Page 2 of 9 < 1 2 3 4 5 6 7 8 9 >
Topic Options
#109886 - 06/17/13 08:37 PM Re: Definitions(genetic load and others) [Re: KazJaps]
KazJaps Offline
Classroom Professor

Registered: 08/30/02
Posts: 2805
Loc: Australia
The Coop: Regaining Brown Egg Colour
R. Okimoto:
Quote:
Chickens have a very high genetic load. It is around 6. Humans have a genetic load of around 2.5. Genetic load is just a rough estimate of the number of recessive lethal and detrimental genes that each animal carries on average. Some carry more and some carry less. Each bird carries a different set. Around 17 out of 20 chicken lines started by single pair matings fail to produce a male and a female by the third or fourth generation of full-sib matings and the line dies out. The lines that eventually make it aren't that healthy either and often have hatchabilities of around 30%.

Top
#109887 - 06/17/13 09:07 PM Re: Definitions(genetic load and others) [Re: KazJaps]
KazJaps Offline
Classroom Professor

Registered: 08/30/02
Posts: 2805
Loc: Australia
Wieslaw, here is the link to that post:

The Coop: Carefoot on Breeding Brother x Sister 20 generations

In the next post on Rokimoto's Inbreeding Depression projects, the following link (using archive.org) will bring it up (on the old board):

Old Board: Rokimoto... please tell us about the breeding projects you have...

eg..
Quote:
I have an Inbreeding depression project where we have backcrossed daughters to sires from a random bred population. We started with 10 sires, but produced enough daughters for the experimental design for only 7. All sires had hatchablities of less than 60% by the second backcross (F=0.375). Most of them less than 30% with two sires at around 11% hatchability. This isn't very good data for most of you trying to breed small populations and maintain production traits.



Quote:
Outcrosses are less likely to produce the homozygous recessive detrimentals and 1/4 of the inbred progeny of any sire would be expected to be recessive homozygotes for any detrimental allele that he carried. Any one chicken carries a lot of recessive detrimentals. Each human carries an average of 5.


So I wonder if that means that chickens carry an average of 12 recessive detrimentals?

--------------------
He also mentions an inbreeding depression project on Quails elsewhere. These were even worse than the chickens.

Top
#109888 - 06/17/13 09:46 PM Re: Definitions(genetic load and others) [Re: KazJaps]
KazJaps Offline
Classroom Professor

Registered: 08/30/02
Posts: 2805
Loc: Australia
R. Okimoto:

Quote:
Overdominance is when the heterozygote Aa is superior to the homozygotes aa or AA. This seems to be relatively rare.

An example of overdominance in chickens is Rosecomb, where R/r+ heterozygote males have higher fertility rates than R/R males (but no difference in females).
-----------------------
Another influence on fitness are co-dominants (not incomplete dominants in this context, not intermediate expression but expression of both alleles, ie different meaning). Eg, MHC/blood groups where there are multiple loci and many alleles. Researchers have found that specific het. combinations have greater resistance to specific pathogens (& diseases), but this specific combination may lower resistance to other pathogens (eg good Marek's resistance but low respiratory disease resistance, etc). In this example, a population has a greater chance of survival if many alleles are within the population (population resistance to multiple pathogens).

Top
#109889 - 06/18/13 12:52 AM Re: Definitions(genetic load and others) [Re: KazJaps]
Henk69 Offline
Moderator
Classroom Professor

Registered: 02/13/06
Posts: 3208
Loc: Netherlands
Why would a R/r+ be superior to a r+/r+? wink
I think that the heterozygote must be superior to both purebreed alternatives to be called over-dominance.

Sickle cell anemia is an example (in malarial regions).


Edited by Henk69 (06/18/13 12:59 AM)

Top
#109897 - 06/18/13 06:48 AM Re: Definitions(genetic load and others) [Re: Henk69]
KazJaps Offline
Classroom Professor

Registered: 08/30/02
Posts: 2805
Loc: Australia
Operational overdominance...

Thomas W. Fox, Roy D. Crawford and J. Robert Smyth (1964).
Rose comb: an example of operational over-dominance in the domestic fowl.

