Argghhhh :). Bev, you did it. I was trying my darndest to fight the urge
to start making Punnett's squares and going into a discourse on Mendellian
genetics. Well, I guess it had to happen sooner or later. When you start
talking about gene suppression, co-dominance, and partial dominance things
can get a little sticky. Genetics is a fascinating topic though. This
post was very thorough and and an excellent explantion. TC
PS Those superglued eggs are a pain to incubate.
At 04:11 PM 12/20/00 -0500, you wrote:
>> This person implied that the genetics explanations used the term 'look
normal'
>> to refer to the dominant colour in the crosses. Normal, could be the
wild type
>> colours, or whichever was more dominant of the two colours being
crossed. More
>> dominant? Got me thinking.
>
>THe problem is that most simple explanations talk about a single mutation of
>a single gene, so there are only two alleles, the mutant form and the
original
>form, traditionally called 'wild-type'. Like anything in biology, the real
>world is messier. While there can be multiple variant alleles of a single
>gene, there are usually multiple genes controlling traits like skin color
>and pattern in a lizard.
>
>Dominant vs recessive applies only to the alleles of a particular gene.
>There's another concept called epistasis. This means that the effect of
>a mutation in one gene prevents another gene from expressing its phenotype.
>Let's do this in mice, since leo genetics are not that well worked out.
>All albino mice have white fur and red eyes. THey may also have the genes
>for other coat colors and patterns, like piebald, black, etc., but because
>they are unable to produce any dark pigment at all, you have no way of
>knowing what other coat color traits they have, except by breeding
experiments.
>Similarly, white coat color in cats is a simple dominant, epistatic to all
>other coat colors, and unrelated to white spotting. So you can't tell if
>a white cat has genes for white spots unless you do breeding experiments
>(or know a lot about its family tree). You also don't know if it's "really"
>a tabby or black or gray or marmelade, either, but you can tell by breeding
>experiments which alleles of which genes it carries.
>
>> Don't laugh, but .... according to what I'd been told, if you crossed,
as an
>> example, a normal and albino, the hets would look normal, since it's
dominant
>> over albino. No problems there.
>
>Right, but it might be less confusing if they said 'albino' and 'non-albino'.
>
>> But, taking 'recessive' traits like albino and
>> patternless, you'd get hets that look patternless, since according to this
>> source, patternless is dominant over albino. The 'look normal' hets
would in
>> this case be patternless carrying albino genes.
>
>Here's where your 'expert' heads off into left field. As far as I know,
>albino and patternless are alleles of different genes, and they assort
>independently. Assuming there are no patternless geckos in the ancestry
>of the albino, the albino has two 'normal' or 'wild-type' or
'non-patternless'
>alleles for the patternless gene. Ditto, if the patternless animal has no
>albinos in its ancestry, it has two 'normal' or 'wild-type' or 'non-albino'
>alleles for the albino gene. So when you cross them, the offspring each
>get one allele for albino from one parent and one allele for non-albino
>from the other parent. The also get one allele for patternless from one
>parent, and one allele for non-patternless from the other parent. So they
>are heterozygous for each trait, and since both traits are recessive and
>they have a normal allele for each trait, the recessive traits won't show.
>What they actually look like, other than not-albino and not-patternless,
>depends on the rest of their genes.
>
>> What really got me suspicious
>> was the suggestion that 'two equally recessive' traits (whatever that term
>> means), would fight it out. The topper was that in this case, blizzard and
>> albino, both being 'equally recessive', the daughters would be whatever the
>> mother is, the sons take after father, but all would carry the other
parent's
>> genes. Once I heard that, I just knew something wasn't right.
>
>Oh, yeah, in an animal that has its sex determined by the temperature days
>or weeks after fertilization, this is a dead giveaway that the speaker is
>either seriously confused or seriously bullshitting.
>
>> This expert also said that all the normal looking hets I'd seen had to
have been
>> normal X somethings, to have the offspring with normal colours. Albino X
>> patternless would have been patternless coloured hets.
>
>These two traits should behave independently, so if you cross your albino
>x patternless to an albino, you'll get half albino and half non-albino.
>Half of the offspring will also be het for patternless, but you won't know
>which half. DItto if you cross the albino x patternless to a patternless,
>you'll get half patternless and half non-patternless. Half of these
offspring
>will be het for albino, but again, you won't know which. If you cross two
>albino x patternless to each other, you'll get the classic 9:3:3:1 ratio -
>on average 9 of 16 will appear neither albino nor patternless, although
>some will be het for one, the other, or both; 3 will be albino and may be
>het for patternless; 3 will be patternless and may be het for albino; and
>one will be both albino and patternless - you may not be able to distinguish
>this from albino.
>
>It's a lot easier if you use symbols and Punnett squares. Let's use A and a
>for the albino trait and P and p for patternless. A is the non-albino or
>normal or wild-type allele for the albino gene and a is the albino allele.
>Similarly, P is the normal allele for patternless and p is the patternless
>allele. It's a convention to use capital letters for the dominant allele
>and small letters for the recessive allele.
>
>So your albino gecko that has no patternless in its ancestry has the formula
>aaPP, and the patternless that has no albinos in its ancestry is AApp. When
>you cross them, all the offspring are AaPp. They don't show either albinism
>or patternlessness, but they are heterozygous for both traits. These geckos
>can produce gametes (eggs or sperm) of four types: aP AP ap Ap. If you cross
>one to its albino parent, you get:
>
> aP AP ap Ap
>
> aP aaPP AaPP aaPp AaPp
>
>i.e. half are albino (aa) and half are heterozygous for albino (Aa). Half
>of each group is also het for patternless (Pp) and half isn't (PP) but you
>can't tell which without further breeding experiments. The cross back to
>the patternless parent is left as an exercise for the reader.
>
>If you cross two of these AaPp animals, you get:
>
> aP AP ap Ap
>
> aP aaPP AaPP aaPp AaPp
>
> AP AaPP AAPP AaPp AAPp
>
> ap aaPp AaPp aapp Aapp
>
> Ap AaPp AAPp Aapp AApp
>
>
>You can pick out the 9 of 16 possibilities that have both at least one A
>allele and one P allele, these are the 'normal' phenotypes. There are 4
>of 16 that are aa, and these geckos will be albino independent of whether
they
>have one, two or no P genes, because albinism is epistatic to patternlessness
>(ideally). That is, you can't distinguish an albino that is homozygous for
>patternlessness from one that isn't. The remaining 3 of 16 have at least
>one A allele and 2 p alleles, so they will be patternless. 2 of these 3
>are also het for albino.
>
>Btw, if any of you have followed this far and are still confused, get an
>introductory biology text for an explanation by someone who does explanations
>for a living. It's all the same, geckos or peas or fruitflies.
>
>> Live and learn. huh?
>
>Gosh, I hope so! (But we can't always count on it...)
>
>> > That's how you might get a het for
>> > patternless/blazing/avocado/samurai/stapler leopard gecko :)
>>
>>Sounds like you're describing a vibrant green coloured patternless 'hot
female'
>>who glues her eggs to the nesting box.
>
>With superglue!
>
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