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#101 2012-03-10 18:51:42

ipf
Member
From: Salt Spring Island, BC, Canada
Registered: 2011-08-29
Posts: 168

Re: Topic 2: Genetics Terms and Definitions

too bad. . .

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2012-03-10 18:51:42

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#102 2012-03-11 19:12:27

ipf
Member
From: Salt Spring Island, BC, Canada
Registered: 2011-08-29
Posts: 168

Re: Topic 2: Genetics Terms and Definitions

Batch 6:
Original versions (I’m lumping together the terms “inhibiting gene” and “epistasis”)
Inhibiting gene - a gene that prevents the expression of another gene. See also epistasis.
Mosby's Medical Dictionary, 8th edition. © 2009, Elsevier.

Epistasis. An interaction between genes at different loci in which one gene masks or suppresses the expression of the other.

The masking of the phenotypic effect of alleles at one gene by alleles of another gene. A gene is said to be epistatic when its presence suppresses the effect of a gene at another locus. Epistatic genes are sometimes called inhibiting genes because of their effect on other genes which are described as hypostatic.

Epistasis can be contrasted with dominance, which is an interaction between alleles at the same gene locus. http://en.wikipedia.org/wiki/Epistasis

Discussion: Wikipedia is generally spot-on, IMO, with its definitions. However, this is one of those no-so-good ones. Epistasis can refer to any situation where the expression of the affected locus is modified – it could be suppressed, enhanced, or just different.

I would suggest:
Epistasis. An interaction between genes at different loci in which an allele at one locus modifies the expression of alleles at one or more other loci.

Original version:
Inbreeding - The act of mating closely related individuals.
Discussion: The trouble with this one is that all individuals are related somewhere along the line, if you go back far enough – e.g. you’re related to your chooks. People have tried to get around this by referring back to the average inbreeding level in a given population and then calling a given mating “inbreeding” only if it is more so than the average. But when you think of animals like cheetahs – any mating between two cheetahs is inbreeding, IMO, as they’re all so closely related. So we have to step back and focus on concept rather than precision.

Also, while inbreeding results from the mating of two related individuals, it is applied to the progeny, not so much to the act itself. . .

I would suggest:
Inbreeding - The result of mating (closely) related individuals. An individual is said to be inbred if its parents were (closely) related. Can be quantified using the inbreeding coefficient (=F; also called COI). There are many different crosses and breeding strategies that involve inbreeding and are used in animal and plant breeding programs. These include back-crosses, sib matings and line-breeding. Note that the progeny of two highly inbred individuals who are not related to each other will (perhaps surprisingly) have F=0; they are not inbred.

Original version:
Line breeding - Selective inbreeding to perpetuate certain desired qualities or characteristics in a strain of livestock.
Article on line breeding and inbreeding: http://bowlingsite.mcf.com/genetics/inbreeding.html

I would suggest:
Line breeding – Selective inbreeding to perpetuate certain desired qualities or characteristics in a strain of livestock. The term “line breeding” commonly carries a positive connotation, suggesting care and deliberate effort, while "inbreeding" is generally viewed negatively.

Last edited by ipf (2012-03-11 19:13:33)

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#103 2012-03-11 20:07:03

Maggiesdad
Moderator
From: Louisa County, Virginia
Registered: 2011-10-05
Posts: 1980

Re: Topic 2: Genetics Terms and Definitions

ipf wrote:

too bad. . .

Don't imagine that your work is going unappreciated, ipf! I find myself reading your  suggestions versus our definitions over and over, making sure I comprehend the subtle nuances of the changes you have proposed. I'm amazed at how a word here or there or a tweak to this or that phrase can impact the meaning of these definitions.

Once again, thank you so much for your input.
:thanks: Glen

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#104 2012-04-13 02:28:42

poplar girl
Administrator
From: Athabasca, AB, Canada
Registered: 2011-06-30
Posts: 3159

Re: Topic 2: Genetics Terms and Definitions

I do believe we have the following terms left to discuss:
Recombination
Sex linked
Spiral breeding

ipf are you up for finishing our definitions =D


Raising red cuckoo (marraduna) Euskal Oiloak and self blue (lavender) & black Belgian Bearded d'Uccles.

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#105 2012-04-13 09:34:05

gubi
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From: Walton
Registered: 2011-06-30
Posts: 1344
Website

Re: Topic 2: Genetics Terms and Definitions

When we do sex linked we should do a list of traits that are sex linked with the EO's.


Herd of Brown Swiss, a few sheep, red cuckoo basque, Silverspangled Appenzeller Spitzhauben, ameraucanas(EE), Welsummer, broodie silkies and a few more heritage hens

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#106 2012-04-13 12:21:05

poplar girl
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From: Athabasca, AB, Canada
Registered: 2011-06-30
Posts: 3159

Re: Topic 2: Genetics Terms and Definitions

We can and there are quite a few, i am surprized by how many. I wonder if some are linked as well.

if you look at topic 3 I think most are listed there. I will sticky that list of traits when discussion wraps up.


