genetics, do explain!

[E13]

Copied from my nursing book for ease!

Test mating with a homozygous recessive animal (example of black, BB or Bb, and chocolate, bb, labradors) to determine whether black lab is BB or Bb - mate with bb:
If lab is BB then all offspring are black (Bb).
If lab is Bb...

Bb x bb = Bb, Bb, bb or bb offspring.

If the black produces 7 black pups you can be 99% sure it is BB (obviously any choc pup means it's Bb).

Test mating with a known heterozygous carrier (using black/choc example though this is normally for 'unseeables' like disease); mate the unknown black lab to a known Bb.

If lab is Bb: Bb x Bb = BB, Bb, Bb, bb offspring.

16 black puppies must be produced to be 99% sure dad is BB not Bb.

I understand this; what I don't understand is the last bit, about needing 7 (or 16) black pups to be 99% sure dad is BB. I understand there's a 50% or 75% chance the pups will be black, but where do those numbers come from??

 

[s4sugar]

Have you ever used a punnett square?

Most people work on the premis that you cannot prove not carrying a recessive but producing one proves it is carried. Certainly seven & 14 are not large enough samples 20 & 50 might give a 99% result.
The odds on gender are 50:50 but I know of three litters of twelve that were same sex.

The 7/14 numbers are theoretical and I remember them from uni -many years ago - but they have been disproved.

 

[satinbaze]

Far easier way to determine colour genetics is to have the dog colour tested. One quick cheek swab!!!!!!

 

[E13]

Have you ever used a punnett square?

Most people work on the premis that you cannot prove not carrying a recessive but producing one proves it is carried. Certainly seven & 14 are not large enough samples 20 & 50 might give a 99% result.
The odds on gender are 50:50 but I know of three litters of twelve that were same sex.

The 7/14 numbers are theoretical and I remember them from uni -many years ago - but they have been disproved.

I saw the punnett square in my book, and I understand about the different offspring it can produce... So these 7 and 16 numbers, you say they are theoretical, where did they come from? I understand that if you continually have black pups it increases the likelihood of dad being BB, but I don't get there numbers

 

[Vicstress]

Copied from my nursing book for ease!

Test mating with a homozygous recessive animal (example of black, BB or Bb, and chocolate, bb, labradors) to determine whether black lab is BB or Bb - mate with bb:
If lab is BB then all offspring are black (Bb).
If lab is Bb...

Bb x bb = Bb, Bb, bb or bb offspring.

If the black produces 7 black pups you can be 99% sure it is BB (obviously any choc pup means it's Bb).

Test mating with a known heterozygous carrier (using black/choc example though this is normally for 'unseeables' like disease); mate the unknown black lab to a known Bb.

If lab is Bb: Bb x Bb = BB, Bb, Bb, bb offspring.

16 black puppies must be produced to be 99% sure dad is BB not Bb.

I understand this; what I don't understand is the last bit, about needing 7 (or 16) black pups to be 99% sure dad is BB. I understand there's a 50% or 75% chance the pups will be black, but where do those numbers come from??

The ratio is 3:1 so it's a 3/4 chance the pup will be black with a Bb male. Based on this ratio, 20 puppies would need to be born (16 of those being black) to prove the ratio as the odds are for the first few 'sets' of 4, they'd be black anyway....agree that really you'd need more than 20 puppies to prove that theory but that's scientists for you

 

[E13]

The ratio is 3:1 so it's a 3/4 chance the pup will be black with a Bb male. Based on this ratio, 20 puppies would need to be born (16 of those being black) to prove the ratio as the odds are for the first few 'sets' of 4, they'd be black anyway....agree that really you'd need more than 20 puppies to prove that theory but that's scientists for you

Maybe I'm looking at this too late but I'm still a bit I'm not thick, honest!

I get the 3/4 chance of being black with Bb dad, and I get that this may not be apparent in a small number of pups as they could all be black. But surely one single chocolate pup proves the dad is Bb; however, only black pups means the dad could either be BB or Bb...

Looking at the dad x bb pairing... there's a 50% chance pup is black or choc. Why does it have to be specifically seven black pups to be almost certain dad is BB? Because he could still have a choc pup in the future... Is it because seven is a large enough number of black pups that the probability of 50% black 50% choc is disproved, meaning that dad being BB is almost certain? Where on earth does the number seven come from??


I have a feeling once I understand this it will be dreadfully simple