Genetical Research, 5, pp 379-383. doi:10.1017/S0016672300034820.
Abstract

Quote:
The pleiotropic effect of the rose-comb gene (R) on fertility when combined with artificial selection against the single-comb type (r) results in an interesting example of operational over-dominance. An evaluation of the equilibrium frequency of the rose-comb gene based on this over-dominance concept provides a plausible explanation for the relatively high frequency of single-comb birds appearing in the Wyandotte breed of fowls.

Mentioned it too because of Canuck_Bock_RAT's example: Rosecomb (especially with P) less problems with frostbite than with r+/r+.

Similar to Sickle Cell Anemia - genetic benefits depends on environment of individual (SCA het. HgbS no benefit if not in malarial regions).
SCA genetics is also another example of co-dominance, ie hets. express both alleles (not intermediate).
-----------------------------

In the following paper they indicate that there may be some selection going on to keep heterozygosity of MHC alleles:

Cryptic preference for MHC-dissimilar females in male red junglefowl, Gallus gallus.
Mark A.F Gillingham, David S Richardson, Hanne Løvlie, Anna Moynihan, Kirsty Worley and Tom Pizzari.
Proc. R. Soc. B 22 March 2009 vol. 276 no. 1659 1083-1092
Full Paper
Quote:
An increasing number of studies test the idea that females increase offspring fitness by biasing fertilization in favour of genetically compatible partners; however, few have investigated or controlled for corresponding preferences in males. Here, we experimentally test whether male red junglefowl, Gallus gallus, prefer genetically compatible females, measured by similarity at the major histocompatibility complex (MHC), a key gene complex in vertebrate immune function. Theory predicts that because some degree of MHC heterozygosity favours viability, individuals should prefer partners that carry MHC alleles different from their own.....


They also mention the following on comb size selection ...
Quote:
Previous work has demonstrated male mating preferences in the fowl. First, male feral fowl, G. g. domesticus, are more likely to mate with a female with a larger comb (Cornwallis & Birkhead 2007), a trait phenotypically (Pizzari et al. 2003; Cornwallis & Birkhead 2007) and genetically (Wright et al. 2007) correlated with female reproductive investment.

Top
#109905 - 06/19/13 02:29 AM Re: Definitions(genetic load and others) [Re: KazJaps]
Wieslaw Online   content
Moderator
Classroom Professor

Registered: 09/18/09
Posts: 3769
Loc: Denmark
Kazjaps, thanks a lot.

Quote:
First, male feral fowl, G. g. domesticus, are more likely to mate with a female with a larger comb (Cornwallis & Birkhead 2007), a trait phenotypically (Pizzari et al. 2003; Cornwallis & Birkhead 2007) and genetically (Wright et al. 2007) correlated with female reproductive investment.


I challenge this, can't confirm it at all. Au contraire. With me, whenever there are problems with a female not being mated, it is always one with a VERY big comb. The small combed ones have no problems with being omitted.

I also challenge the "recently in fashion" studies "birds of a feather flock together", where allegedly the same coloured birds as by magic keep together. I keep some pens always mixed together from the start. The only exception is that the hens e+ are popular with cocks. Have not observed them being beaten yet. There are always some other more important mechanisms not taken into consideration in all those "studies".





Top
#110004 - 07/02/13 05:57 AM Re: Definitions(genetic load and others) [Re: KazJaps]
Wieslaw Online   content
Moderator
Classroom Professor

Registered: 09/18/09
Posts: 3769
Loc: Denmark
Hi guys, I need some clarification/(pinpointing?) on the use of language concerning combs.

As I understand, there is no single gene for the single comb, and it can be modified by many genes throughout the whole genom(chromosomes 1, 7 and God knows how many more).

1)the term epistatic refers to genes, but on many sites it says " comb X is epistatic to the single comb". Is this usage corect at all?

2) Can the term epistatic be applied at all to the pea comb gene(or rose)? Epistatic to exactly what ?

