INHERITANCE - AQA A LEVEL BIOLOGY + EXAM QUESTIONS RUN THROUGH
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- เผยแพร่เมื่อ 30 ก.ค. 2024
- In this video, I explain ALL of the content required for the "Inheritance" section for AQA A Level Biology. This includes: genotype + phenotype, concept of heterozygotes/homozygotes, multiple alleles, monohybrid crosses, test crosses, dihybrid crosses, codominance autosomal linkage, sex linkage, epistasis and the chi-squared test. Time stamps are in the comments.
I also go through a few exam questions and explain their mark schemes.
All the content in this video crosses over with other exam boards.
Please leave a comment if you have any questions, I'll be more happy to answer them!!! :)
Image taken from:
biology.arizona.edu
01:03 = Genotype + Phenotype
01:34 = Multiple Alleles
02:15 = Homozygotes, Heterozygotes, Dominant + Recessive Alleles
05:20 = Codominant Alleles
06:32 = Monohybrid Crosses
10:22 = Test Crosses
11:27 = Dihybrid Crosses
15:03 = Autosomal Linkage
16:37 = Sex Linkage
19:12 = Epistasis
22:03 = Chi-squared Test
28:50 = Exam questions and mark schemes
You are just great
When a TH-cam teaches you more than school 😂
frrr
i think you might have just saved my entire biology a level grade with these videos, thank you so much!
You're so welcome! :)
Do you think you could go through an exam paper? It's so helpful when you show how to apply the knowledge to questions
I cannot thank you enough for these videos, you explain them in such an amazing way, I finally understand genetics :)
You make some amazing videos and they really do help, especially during lockdown. Please keep them coming, I cannot thank you enough!! :)
Thank you so much, it means a lot! :)
Thank you for this!! I was looking for something on chi-squared and this was simple and easy to get.
Thank you, so glad I could help!
My teacher went on and on about this for 2 x 2 hour lessons and you’ve managed to teach me this in 40 minutes lol why do I even go to school at this point
so truee
Thank you so much, I’ve got my unit 3 a level in 2 days. Needed this👍🏼
Good luck!!!
ur channel has saved my life
Thank you so so much for this! So helpful! Honestly really appreciated! You should keep doing more topics- they are so clear and easy to understand! Have you done all the topics for aqa? Thank you!
Hi! Yes, I have done all the topics for AQA :)
Wow you really made this chapter so much easier to understand!
So glad I could help!
Thank you so much, these videos help a lot. What would you recommend to do after watching these videos
thank you so much, this was so useful!💕💕💕
That is a great video. I am a student in Year 9. 😊
Thank you, need this for my A level paper 2 at 9
you are amazing. thank you sooo much
these videos are really good
Thank you!
Absolute god send
Hi could I please double check that the one with half the offsprings having a recessive phenotype means the unknown is heterozygous dominant?? For 11:26
Sorry for taking so long to reply! The unknown genotype is being crossed with a homozygous recessive individual here (let's call it "cc"). If you draw out a punnett square, then you will be able to see that when you cross it with a heterozygous ("Cc") individual, half of the offspring have a recessive phenotype (cc). Hope this makes more sense :). If all offspring had a recessive phenotype, the unknown would be homozygous recessive
This is amazing tysm
Perfect Vid by the way 🤩 👌 Have you included the Hardy Weinsberg equation ?
Hi! The Hardy-Weinberg equation is covered in my "Population Genetics" video :)
For the last question (38:40), could the parents not also be XfXf and XfY? why does the father have to have a dominant allele? I tried to draw the punnet square and its not making sense :(
Hi. That genotype isn't possible for the father because the question says that there are female offspring with slow feather production, represented by capital F. As females have XY chromosomes here (different to humans!), the X chromosome must be inherited from the Father , and the Y inherited from the Mother, so the Father must have a dominant allele. Hope this makes sense? :)
@@AlevelBiologyHelp How would there be 2 male offspring with rapid feather production though, if the male parent has a dominant allele
@@CL-qs7gg Because the offspring would've inherited one recessive allele from the father (there is a 50% chance of this as the Father is heterozygous), and one from the mother :). I hope this makes sense
For the last question I tried drawing a dihybrid cross for it and it just doesn’t seem to work? Even with the answers of XFXf and XfY against each other it just doesn’t seem to make two males with rapid feather production and two females with slow feather production. Am I not supposed to use a cross for this?