Raising red cuckoo (marraduna) Euskal Oiloak and self blue (lavender) & black Belgian Bearded d'Uccles.

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#107 2012-04-13 14:20:06

ChestnutRidge
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From: Western Virginia
Registered: 2011-07-05
Posts: 251
Website

Re: Topic 2: Genetics Terms and Definitions

So, barring ("B") is sex-linked and dominant.  A rooster has two alleles for the gene and can be heterozygous (B/b) or homozygous (B/B, or b/b).  He passes one of his two genes to all of his offspring.  A hen has one allele which she passes down only to her sons. 

Male B/B + Female B = 100% B females; 100% B/B males (100% barred phenotype)
Male B/B + Female b = 100% B females; 100% B/b males (100% barred phenotype)
Male B/b + Female B = 50% B females, 50% b females; 50% B/B males, 50% B/b males (75% barred phenotype)
Male B/b + Female b = 50% B females, 50% b females; 50% B/b males, 50% b/b males (50% barred phenotype)
Male b/b + Female B = 100% b females; 100% B/b males (50% barred phenotype - only males are barred, so "sex-link")
Male b/b + Female b = 100% b females; 100% b males (0% barred phenotype)

Did I do that right?

I know that lack of dermal melanin is supposed to be sex-linked, but I'm not clear on that one.  The presence of barring also inhibits the expression of dermal melanin, so that one is pretty complicated... Someone else can try their hand at that.

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#108 2012-04-14 02:05:07

ipf
Member
From: Salt Spring Island, BC, Canada
Registered: 2011-08-29
Posts: 168

Re: Topic 2: Genetics Terms and Definitions

sorry. .. life has been a bit hectic. Will get back on the ball in the next couple of days.

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#109 2012-04-14 16:15:39

ipf
Member
From: Salt Spring Island, BC, Canada
Registered: 2011-08-29
Posts: 168

Re: Topic 2: Genetics Terms and Definitions

Batch 7 (plus mitosis and meiosis)
Original version:
Recombination - The occurrence of progeny having combinations of traits different from the combinations seen in the parents (due to crossing-over and independent segregation of chromosomes). (Reference) In recombination, cross-overs exchange alleles between homologous chromosomes during meiosis in both parents. This is what allows for much of the genetic variation in the offspring of a population in each generation. (Answers.com, Overly technical article, Second overly technical article)

Discussion:
Recombination refers really just to crossing over during meiosis (formation of gametes), not independent segregation.
Even without crossing over, there’d still be lots of variation – what we wouldn’t get is the breaking up of linkage. For example, the allele for pea comb would ALWAYS go with the allele for blue eggs, instead of just 95% of the time!

I would suggest:
Recombination is the result of crossing over of homologous chromosomes during meiosis (which results in eggs and sperm). During this process, the paired chromosomes (one from each parent) line up together and exchange bits. This results in the separation of linked alleles. For example, the blue egg locus (O;o) is tightly linked to the Pea comb locus (P;p). If an individual inherited OP from one parent, and op from the other, its genotype (for these loci) would be OP/op. Without crossing over, it would only generate two types of gametes, OP and op. With crossing over (and thus recombination) it can generate Op and oP gametes as well, which is why you sometimes get a bird with a straight comb laying blue eggs; it got the Op allele form its half-Ameraucana parent and an op (or possibly Op) allele from its other parent.
This process allows for a huge increase in the amount of diversity in a population. Interestingly, Mendel didn’t figure this out; he thought all loci assorted independently.

Original version:
Meiosis - The process of two consecutive cell divisions that produces haploid sex cells and spores from diploid progenitor cells. Meiosis results in four daughter cells, each with a haploid set of unreplicated chromosomes.
Cell division of the sex cells. Haploid cells containing one half the regular number of chromosomes are formed through this process. These are called gametes with the male producing sperm and the female egg cells. Each haploid gamete (i.e. sperm or egg cell) can carry a unique combination of genetic material as a result of recombination that occurs during cell division. Thus a single egg cell will have some DNA from the female's mother and some from the father. The sperm will have some genetic material from both of the father's parents. The two gametes (sperm and egg) then join (fertilization) and form a zygote with a unique combination of traits.

Comment: This is good. Might just add a bit about eggs and sperm, and delete bits that don’t apply to animals (e.g. spores), and condense it a bit.

I would suggest:
Meiosis - The process of two consecutive cell divisions that produces haploid sex cells from diploid progenitor cells. Meiosis results in four “daughter” cells, each with a haploid set of unduplicated chromosomes. These haploid sex cells, or gametes, are the eggs and sperm in animal species. Each gamete carries just one of the two alleles at each locus in the parent’s chromosomes, and each gamete is genetically distinct (unique).

Original version:
Mitosis - the division of the chromosomes of the cell to form two identical sets. Mitosis is generally followed by cytokinesis which is the division of the rest of the cell. Together these are called the mitotic phase. The two new cells formed will be identical to the parent cell unless errors are made during cell replication.