3) when the pea comb gene combined with rose comb gene makes something "third"((walnut), what is the term for their "relationship" to each other(ie. between the pea and the rose)

4)In one of the (very) old threads, I believe it was Henk? who wrote that D^v was supposed to overwrite? the other mutations(unless I distorted it). Comments on that ? What happens when you add D^v or D^c to the walnut (or rose or pea)?


Thanks in advance .

PS. Henk was very fast to reply, while I was changing the order of the questions



Edited by Wieslaw (07/03/13 04:07 AM)
Edit Reason: added PS

Top
#110005 - 07/02/13 06:40 AM Re: Definitions(genetic load and others) [Re: Wieslaw]
Henk69 Offline
Moderator
Classroom Professor

Registered: 02/13/06
Posts: 3208
Loc: Netherlands
ad 1) No it is not correct, because single comb is the wildtype and thus Always the alternative to the mutation.

ad 2) This is also an "epistatic" effect, I would look for a word starting with syn~ wink

ad 3) Pure D^v/D^v causes a comb flesh reduction making all underlying combtypes hardly visible.

ad 4) See 2, but as we use it (covers/covered by), it would only be hypostatic to Breda and pure D^v

Top
#110006 - 07/02/13 07:55 PM Re: Definitions(genetic load and others) [Re: Henk69]
KazJaps Offline
Classroom Professor

Registered: 08/30/02
Posts: 2805
Loc: Australia
It depends on the context, & whether talking about specific genes or phenotypes.

The problem with 1) statement is not defining 'single-comb' usage, eg whether in reference to a specific genotype or just a phenotype. As Henk mentioned, it is incorrect to use 'epistatis' in reference to the wild-type allele (same locus), eg P peacomb epistatic to p+ single-comb (this incorrect). But you could say P is epistatic to r+, which could be crudely translated as Peacomb epistatic to single-comb (r+) - there lies the problem. It's the same as saying recessive white is epistatic to black, but not defining 'black'.

From an old post...
The Coop: Which is dominant , straight comb or pea comb?
Quote:
“single comb is recessive to all other comb types except....Breda.“

Different loci, recessives, so a good example of “Epistasis”, ie where one gene interferes with the expression of another ( epistasis ).

For example, d/d,r/r,p/p,bd/bd is genetically combless, suppressing single comb. A d/d,r/r,P/P,bd/bd bird is still combless, but suppressing pea comb, & so on.... That is, the Breda combless gene (bd), when homozygous, suppresses all other comb types, regardless of d, r & p loci. Similar to recessive white gene (c/c) suppressing all colour in plumage, regardless of all colour/pattern genes present.

* In Hutt, Genetics of the Fowl:
-“Strictly speaking, pea & rose are not dominant to single comb but epistatic to it. Single comb is “Hypostatic” to these two but epistatic to the combless type of the Breda (Hutt, p88)”

-“ In Breda males, two small papillae on each side of the median line back from the upper beak indicate the duplex condition, although the birds appear practically combless (p87)”

In Crawford, p194: Dv allele is dominant to the Dc allele. The wide cavernous nostrils are expressed with homozygosity for Dv allele but not Dv/d+. Also expressed with Dv/Dc, but only in association with Dv allele.

The Breda breed has the wide-open nostril trait.

------------------------
The P gene: pea comb & breast ridge/reduced feather characteristics is a good example of “Pleiotropy” ie the effect of a single gene on more than one characteristic

* Dv comb & nostril traits also pleiotropism.

Top
#110054 - 07/10/13 02:05 AM Re: Definitions(genetic load and others) [Re: KazJaps]
Wieslaw Online   content
Moderator
Classroom Professor

Registered: 09/18/09
Posts: 3769
Loc: Denmark
Is Polverara rooster's comb "pure" D^v or is something else present in there:



His nostrils look different to my rooster's nostrils


It was presented here:
http://orycteseng.blogspot.dk/2011/01/poultry-polverara-hen-ancient-glory-of.html




Edited by Wieslaw (07/10/13 03:15 AM)

Top
Page 2 of 9 < 1 2 3 4 5 6 7 8 9 >


Moderator:  Admin @ The Coop, Henk69