Dark and Blue linkage rate in IRN

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Recio
Posts: 966
Joined: Thu Mar 26, 2009 2:09 am
Location: France

Dark and Blue linkage rate in IRN

Post by Recio »

Hi everybody,

It is commonly accepted that the gene location (loci) in the chromossomes is roughly conserved among species, specially inside the same familly (parrots for us), so that results obtained in one species can be extrapolated to others.
Budgie is the parrot species with a higher reproduction rate, higher number of identified mutations and longer breeding history and, thus, most of results about gene location and linkage rates come from budgi studies. We are currently accepting such results as the theoretic frame of our breeding planing, without further questioning.

Here I want to analyze what we really know:

About budgies: http://en.wikipedia.org/wiki/Dark_budgerigar_mutation

"The loci of the Dark mutation and the Blue allelic series are situated on the same autosome, so the Dark mutation is linked to the Blue allelic series. The cross-over value (COV) or recombination frequency between the Dark and Blue loci is often stated to be about 14%, but several careful measurements of this COV show quite widely varying results. Early measurements by Duncker and independently by Steiner obtained values of 14% and 7.6% respectively, and T G Taylor and C Warner collected results which showed only 5 cross-overs in 140 - a COV of 3.6% . Included in these were results from T G Taylor's own experiments, in which he found no cross-overs in 86 birds bred. It is now known that the environment and other genes can influence the COV, so some variability should be expected. A reasonable average of these measurements is a COV of 8%."

Some questions:

1. Why should we accept a COV of 14% for IRN if the detected values in budgies show such a wide range (0-14%)?
2. Is it logical to accept that the COV in one species can change depending on the presence of other mutations or on environemental factors, and at the same time to accept that the COV is "fixed" among species?
3. Do we have any prove that the known IRN blue locus and the Budgie blue locus are one and the same? The behaviour of homozygous parblues in both species is different and, thus, we should think that we are facing different blue loci ... showing different linkage rates with Dark.

The best experiment to prove or disprove that both Blue mutations in IRN and Budgies are/not the same would be to hybridaze a Blue IRN x Blue Budgie.... but it is not possible. Do you know any psittacula species able to hybridaze with IRN, and showing an homozygous parblue bluer than the heterozygous ParblueBlue (like Budgies)?

Has anybody breeding cobalts and Dark greens found some "strange" offspring results?

Regards

Recio
Indian Ringneck Vic
Posts: 91
Joined: Thu Aug 23, 2012 8:24 pm

Re: Dark and Blue linkage rate in IRN

Post by Indian Ringneck Vic »

Hi Recio as you are one that thinks outside of the box I thought I might propose a challenge that only a crank such as myself would suggest and pre warn of hysteria that my statement will cause. I am of the opinion that the punnet box theory of Mendel is flawed and should not be used as it is out dated and way to simplistic to be applied to birds.Now lets see what our budding experts have to say about that heretic statement.If this statment is correct it throws all their percentages out the window .
Recio
Posts: 966
Joined: Thu Mar 26, 2009 2:09 am
Location: France

Re: Dark and Blue linkage rate in IRN

Post by Recio »

Hi Paul,

The punnet box is a statistic tool to study qualitative variables. We can use it to study Mendel laws, but we should keep in mind other factors which can disturb the results (presence of linkage, master genes, intergene dependency expression, masking, ...). When experiment results do not match expected values in the Punnet box it does not mean that the statistical method is not correct but that such confusing factors are present, and we should again use advanced statistics to unmask them. The Punnet box is really the very first step analyse and sometimes, as you say, it is not enough.

Regards

Recio
Johan S
Posts: 1215
Joined: Wed Mar 30, 2011 1:24 am
Location: Pretoria, South Africa

Re: Dark and Blue linkage rate in IRN

Post by Johan S »

Hi Recio, from what I've seen and heard in IRN, the crossover of dark and blue is rather difficult and therefore the region of 15% sounds reasonable to me. I don't know if anybody has crunched the numbers though. The white eye ring group of lovebirds also has a dark and blue factor. Unfortunately, at the time when I bred with them, I was much to young and didn't pay attention to such thing. And I suspect we started with cobalts, so the (de)crossing over was missed by myself at the time. Might be worth pursuing some data for those species too.
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