Hi there!
I don't know if you know about alleles etc. A gene has two alleles it could be "BB", "bb" or "Bb" (the letter doesn't matter, it could be any letter of the alphabet). So say if brown was dominant and white was recessive in horses, capital "B" would be the dominant brown gene and lowercase "b" would be recessive white. Dominant requires only one allele of its kind in the gene to show physically, so it could be "BB" or "Bb" and both would be brown. Recessive requires two of its kind to show physically which would be "bb". "Bb" holds a brown allele and a white allele, so the horse would be brown, split to white - showing only brown and only "holding" the gene for white.
As Whiteface is recessive their gene would be for example "ww", if you bred two Whitefaces, both their genes would be "ww" so all of their chicks would be "ww" (whiteface) as they do not carry the gene for non-whiteface. However, if you were to breed whiteface "ww" with non-whiteface "WW" you would get 0 whiteface chicks. If you bred whiteface "ww" with a non-whiteface split to whiteface "Ww" you would get 50% whiteface chicks.
The sex-linked genes are harder to work out. Cockatiels can only inherit them physically from the father. So you could only get cinnamon chicks from Finn if he is split to Cinnamon. If a female is cinnamon and the male is not or is not split to it, then none of the chicks will be cinnamon. However, if the male does carry the Cinnamon gene, then his chicks could inherit it. If this was the case, if the female wasn't cinnamon, then all the cinnamon chicks would be female, but if the female also held the cinnamon gene, then the cinnamon chicks could be male or female. Its so complicated. I guess you already know that only male cockatiels can be split to sex-linked genes, if females have a sex-linked gene, they will show it.
So, as a summary: if the female is whiteface, then all of the chicks will be whiteface ; if Finn is not split to Cinnamon, then none of the chicks will be Cinnamon. My cockatiel Pika, turned out to be split to Cinnamon when we bred him, so there's a chance yours is as well.
I don't know if any of this really makes complete sense. It took ages for me to get my head round it, after loads of research. If you are doing Biology at school, the subject of inheritance would probably help.
If you have any questions please do ask, because this subject is extremely confusing and I probably didn't explain it very well.

If you haven't already, I'd recommend watching some videos on genetic inheritance.

 

Understanding the explanation of sex-linked traits was quite complicated. I had to re-read it a few times. I found the initial part to be quite clear because I did finish Biology, and I’m familiar with the Punnett square. However, I am not entirely certain about the nature of the “splits” you mentioned. When I inquired about a white-faced Grey at the breeder, I was expecting to receive a White-faced Grey but, he turned out to be a split between a White-faced Grey and a Pearl.
To determine if Finn possessed the Cinnamon gene, I am unsure how to identify it. He does not appear to have the characteristic warm tint associated with the Cinnamon gene; instead, he exhibits the typical Grey, with WF + Pearl along his back.
Attached is a photograph for your reference.
Before concluding, I would like to mention that some of his tail feathers are yellow. While I have not done any extensive research on this trait, it is possible that you could potentially any other hints to what else he could have been bred with?

Thanks for your response by the way!

 

Understanding the explanation of sex-linked traits was quite complicated. I had to re-read it a few times. I found the initial part to be quite clear because I did finish Biology, and I’m familiar with the Punnett square. However, I am not entirely certain about the nature of the “splits” you mentioned. When I inquired about a white-faced Grey at the breeder, I was expecting to receive a White-faced Grey but, he turned out to be a split between a White-faced Grey and a Pearl.
To determine if Finn possessed the Cinnamon gene, I am unsure how to identify it. He does not appear to have the characteristic warm tint associated with the Cinnamon gene; instead, he exhibits the typical Grey, with WF + Pearl along his back.
Attached is a photograph for your reference.
Before concluding, I would like to mention that some of his tail feathers are yellow. While I have not done any extensive research on this trait, it is possible that you could potentially any other hints to what else he could have been bred with? View attachment 98022

Thanks for your response by the way!

That's great, I'm glad you understand all of that stuff. Honestly, I find it the most interesting part of biology! 😅
Your bird is a Whiteface Pearl, he is not split to pearl, if he was, he would not show the pearls. If he is showing yellow in the tail, it might be a stain, because the whiteface mutation removes any yellow + red pigmentation from the feathers. He could be split to Lutino, Cinnamon, Yellow-cheek which are sex-linked. Or he could be split to Pied and other mutations. You can't see Lutino, Cinnamon or Yellow-cheek, when they are split. Split Pied can be identified by some white feathers on the nape of the bird.
Not my photo!

I'll show you a photo of my male cockatiel. He's a Whiteface Pearl Pied. He's always been extremely lightly pearl, even when he was younger he hardly was pearled, I only figured out that he was recently! He paired with a female Pearl Pied. From the chicks, we found out he was split to Cinnamon and Lutino, as he has had two chicks that show cinnamon and one that shows lutino. We also found out that the female was split to whiteface as several chicks came out as whiteface!

At first glance you wouldn't know he has pearl, cinnamon and lutino in him!
So you see, until you breed him, you probably won't know what mutations he holds. To be honest I found it exciting finding it all out!

 

Hmm..lutino is used to make the white face mutation so yeah I guess that does explain it. Thanks for clarifying the split part, I thought that just meant it had a smaller amount of it, or it was losing it in the blood line or something. Your bird is gorgeous by the way!! I really appreciate your help, defiantly cleared a lot up for me.