For sweetie, some genetics help

[queenofthenile]

Here goes, sweetie. I really think you should learn this stuff for yourself, then you will feel more comfortable with the whole thing. At first it may seem like a lot, but I think I covered everything. I will try and explain the whole thing in simple terms. If anything confuses you, please don’t hesitate to ask. I’m starting from the beginning, assuming you have no prior knowledge of genetics. If you already know some of this stuff, please bear with me. I wanted to eventually type this all out for my website, so it might as well be now. I’m going to paste this in consecutive messages so that it will be less confusing.

All living organisms have a genetic code made of DNA (deoxyribonucleic acid). The DNA is made up of long sequences of “nucleic acids”. The DNA is then organized into units called chromosomes. All chromosomes come in pairs within somatic cells (all body cells except for the reproductive cells). The reproductive cells (sperm and eggs) only carry one copy of each chromosome. This is so that when the sperm and egg join, the resulting zygote winds up with two copies of each chromosome, which is the right number.

So every organism has two copies of each gene. These genes, however, can come in different forms, which have slightly different sequences of DNA. These forms, which are called “alleles” result from genetic mutation.

Alleles can interact with each other in different ways. The natural or “wild-type” allele is usually a dominant allele. This means that you only need one copy of the allele to mask the presence of other alleles. For instance, if a gerbil is Aa and the A allele is dominant, you will only see the A colour, not the a colour. This is because A is dominant over a. The a colour will only show up if there are two of them. The a allele would therefore be called “recessive”. All that means is that you need a pair of them in order for the genetic trait to show. Dominant alleles are usually noted by capital letters and recessive alleles by lowercase letters. In most cases, the wild-type or natural allele will be the dominant one. In coat colours, the only dominant allele that isn’t wild-type is the spotting allele.

There is also an unusual interaction known as co-dominance. This is when one allele doesn’t really mask the other allele. Neither allele is dominant, rather both alleles work together to give an altogether different colour. For instance, if the gene C is codominant with the Ch allele, then you can wind up with 3 different possible colours. You will get one colour when you have CC, a slightly different colour when you have CCh, and another colour with ChCh.

[queenofthenile]

So now that you know some of the genetics basics, here is the information pertaining to gerbil coat colours, alone:

The wild-type gerbil coat, agouti, has three bands. The top band is black, the middle band is yellow and the lower band is black. Several of the coat colours affect the banding pattern.

In gerbils, almost all of the coat colour genes come in only two alleles. (The exceptions are the C and E genes - which have three alleles). There are seven know coat colour genes in mongolian gerbils. They are:

A gene = this controls the colour of the belly and the a allele is recessive
A allele = the belly will be white
a allele = the belly will be the same colour as the back – many people call this a “self” gerbil

Ie: AA = white belly (agouti)
Aa = white belly because a is a recessive gene (agouti)
aa = the gerbil will have a coloured belly (black)


C gene = this is the colourpoint gene and so controls the distribution of pigment to the extremities. The C gene is an example of “co-dominance” because one copy of either the Cchm or Ch alleles will cause the coat to be slightly different, but not a colourpoint. You need two copies of either Cchm or Ch to give you a colourpoint gerbil
C allele = gerbil will have normal pigmentation
Cchm allele = with the presence of one allele, it causes the coat to be lighter when other genes are present (such as pp and ee). With the presence of two alleles, it causes the pigment to accumulate in the extremeties.
Ch allele = with the presence of one allele, it causes the coat to be lighter when other genes are present (such as pp and ee), more so than Cchm. With the presence of two alleles, you get a Pink-eyed white gerbil with a dark tail.

Ie: CC = normal distribution of pigment (agouti)
CCchm = coat lighter than normal (if the gerbil is ee or pp), otherwise the gerbil will appear the same
CCh = coat lighter than normal (if the gerbil is ee or pp), otherwise the gerbil will appear the same
CchmCchm = colour accumulates in the extremeties (colourpoint agouti)
CchmCh = colour accumulates in the extremeties, but is lighter (light colourpoint agouti)
ChCh = eliminates all colour except the tail (dark-tailed white)


D gene = this gene “dilutes” the colour of the coat. As far as I know, it is a recessive gene.
D allele = gerbil will be the normal, dark colour
d allele = the gerbil will be lighter coloured

Ie: DD = normal dark colour (agouti)
Dd = normal dark colour (agouti)
dd = diluted colouring (dilute agouti)


E gene = this gene controls the grey undercoat of the gerbil and so can cause gerbils to be golden, when the grey undercoat is not there. One of the alleles is also a colourpoint gene. The e allele is recessive and the e(f) allele is co-dominant when the other allele carried is e.
E allele = black lower band is present
e allele = black lower band is not present so the gerbil will have gold-coloured fur
e(f) allele = one copy of the gene will cause lightening of the fur when other genes are present (like e). When there are two alleles present, the gerbil will have gold-coloured fur concentrated in the extremeties due to a lack of the black lower band.