Hi! Crosses are there to give the probability of each possible genotype/phenotype, so it doesn't necessarily mean that each offspring will have each phenotype displayed from the results of the cross. In one case, all the offspring could have the same phenotype. As there were two females with slow feather production, this means that the Father must be heterozygous and the Mother must have the recessive allele for slow feather production as females have the sex chromosomes XX, so one allele must be inherited from each parent. We know that the Father isn't homozygous recessive as the male offspring have rapid feather production. Hope this helps :)
A level Biology Help is it the other way around in this case like you put that females have XX but for chickens here the females have XY?
@@Mozzie7920 Yes, it is the other way round to what I put in my previous reply, sorry!
A level Biology Help I understand why the female parent has to be XfY but I’m not understanding why the father with XX has to be heterozygous, like why can’t he be XFXF instead of XFXf?
@@Mozzie7920 If the Father was XFXF, then it would be impossible to have male offspring with rapid feather production, as that comes from a recessive allele (two copies are needed for expression)
at 21:56 you said "aa" shows epistasis to "b" allele...but doesn't it also show epistasis to the B allele, as it's masking both agouti and black phenotypes?
Yes it does!
thankyouuuu for thisssssssss
heyooo, I might be wrong but at 35:25 I don't see how chicken 5 is XfY, when in the pedigree diagram chicken 5 is a shaded circle, which means it's a female with rapid feather production. Same for Chicken 7.
rapid feather production is lower case f so 5 would be XfY and then because 7 is not shaded, it can be homozygous dominant or heterozygous as slow feather is dominant
Would these definitions be correct to answer a definitions question in the exam?
Yes :)
@@AlevelBiologyHelp Thanks so much!
hi just wondering how would you know if the question was autosomal. Would the question tell you? thankyou and really helpful video :)
Yes, the question would tell you if it's autosomal or sex-linked 😊
on 13:14 i don't understand why they're the possible gametes
dw i get it now
and how do you think year 13s will get their final grades
Hmm...I'm not sure. Nothing has been decided yet for definite, other than the fact that the grades will be teacher-assessed. There is also the probability of "mini-exams" , but nothing is final yet ☺️
So, does each gamete have one allele in?
Yes, each gamete has one allele for every gene. :)
at 12:52 how did u work out that they were all RrYy?
Hi, so the gametes for the round green are RY (the only type as it is homozygous for each gene) and the wrinkled yellow gametes are ry (same reason). If you combine these (fertilisation) you get all RrYy. No other genotypes are possible because the parents are homozygous for each gene :)
@A level Biology Help how would you know if they are homozygous or heterozygous? Is it because they RRYY which are same genes so they are homozygous.
You’re a star 🫶🏾
In the second last question you said the female child was XfY but it should have been XfXf if she was affected which isn’t possibke
Hi! The question says that female chickens are XY, which is opposite to humans, so it can get confusing! This means that a female only needs one rapid feather production allele to have the phenotype. This allele is recessive, so it must have been passed on through the father (1) who must be heterozygous. Hope this makes more sense. :) Xx
Why would chicken 7 in question b have 2 X chromosomes if it’s a a male? (and why does chicken 5 have XY chromosomes if it’s a female)
Hi, so chickens are actually different to humans (xx-female xy-male). In chickens, XX is a male and XY is a female! It says that at the start of the question so make sure that you read it properly! :)
@@AlevelBiologyHelp Thank you so much for the clarification!
would this be fine for edexel?
Hi! Yes, the content is basically the same :)
better than skl lmao
Is this IGCSE or GCSE?
Hi, this is A Level 👍