Gene Regulation: Hox Genes | A-level Biology | OCR, AQA, Edexcel

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The key points covered in this video include:
1. Homeotic Genes
2. Hox Genes
3. Hox Genes and Animal Development
Homeotic Genes
One of the roles of DNA is to contain the instructions necessary for building the bodies of organisms. DNA contains genes that regulate morphogenesis, which is the process that causes an organism to form its shape. These genes are called homeotic genes. A subset of homeotic genes are called homeobox genes which contain a 180 base pair length of DNA called a homeobox. The homeobox sequence is highly conserved in plants, animals and fungi. Conserved genes are genes that have remained unchanged throughout the evolution of different descendent species. The homeobox sequence codes for a specific sequence of 60 amino acids within the synthesised protein called homeodomain. The homeodomain sequence folds into a specific shape consisting of three a-helices. The second and third helix create a helix-turn helix which consists of two a-helices connected by a short loop of amino acids. The helix-turn helix shape allows the protein to bind to DNA and regulate the transcription of nearby genes. The proteins that contain a homeodomain are therefore transcription factors.
Hox Genes
A subset of homeobox genes are called genes. Hox genes are homeobox genes that are only found in animals. Hox genes are involved in the correct positioning of body parts in an organism. Hox genes are found in all bilaterian animals suggesting that Hox genes must have existed in the common ancestor of all bilaterians. Several Hox genes are found next to each other on a chromosome - they are arranged in clusters. In some animal lineages, including vertebrates, Hox genes have been duplicated, resulting in multiple Hox clusters. When a Hox gene is mutated, body parts end up developing in the wrong place on the body - these are called homeotic mutations.
Hox Genes and Animal Development
Hox genes are expressed in early embryonic development along the anterior-posterior (head-tail) axis of the organism. Interestingly, the order of the genes on the chromosomes matches the expression patterns along the embryo, showing spatial linearity. As well as spatial linearity, the expression of the genes also occurs in temporal order, starting with expression of the anterior Hox genes. This phenomenon is known as colinearity and scientists do not yet understand the importance of this for Hox genes. When each Hox gene is expressed, it encodes a specific Hox protein that acts as transcription factor. This transcription factor binds to specific regions of DNA and switches on a specific set of genes in each segment. These activated genes help promote the correct development of each body segment by regulating mitosis, apoptosis and cell differentiation.
Summary
Homeotic genes regulate morphogenesis - the process in which an organism forms its shape during development
A subset of homeotic genes are homeobox genes
Homeobox genes contain a 180 base pair homeobox which is a conserved sequence of DNA found in plants, fungi and animals
A subset of homeobox genes are Hox genes which are only found in animals
Hox genes regulate the correct positioning of body parts in an organism
Hox genes are expressed along the anterior-posterior axis in spatial and temporal order
Each Hox gene encodes a different Hox transcription factor which activates a specific set of genes in each segment
These activated genes promote the correct development of each body segment

[@Dredlock68]

Not doing A-Level Biology, just a 55 year old here out of interest. You explain it so super clear that even someone like myself was able to understand. Thank you.

[@NelleJohn01]

This is the first clear explanation of the differences in homeotic, homeobox and HOX that I've come across. Thank you so much

[@amynugent2075]

@Reese Flynn shut up

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I stupidly lost my password. I appreciate any help you can give me.

[@Chloe-AmeliaChapmanYear13]

Honestly this is the first time I've grasped this in such an easy way, as an a level student sitting her exam tomorrow thank you!!

[@harrystarkey5945]

Thanks! this was so helpful compared to textbooks and lectures

[@thirsty1629]

My university lecturer spent an hour discussing hox genes and couldn't teach anywhere as well as snaprevise. Happy holidays for anyone watching ⛄🎄

[@bilbo90161]

This was a lifesaver, thank you so much!!

[@JonathanSagdahlYT]

Very thorough and clear explanation. Great video!

[@bowandarrow8100]

OMG! This is explained so well! Also thank you for speaking so clearly and slowly, even someone like me how is not a native speaker can understand you. Thank you

[@Jojo-kl6tx]

A-level biology - oof, I'm in my master's😅 what a great video, straightforward and simple explanations, and everything was so clearly structured and set into context - I love it!

[@theoldhip]

I've had several courses in molecular bio - This is one of the clearest beginning explanations for HOX that I've experienced. Thank-you.

[@brentweissert6524]

thank you so much for this. i've nearly driven myself batty trying to sort all this out. At last it is clear and i can sleep tonight! keep videos like this coming.

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Thanks a lot I‘m not even an English Native Speaker, currently doing A Levels in Germany, but in my languages there are no videos to this topic, thanks a lot, even though I couldnt understand everything, i still now atleast got a foundation in this topic

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Thanks again

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Finally i got a clear explanation. Thank you so much sir

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Great instruction.

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I love these explanations. Could you think in the future to add subtitles in Spanish? Thank you for your work

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It was so easy-to-grasp! Thanks a ton!

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very clear explanation! thank you!

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Amazing and clear explanation thank you

[@tejass527]

Now I understood this sir, thanks for the wornderdfull lecture

[@angelamarie709]

Thank you! It makes much more sense now.

[@Bahrzy2002]

I am highly interested in this subject but I haven't seen a video that explains how the hox genes get regulated themselves. I am curious about how your body 'knows' when to turn on a different hox gene to form the next bodypart. I get that they are in order and code for different bodyparts, but how do the cells at the end of my arm suddenly get the information to start developing a hand? I really hope you can tell me this.

[@casita4705]

I think this ocurrs because in the cell differentiation while you arm is building up, the arm cells yield proteins as a product of gene expression to form the arm, but in turn, those proteins also regulate the expression of the genes that will form the hand

[@biancamn1226]

I think it's the morphogens that regulate that

[@akanshakamble2946]

Very well explained!! My doubts are clear now.

[@IlPiccoloNerd]

Great, clear and concise information. Thanks

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Clear and Well Explained 👍

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so so helpful thank you!

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Great video!!!!!

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Very nice explained, thank you!

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Thank you so much! Please keep the videos coming.

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Good clarity👌

[@chiaracremonesi5317]

Thanks for the explanation, the best I found :)

[@Hana-fj4dj]

thank you so much for this explanation!

[@yanyisun5704]

Sooooo clear！ Thank you

[@threethrushes]

Good summary with some acceptable approximations (e.g. that Homo sapiens have perfect bilateral symmetry - we do not).

[@aswathy_babu]

Great .... Well explained

[@abdullahhajasad9332]

Thank you for this Great video ,I found it crystal clear
But how homeobox genes are turned On and Off in different stages of development of the organism?

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Well done.Keep it up!

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Thank You!

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You're welcome!

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thanks a lot!

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“I used the gene to block the gene”

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Axel Mountains

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wait you guys learn hox genes at a levels?!?! baffled as a biology student at university and a former ib student....

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Huels Courts

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one person has a thumb at the wrong place

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[@Anna-qz8sj]

thanks for this very clear explanation!