Ie: EE = black lower band present (agouti)
Ee = black lower band present (agouti)
ee = black lower band absent = golden gerbil (dark-eyed honey)
Ee(f) = black lower band present (agouti)
e(f)e(f) = black lower band absent with gold colour concentrated in the extremities (schimmel)
ee(f) = black lower band absent with gold colour slightly lighter than ee (light dark-eyed honey)


G gene = the gene controls the amount of yellow colouring in the fur. The g allele is recessive.
G allele = the yellow band is present
g allele = the yellow band is absent

Ie: GG = yellow band present (agouti)
Gg = yellow band present (agouti)
gg = yellow band absent (grey agouti)


P gene = this gene controls the colour of the gerbils eyes as well as the black bands on the hair. The p allele is recessive.
P allele = eyes are black and upper and lower bands are black
p allele = eyes are red and the upper and lower bands are grey

Ie: PP = black eyes and black banding (agouti)
Pp = black eyes and black banding (agouti)
pp = red eyes and grey banding (argente golden)


Sp gene = this gene controls spotting and is a dominant gene. A spotted gerbil will also have a white belly.
Sp = gerbil will have spotting and a white belly
sp = gerbil will not have spotting

Ie: SpSp = lethal combination, this fetus will be resorbed
Spsp = coat will have spotting and gerbil will have a white belly
spsp = no spotting

[queenofthenile]

Now that you know what genes the gerbil coat colours are governed by, here’s a list of all the possible colour combinations. Beside them is the short-hand of the recessive genes that you know that they have. They may also be carrying other recessive, but you won’t know this unless you are sure of their parentage.

White bellied colours:
Agouti

Argente Golden
(pp)

Argente Cream
(Ch pp)

Topaz
(Cchm pp)

Grey Agouti
(gg)

Ivory (cream)
(gg pp)

Dark-eyed Honey
(ee)

Yellow Fox (red-eyed)
(ee pp)

Polar Fox
(ee gg)

Cream Fox (red-eyed)
(ee gg pp)

Spotted gerbils
(Spsp)


Solid colours:
Black
(aa)

Slate
(aa gg)

Lilac
(aa pp)

Dove
(aa Ch pp)

Sapphire
(aa Cchm pp)

Red-eyed White
(aa gg pp)

Nutmeg
(aa ee)

Red Fox
(aa ee pp)

Pale Red Fox
(aa Ch ee pp)

Silver Nutmeg
(aa ee gg)

Schimmel
(efef)

Red-eyed Schimmel
(efef pp)


Colourpoints/Himalayans:
Colourpoint Agouti
(CchmCchm)

Colourpoint Grey Agouti
(CchmCchm gg)

Burmese
(aa CchmCchm)

Siamese
(aa CchmCh)

Colourpoint Nutmeg
(aa CchmCchm ee)

Colourpoint Silver Nutmeg
(aa CchmCchm ee gg)

Dark-tailed White
(ChCh)

Very Dark-tailed White
(aa ChCh)

Pink-eyed White
(ChCh pp) – no matter what other recessives are present

[queenofthenile]

Now how to figure out what the offspring will look:

The coat colour genes are are not “linked genetically”. This is a fancy term meaning that picking one gene will not influence what you pick for the next gene. Essentially, all seven genes exist on seperate chromosomes. This is very important because it actually makes the genetics much easier.

Lets pretend the two genes are two different types of candies. You have jelly beans (gene A), which come in black and white (the alleles), and tictacs (gene B), that come in green or orange (the alleles). Pretend that you have the tictacs in one hand and the jelly beans in another. Lets say Evan pics the green tictac from your hand, this will not affect which jelly bean he will take. He is still free to choose either the black or white jelly bean. This is like genes that are not genetically linked. Choosing one of the genes does not influence the choosing of the other gene. It makes the entire process random.

If the genes were linked (ie: on the same chromosome), you would just smush one of the tictacs into one of the jellybeans. Everytime you picked one of the jellybeans, you would also be picking the tictac that was associated with it. This would be an analogy of genes on the same chromosome, and so the whole process isn’t random. That makes genetics calculation much more difficult, because if the genes are far apart, they will be picked together a certain percentage of the time and will be picked seperately the rest of the time. (I really hope that my candy analogy hasn’t totally mystified you).


Now that you know that the genetics is greatly simplified you can give a big sigh of relief. Since this is the case, figuring out the genetics of the offspring is a simple as using a “punnet square”. You could also just use a genetics calculator, but I’m weird and like doing it by hand.

Here’s what a punnett square looks like:


First you start by figuring out what are the possible gene combinations that each parent can contribute to their offspring. When the sperm and eggs are being produced, only one copy of each chromosome goes to the gamete (egg/sperm). Since all organisms have two copies of each chromosome, the gamete will either get chromosome A or chromosome B. Since this process is random, you will get A 50% of the time, and B the other 50% of the time.

Lets take a female gerbil that is Aa for example. 50% of the time the egg will get A and 50% of the time the egg will get a.

If you mate her with an Aa male, then 50% of the time the sperm will get A and 50% of the time the sperm will get a.

Then you just drop the possiblities into the punnett square:


Once you do that, you can put the possibilities from each parent together like so:

So this cross will give you ¾ agouti and ¼ black.


