A2 Epistasis 1: dominant epistasis

A2 OCR Biology revision: dominant epistasis

[@Uncle_Andrew086]

6 years on and you are still saving us. Thank you 🙏

[@xTj321x]

You deserve an award...seriously

[@gratitude2346]

Thank you so much ! I’m taking genetics and it’s one of the most feared courses in my UNI this video made made so much sense I can’t even explain how grateful I am you posted this !!

[@taylorguarino1555]

great video! 9 years later & still helping students :)

[@weird0.0]

This has been so helpful! Thank you!! Been struggling with this for awhile now, and somehow you made it so clear and simple in just a few minutes. Well done!

[@NottsAST]

KZbin is not letting me do a direct reply so I'll just post the answer: Epistatic alleles (or epistatic genes) determine whether a another gene is expressed or not. They may be dominant or recessive. Dihybrid means a cross between two individuals with two genotypes, e.g AaBb x AaBb or AABB x aabb. If it was just one gene locus it would be Aa x Aa or AA x aa for example, known as a monohybrid cross.

[@subarnasubedi7938]

You are my life saviour i dont have any words to express thanks a lot may god god bless u till the eternity

[@ChanTheAllan]

This video is very helpful. I was perfectly fine with epistasis until yesterday, when we had a revision lesson on epistasis with a substitute teacher (our actual teacher left the school after finishing the course with us). The teacher we had yesterday went through recessive and complementary epistasis fine and then, when she was going through dominant epistasis, she was describing recessive epistasis again and kept interrupting or talking over us when we tried to tell her why she was wrong. She got pretty much the whole class confused and disrupted my initial understanding of the concept.

[@dommy5642]

Love it.... THANKS much easy understood 🤗

[@mariabaptista-pt]

You re a fantastic teacher, thanks very much.

[@varsharavi5602]

This video really helped, thank you:) can you do a video about the page in the book "interactions between gene loci 2" with the coat colour in mice etc please? Thank you

[@paulathornley1453]

Hello thank yo so much for your help... Hope you don't mind me asking a question? How would you define the following- Dihybrid Epistatic allele To get the marks in the exam because I know OCR are very specific Thanks again

[@csillamaurnyi4595]

Great content, thank you!

[@nidakhan2025]

Very well explained. THANKYOU

[@hoperosalind8688]

great teaching resource!

[@mulecc]

That makes sense, thank you

[@curiouscat1487]

Thanks a whole lot

[@sciNobiH]

Thank youu so muchh

[@alevelsdemystified3410]

Great work

[@buseyikar]

Thank you !

[@SagarPatel-bf2sq]

Great video

[@esperanceuzabakiriho6206]

Hi there may i ask for an explanation on the cooperative epistasis?

[@Jess-kq4mb]

great video!!!

[@friedchicken7132]

I have a question sir. In the case of "A_bb", shouldn't the answer be "Blue" instead of "white", since A_bb would suggest "Mask white", therefore show "Blue"?

[@NottsAST]

Without hunting through the clip to find the bit you're asking about...I think you are saying that if it is bb then the recessive alleles would show up as white anyway, regardless of any masking effects

[@jamies798]

Great video thanks a lot

[@mulecc]

Thanks for your videos, very useful but I have a question if that's okay. If a question said how does epistasis reduce phenotypic variation? How would I world the answer? As in one gene will suppress the action of another one so even with different alleles of the second gene the same phenotype occurs?

[@NottsAST]

Yes, this is one of the lines in the book. Let's say you have alleles for red or purple leaves, depending on if it is hom dom, hetero or hom rec. Some of these phenotypes will NOT be expressed if they are hypostatic (under the influence of epistatic alleles), so they may all be white for example. Therefore less phenotypes than you would expect. Make sense?

[@TommyTVHoang]

Thank you very much!! :)

[@chaymaeeladak5526]

Thank you so much

[@Zouhairbsi]

Tnk u for it

[@chryskou8893]

I got almost everythink, except the part with the pink...can you explain me why please? Oh, and how doesn't A have any affection in bb?

[@NottsAST]

I'm not sure which pink bit you mean. I guess by the second part of the question, you mean why doesn't AA or Aa cause any change in the homozygous recessive bb? In questions about pigmentation, white is *often* a kind of blank colour, BB or Bb make a pigment but bb makes no pigment. So in dominant epistasis that inhibits the expression of the second allele pair, the inhibition produces "no colour" so it is also white, just like the bb will produce white anyway.

[@chryskou8893]

Ok, thank you very much!!!!

[@rohitmakwana7988]

At 7,15 the ratio has to be 12:3:1

[@ChanTheAllan]

Rohit Makwana He does correct the ratio, if you continue watching for a few more seconds.

[@whatislifeism]

Thankyou!!

[@joekoris1454]

why do you 'stick' with the colours AaBb and AaBb? how do you know to use them?

[@sakshiacharya8290]

god bless you

[@prettyrocker4514]

could you explain it for fruit colour of cucurbita pepo?

[@lihinilemon9597]

Thankssssssss

[@Mj-kl3rb]

I think you meant 12:3:1 not 12:2:1

[@MrMichael32940]

he changed it in his vid.....

[@Mj-kl3rb]

michael hogrefe haha oops, I should've finished the video.

[@TheShaam786]

whos watching this for tommorow?