,_8_cells.jpg
ekem, Public domain, via Wikimedia Commons

3 month old foetus
https://commons.wikimedia.org/wiki/File:4dsonogram.jpg
Madcapslaugh, Public domain, via Wikimedia Commons

Goose
https://commons.wikimedia.org/wiki/File:Graugans_Anser_Anser.jpg
H005, denoised by Pro2, Public domain, via Wikimedia Commons

Large eyed mini wolf spider
https://commons.wikimedia.org/wiki/File:Large-eyed_mini_wolf_spider_(Minicosa_neptuna).jpg
RudiSteenkamp, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Daffodil
https://commons.wikimedia.org/wiki/File:Narzisse.jpg
Martin Hirtreiter, CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons

Hox genes of fruit fly
https://commons.wikimedia.org/wiki/File:Hoxgenesoffruitfly.svg
PhiLiP, Public domain, via Wikimedia Commons

Fruit fly
https://commons.wikimedia.org/wiki/File:Drosophila_melanogaster_-_side_(aka).jpg
André Karwath aka Aka, CC BY-SA 2.5 https://creativecommons.org/licenses/by-sa/2.5, via Wikimedia Commons

Pax6 mutations
https://commons.wikimedia.org/wiki/File:PAX6_Phenotypes_Washington_etal_PLoSBiol_e1000247.png
Washington NL, Haendel MA, Mungall CJ, Ashburner M, Westerfield M, Lewis SE., CC BY 2.5 https://creativecommons.org/licenses/by/2.5, via Wikimedia Commons

Antennapedia mutant
https://commons.wikimedia.org/wiki/File:Mutation_Antennapedia.jpg
toony, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Homeobox genes big picture (modified by S. Donnelly)
https://commons.wikimedia.org/wiki/File:Genes_hox.jpeg
Stefanie D. Hueber, Georg F. Weiller, Michael A. Djordjevic, Tancred Frickey, CC BY 4.0 https://creativecommons.org/licenses/by/4.0, via Wikimedia Commons

1NK2-NK2 homeodomain
https://commons.wikimedia.org/wiki/File:1NK2-NK2_homeodomain_DNA_complex.png
Takuma-sa, CC0, via Wikimedia Commons

Jellyfish
https://commons.wikimedia.org/wiki/File:Chrysaora_jelly.jpg
This image is in the public domain.

Somites in mouse foetus
https://commons.wikimedia.org/wiki/File:Scanning_electron_micrograph_of_an_11.5_day_old_mouse_foetus_showing_the_limb_buds,_somites_and_branchial_arches.jpg
Paul Martin, CC0, via Wikimedia Commons

Gastrulation (modified by S. Donnelly)
https://commons.wikimedia.org/wiki/File:Early_gastrulation_in_amphibian_embryos.png
Kumar, V.; Park, S.; Lee, U.; Kim, J., CC BY 4.0 https://creativecommons.org/licenses/by/4.0, via Wikimedia Commons

Jellyfish 3
https://commons.wikimedia.org/wiki/File:Aurelia_aurita_2.jpg
© Hans Hillewaert

Jellyfish 4
https://commons.wikimedia.org/wiki/File:Aurelia_aurita_(auge24eu).jpg

Andreas Augstein, CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons

Butterfly
https://commons.wikimedia.org/wiki/File:Inachis_io_Lill-Jansskogen.JPG
Korall, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Somites in chick
https://commons.wikimedia.org/wiki/File:Aves_Neural_tube_and_somites_in_chick_embryo.jpg
Prof. R. Bellairs, CC BY 4.0 https://creativecommons.org/licenses/by/4.0, via Wikimedia Commons

Centipede
https://commons.wikimedia.org/wiki/File:Chilopoda-_Geophilomorpha_(3310072328).jpg
Mick Talbot from Lincoln (U.K.), England, CC BY 2.0 https://creativecommons.org/licenses/by/2.0, via Wikimedia Commons

Earthworm
https://commons.wikimedia.org/wiki/File:Earthworm_02.jpg
Rob Hille, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Snake skeleton
https://commons.wikimedia.org/wiki/File:Bitis_gabonica_complete_skeleton.jpg
Stefan3345, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Mouse embryo hand
https://commons.wikimedia.org/wiki/File:Handentwicklung_Maus_vier_Phasen.jpg
Ventus55, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Thalidomide
https://commons.wikimedia.org/wiki/File:Thalidomide_structure.svg
Aethyta, Public domain, via Wikimedia Commons

AI Avatar
https://commons.wikimedia.org/wiki/File:AI_Avatar.jpg
PedroXBC, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

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