When you start to work with more than one gene, it gets more confusing. A good rule is to count the number of genes of the parent that have two different alleles. That number is then called "n". Then the number of possible gametes that the parent will produce is 2ⁿ. This just reminds you how many combinations that must go into your punnett square.

For instance, if the parent has Aa Pp, you have two genes that have two different alleles. This means the number of possibilities is 2ⁿ = 2² = 4 (The gene possibilities are AP, Ap, aP, and ap)

If the parent is aa Pp, you only have one gene that has two different alleles. In the case of the a gene, the parent will always be giving an 'a' to their offspring, so there isn’t actually a choice happening. So the number of possibilities is 2ⁿ = 2¹ = 2 (The gene possibilities are aP and ap)


Now lets try the punnett square again using both of these parents:

So you would get 3/8 agouti, 3/8 black, 1/8 argente golden and 1/8 lilac.

[queenofthenile]

Now how to figure out what the offspring will look:

The coat colour genes are are not “linked genetically”. This is a fancy term meaning that picking one gene will not influence what you pick for the next gene. Essentially, all seven genes exist on seperate chromosomes. This is very important because it actually makes the genetics much easier.

Lets pretend the two genes are two different types of candies. You have jelly beans (gene A), which come in black and white (the alleles), and tictacs (gene B), that come in green or orange (the alleles). Pretend that you have the tictacs in one hand and the jelly beans in another. Lets say Evan pics the green tictac from your hand, this will not affect which jelly bean he will take. He is still free to choose either the black or white jelly bean. This is like genes that are not genetically linked. Choosing one of the genes does not influence the choosing of the other gene. It makes the entire process random.

If the genes were linked (ie: on the same chromosome), you would just smush one of the tictacs into one of the jellybeans. Everytime you picked one of the jellybeans, you would also be picking the tictac that was associated with it. This would be an analogy of genes on the same chromosome, and so the whole process isn’t random. That makes genetics calculation much more difficult, because if the genes are far apart, they will be picked together a certain percentage of the time and will be picked seperately the rest of the time. (I really hope that my candy analogy hasn’t totally mystified you).

Now that you know that the genetics is greatly simplified you can give a big sigh of relief. Since this is the case, figuring out the genetics of the offspring is a simple as using a “punnet square”. You could also just use a genetics calculator, but I’m weird and like doing it by hand.

Here’s what a punnet square looks like:


First you start by figuring out what are the possible gene combinations that each parent can contribute to their offspring. When the sperm and eggs are being produced, only one copy of each chromosome goes to the gamete (egg/sperm). Since all organisms have two copies of each chromosome, the gamete will either get chromosome A or chromosome B. Since this process is random, you will get A 50% of the time, and B the other 50% of the time.

Lets take a female gerbil that is Aa for example. 50% of the time the egg will get A and 50% of the time the gene will get a.

If you mate her with an Aa male, then 50% of the time the sperm will get A and 50% of the time the sperm will get a.

Then you just drop the possiblities into the punnet square:


Once you do that, you can put the possibilities from each parent together like so:

So this cross will give you ¾ agouti and ¼ black.


When you start to work with more than one gene, it gets more confusing. A good rule is to count the number of genes of the parent that have two different alleles. That number is then calle "n". Then the number of possible gametes that the parent will produce is 2ⁿ. This just reminds you how many combinations that must go into your punnet square.

For instance, if the parent has Aa Pp, you have two genes that have two different alleles. This means the number of possibilities is 2² = 4 (The gene possibilities are AP, Ap, aP, and ap)

If the parent is aa Pp, you only have one gene that has two different alleles. In case of the a gene, the parent will always be giving an a to their offspring, so there isn’t actually a choice happening. So the number of possibilities is 2¹ = 2 (The gene possibilities are aP and ap)


Now lets try the punnet square again using both of these parents:

So you would get 3/8 agouti, 3/8 black, 1/8 argente golden and 1/8 lilac.

[sweetie]

Wow........ You took a lot of time and energy. THANK YOU. I will print this out and work really hard to internalize this. Heck, it's the least I can do after you did all this. Thanks Queenie. You are the best.

[RW]

This is nice work--very understandable and concise--and cleared up a couple of points I was a little fuzzy on. Good job.

RW

[queenofthenile]

RW, was there anything that I wrote that was confusing? Maybe the candy analogy for linked genes ? When I re-read it, that part sounds kind of funny .

[RW]

I'm not a breeder and I don't claim to be any kind of genetics expert, but I've done some reading, so I have a grasp of the basics. I thought your explanation of general genetics was good. I've been a little confused about the different effects of Cchm and Cch, but I think I've got it straight in my mind now, thanks to you.

The candy analogy made perfect sense to me.

BTW, I printed it to have for future reference, too.

Oh, and Punnett has 2 t's. I didn't know that until I looked it up. According to one site, the Punnett Square was named for the British geneticist Reginald Punnett. Yeah, I have a trivia thing...and a spelling thing...

RW

[queenofthenile]

Arrrgghh! I knew that! How could I spell it wrong each and every time??!!

[RW]

Poor old Mr. Punnett must be rolling in his grave! ;D

RW