color mutation inheritance in snakes, a question

[regius]

I breed snakes and work mainly with color and pattern mutations for the pet trade. I’m having difficulty understanding the inheritance of a trait I’m working with. I’ll call that trait “B”. I’m working with a small sample size but I think the following are true:

 

Normal male x B female gives B females and normal males VERY RARELY a B male

 

B male x normal female gives B females never a B male

 

B male x B female gives B females and B males, no normal types (this is based on one breeding)

 

About 60 B animals have been produced, only 5 of these have been males (all produced for B x B breedings)

 

A B male has never produce a B male when bred to a normal female.

 

Snake sex chromosomes: males are ZZ and females ZW

 

Anybody have any ideas?

[Moontanman]

I bred fishes, color is often associated with sex. One of the easiest fish to bred is gambusia, the males will turn up black or mostly black in one out of a variable number but in most environments it's 20 or 30 to one (I think) stressed environments produce more but when you breed for the trait it almost never turns up in females and what few black females it does turn up in often die of tumors. I would think your trait "B" is sexually transmitted and your "B" males are either sexual mix ups or not really genetic males.

 

What species are you working with?

[Physicsfan]

B is a sex linked character(you might have known this already).

By your 1st statement, I can conclude that B is a recessive trait on the Z chromosome(not on the W chromosome because there are B males too).

I think you know this already too. If it was dominant then the males would have been B too.

this also explains your second and last but one statement because a normal female would have a dominent allele on the Z chromosome. so all the males will

have the dominant allele and hence be normal. but if the offspring is a female, it will always have a Z chromosome with recessive allele and so it will be a B female.

 

the third statement is also explained and it will always be true because the cross is between Z'Z' and Z'W.(By Z' i mean recessive allele bearing chromosome).

 

I hope this has been of help.

Edited June 11, 2010 by Physicsfan

[regius]

B is a sex linked character(you might have known this already).

By your 1st statement, I can conclude that B is a recessive trait on the Z chromosome(not on the W chromosome because there are B males too).

I think you know this already too. If it was dominant then the males would have been B too.

this also explains your second and last but one statement because a normal female would have a dominent allele on the Z chromosome. so all the males will

have the dominant allele and hence be normal. but if the offspring is a female, it will always have a Z chromosome with recessive allele and so it will be a B female.

 

the third statement is also explained and it will always be true because the cross is between Z'Z' and Z'W.(By Z' i mean recessive allele bearing chromosome).

 

I hope this has been of help.

 

OK, we're on the same page but here's something I don't understand. How can a B female (defective Z, normal W) make a female baby with the trait? she can only give defective Z and normal W. The father can provide only normal Z. Females are only coming from the father's normal Z and the females normal W. These should look normal.

 

All breedings with a B parent produce only B females, never a normal female.

[Physicsfan]

that could have been because the male might have been a heterozygous dominant(ZZ').

 

does the normal male x B female combination always give a B female ?

[regius]

that could have been because the male might have been a heterozygous dominant(ZZ').

 

does the normal male x B female combination always give a B female ?

 

no, the male was normal and didn't have any B in his background. Male normal x female B always makes all female B and normal looking males.

[Physicsfan]

the only way this combination can give such results is that the W chromosome of females also has a recessive allele for trait B, or a dominent allele for normal.

notice that any combinations with B females never gives a normal female. Normal

females are those which have the dominent allele, and cannot be bred from B females because the recessive allele on W chromosome cannot be replaced.

the genotype for a B female can be Z'W' or ZW' in either case im sure the B trait will be expressed because the expression of alleles on Z and W chromosomes are independant of each other.you may wonder about Z'W. im not sure of this either. you probably used pure B females, the ones with recessive allel on W, in the first combination.

 

im not able to find a better idea. do you have a suggestion or more breeding info which i can use?

 

-always glad to be of help to you

[dttom]

You said B male crossed with normal female got B female and normal male, so just label this B female as B1.

And B female crossed with normal male got B female and normal male, so this B female is B2, normal male as N2.

First, when N2 is inbred, will you have 25% B male in progeny?

Second, when you talked about B male crossing B female, you are using B1 or B2? If you are using B1 I may have an idea...

1) When a female got an affected W' or Z' or both, she expresses B trait.

2) B male occurs as Z'Z'.

[Physicsfan]

Second, when you talked about B male crossing B female, you are using B1 or B2?

both would give the same results,always.

 

First, when N2 is inbred, will you have 25% B male in progeny?

how would you do that?

Edited June 16, 2010 by Physicsfan

[dttom]

both would give the same results,always.

 

 

how would you do that?

 

Oh, sorry, you can't do that, then what about breeding them with normal female? Will this get 50% female B trait?

 

Because the information about crossing of B trait male and B female is based on single breed, it is not confident enough to be included in consideration.

The following is based on your first two statements:

1) Your mutation is sex-linked.

2) If a female carries an affected W or an affected Z, it is a B female.

3) A male is a B male if it is homozygous for the mutation on Z.

4) Mutation on Z should not be allele to that on W (otherwise it is not sex-linked), so you may have two mutation, one on Z, another on W for B trait.

 

Just my personal opinion...

Edited June 16, 2010 by dttom

[Physicsfan]

N2 would have either ZZ or ZZ'.

normal female can have can have only one genotype ZW

 

ZZxZW would not give a B female at all in any of the 4 possible outcomes.

ZZ'xZW would give only one B female out of 4 outcomes.

[dttom]

N2 would have either ZZ or ZZ'.

normal female can have can have only one genotype ZW

 

ZZxZW would not give a B female at all in any of the 4 possible outcomes.

ZZ'xZW would give only one B female out of 4 outcomes.

 

No, because N2 is derived from B female, so it could only be Z'Z (received affected Z from B female).

So if you breed it with ZW, amongst the female you should get half of them as Z'W.

[Physicsfan]

No, because N2 is derived from B female, so it could only be Z'Z (received affected Z from B female).

So if you breed it with ZW, amongst the female you should get half of them as Z'W.

what if the B female was a ZW'?

[dttom]

Females must have their W from her mother, as her mother is of wild type, there is not such possibility assuming there is no mutation.