Friday, May 20, 2011

Some scenarios for inbreeding, line breeding and outcrossing


This article is a continuation of "To inbreed, line breed, or outcross?"






RATTUS FAMILY TREE

Look at the family tree below. If you’re new to breeding, choose your foundation pair (‘P’) wisely. From them, you will be able to build your line (‘family tree’) within a few months.





So your problem now is that you’re not sure which breeding method to use? Here are some scenarios to help you decide…


INBREEDING

Scenario 1:

One day, two wild rats wandered into your home. You adopted them and wanted to breed them. So you have Parent A and B, both black (aa) – not knowing what surprises lie hidden within their genes.



What you DO NOT KNOW is that A carries albino (Cc), and B is a homozygote non-albino (CC).



C
C
C
CC
CC
c
Cc
Cc


From this cross, we get 50% homozygote non-albino (CC) and 50% carriers (Cc).



They produced a first generation litter (‘F1’) of all black, half of which is albino carrier, leading you to the false presumption that they only carry black.

Now, you want to find out what recessive genes they carried, so you will inbreed Parent A with one of the F1 offsprings which happened to carry albino. So here’s the cross:



Parent A (Cc) x F1 carrier (Cc)


C
c
C
CC
Cc
c
Cc
cc

From this cross, we get 25% non-albino (CC), 50% carriers (Cc), and 25% albino (cc).

You were baffled how an albino pup emerged in the litter! This is because the inbreeding process has revealed to you that there is actually an albino recessive gene already in the line of your black wild rats!





Scenario 2: (Using the same rats as above)

You noticed that one of the F1 offspring actually has a nice deep black color. Parent B also has the same nice deep black coloration. They both had this nice trait so you paired them, and eventually produced a litter with nice deep black identical to the inbred parents!





LINE BREEDING

Look at the family tree above. You bred a pair of hooded rats as your foundation parents (P). They had a litter of four, which were later divided into two breeding sibling pairs. As they produced more descendants, you notice that the family tree divides into different branches of not so closely related relatives. This is what we call a ‘line’.

Your goal was to produce a hooded rat with a perfect saddle or spine. From your different lines of hoodies, you found an ideal pair which has the best traits to help you achieve your goal (aunt and nephew).

Since these related rats came from the same ancestors, you are sure that you’ll always get the same hooded pattern with little variation.





OUTCROSSING 
(Using the same hooded rats in line-breeding as example)

So by now you decided you want variation in your hooded rats. There were originally only black hooded rats (aaPPhh) with you, but now you wanted to produce amber rats (AApphh). Please also read ‘Modifying agouti and black’.

Amber is agouti based; agouti-based colors are dominant over black-based colors. The amber color is caused by the pink-eye dilution gene (P-locus), which slightly affects red/yellow pigments. So how are you going to produce amber rats? Here’s a map:



#1 First, you need to outcross one of the ‘black’ hooded rats (aa) with an ‘agouti’ rat (AA). We get 100% agouti carrying black.

Parent A (aa)     x     Parent B (AA)


A
A
a
Aa
Aa
a
Aa
Aa




#2 Next, from the result of the cross above, we breed the agouti carrying black (AaPP), with a rat that has pink-eye gene (e.g. champagne 'aapp').


Parent A (AaPP)     x     Parent B (aapp)

Using a genetics calculator to compute the cross above, we get:

  • AaPp (50%) - agouti carrying black and pink eye dilute
  • aaPp (50%) - black carrying pink eye dilute




#3 Finally, to get amber, we resort to inbreeding by crossing sibling to sibling (see table in #2).


Parent A: AaPp     x    Parent B: AaPp

Using a genetics calculator to compute the cross above, we get:

  • AAPP (6.25%) - agouti
  • AAPp (12.5%) - agouti carrying pink eye dilute
  • AApp (6.25%) - amber
  • AaPP (12.5%) - agouti carrying black
  • AaPp (25%) - agouti carrying black and pink eye dilute
  • Aapp (12.5%) - amber
  • aaPP (6.25%) - black
  • AAPp (12.5%) - agouti carrying pink eye dilute
  • aapp (6.25%) - champagne

From the final cross, it is possible to get 18.75% amber, 6.25% champagne, 6.25% black and 68.75% agouti!



Punnett Square Calculator

If you need some help making crosses, here is a free and useful tool to help you calculate the end result. Click here.
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