I would suggest:
Mitosis – strictly speaking, mitosis refers to the division of the chromosomes of the cell to form two identical sets, but in common usage mitosis generally refers to the entire mitotic phase, which includes cytokinesis (the division of the rest of the cell). The two new cells formed will be identical to the parent cell unless errors are made during cell replication.

Original version:
Sex linkage - A linkage involving a locus on the X or Z chromosome. In certain crosses sex-linked traits manifest themselves only in the heterogametic sex. (Reference) In many organisms, sex of the individual is determined genetically by the presence or absence of particular sex-chromosomes. For example: in humans, XX is female, XY is male; in chickens, ZW is female, ZZ is male (ie the male is homogametic not the female). (Reference)
Everything you want to know about sex-linkage on this BYC forum thread

I would suggest
Sex linkage - A sex-linked trait is one controlled by a locus on the Z (or W) chromosome in birds (X or Y in mammals). Since the W chromosome carries few loci, most sex-linked loci are on the Z chromosome. In certain crosses sex-linked traits manifest themselves only in the heterogametic sex, which is very useful, as it allows sexing of new hatchlings. This requires that the male parent be homozygous for the recessive allele and the female to have (a single copy of) the dominant allele.
An example of a sex-liked gene is B, for barring. Crossing a barred female (B/-) with a non-barred male (b/b) will give all barred (but heterozygous) male offspring (B/b) and all unbarred (b/-) female offspring. 

As I'm a geneticisit, not a breeder, I won't attempt "spiral breeding". I'm not a big believer in recipes for breeding; to me breeding is simply about keeping inbreeding as low as possible and getting rid of deleterious alleles, while making progress in desired traits.

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#110 2012-04-15 12:28:49

poplar girl
Administrator
From: Athabasca, AB, Canada
Registered: 2011-06-30
Posts: 3159

Re: Topic 2: Genetics Terms and Definitions

ChestnutRidge wrote:

So, barring ("B") is sex-linked and dominant.  A rooster has two alleles for the gene and can be heterozygous (B/b) or homozygous (B/B, or b/b).  He passes one of his two genes to all of his offspring.  A hen has one allele which she passes down only to her sons. 

Male B/B + Female B = 100% B females; 100% B/B males (100% barred phenotype)
Male B/B + Female b = 100% B females; 100% B/b males (100% barred phenotype)
Male B/b + Female B = 50% B females, 50% b females; 50% B/B males, 50% B/b males (75% barred phenotype)
Male B/b + Female b = 50% B females, 50% b females; 50% B/b males, 50% b/b males (50% barred phenotype)
Male b/b + Female B = 100% b females; 100% B/b males (50% barred phenotype - only males are barred, so "sex-link")
Male b/b + Female b = 100% b females; 100% b males (0% barred phenotype)

Did I do that right?

I know that lack of dermal melanin is supposed to be sex-linked, but I'm not clear on that one.  The presence of barring also inhibits the expression of dermal melanin, so that one is pretty complicated... Someone else can try their hand at that.

You did it right Chestnutridge! Nice! Are you sure you don't want to take a shot at drawing this out for dermal melanin? I think you could do it!


Raising red cuckoo (marraduna) Euskal Oiloak and self blue (lavender) & black Belgian Bearded d'Uccles.

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#111 2012-04-15 12:36:39

poplar girl
Administrator
From: Athabasca, AB, Canada
Registered: 2011-06-30
Posts: 3159

Re: Topic 2: Genetics Terms and Definitions

And thanks for the last of our definitions ipf, I think this will be a great reference to come back to. I will add them to the stickied list.


Raising red cuckoo (marraduna) Euskal Oiloak and self blue (lavender) & black Belgian Bearded d'Uccles.

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#112 2012-04-15 13:47:40

ChestnutRidge
Member
From: Western Virginia
Registered: 2011-07-05
Posts: 251
Website

Re: Topic 2: Genetics Terms and Definitions

poplar girl wrote:

You did it right Chestnutridge! Nice! Are you sure you don't want to take a shot at drawing this out for dermal melanin? I think you could do it!

Thanks, PG!  I should probably put the "/-" for the females like you did in the other post.  Is it exactly the same for the dermal melanin, just with some other things, like barring and ????, affecting the expression of those traits?

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#113 2012-04-15 14:11:17

poplar girl
Administrator
From: Athabasca, AB, Canada
Registered: 2011-06-30
Posts: 3159

Re: Topic 2: Genetics Terms and Definitions

Yes, it is exactly the same except that sex linked barring will mask expression of dermal melanin in homozygous barred males. In heterozygous barred males (B/b) but i believe if you have a id/id you can see the green or blue showing through. Id is dominant so I think only males with id/id would show dermal melanin.

We could post these in the sex linked traits thread ipf started if you wanted to Chestnutridge :)


Raising red cuckoo (marraduna) Euskal Oiloak and self blue (lavender) & black Belgian Bearded d'Uccles.

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