INHERITANCE - AQA A LEVEL BIOLOGY + EXAM QUESTIONS RUN THROUGH

🧬 AQA A Level Biology - Inheritance | Full Topic Explained + Exam Questions

In this video, I go through all the content required for the Inheritance topic in AQA A Level Biology. It’s packed with clear, concise explanations—perfect for revision or learning it from scratch.

I also walk through exam-style questions, showing how to break them down and apply mark scheme logic to get full marks.
⏱️ Timestamps are in the comments to help you jump to what you need.

✅ Includes explanations of:

Genotype and phenotype

Homozygous and heterozygous alleles

Monohybrid crosses

Dihybrid crosses

Codominance

Multiple alleles

Test crosses

Sex linkage

Autosomal linkage

Epistasis

Chi-squared test for genetic ratios

🎯 Ideal for:

AQA A Level Biology students

OCR/Edexcel students (some crossover)

Genetics revision

Exam prep and question practice

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Image taken from:

[AlevelBiologyHelp]

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

[sophieg]

i think you might have just saved my entire biology a level grade with these videos, thank you so much!

[lillyclark]

Do you think you could go through an exam paper? It's so helpful when you show how to apply the knowledge to questions

[loisdimmock]

When a YouTube teaches you more than school 😂

[hollybrookes]

I cannot thank you enough for these videos, you explain them in such an amazing way, I finally understand genetics :)

[Gina-uyzn]

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

[yasinkhan]

You make some amazing videos and they really do help, especially during lockdown. Please keep them coming, I cannot thank you enough!! :)

[jadethatcher]

Wow you really made this chapter so much easier to understand!

[simransangha]

Thank you for this!! I was looking for something on chi-squared and this was simple and easy to get.

[lukejones]

Thank you so much, I’ve got my unit 3 a level in 2 days. Needed this👍🏼

[aaliyahpatel]

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!

[kingslayer]

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 :(

[ng]

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

[kamkam]

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.

[pissvib]

at 12:52 how did u work out that they were all RrYy?

[elliesmith]

Thank you, need this for my A level paper 2 at 9

[legendlegend]

on 13:14 i don't understand why they're the possible gametes

[Mozzie]

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?

[linasaadani]

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?

[everpresent-cpcs]

really good video! for the cross between the two heterzygous mice I dont think the phentoypes are correct, since AAbb would result in albino mice since the expression of gene A is masked by the abscence of melanin (coded for by dominant allele B). And surely aaBB would result in black mice?