| 
| 
|
|---|---|---|
Present were 17:
Magda
John Yates
Chuck
Evlyn
Rick
KB Barrett
Lois
Susan
Andy
Emily
Gail
Jason
Dave
Matt
Kenn
Hallie
James
Magda_in_Miami
Hi all, are we doing genetics here today? Hi, I'm glad you can "hear" me. I'm not real used to this site.
Am I supposed to be answering genetics questions today? If so, Is everyone clear about dominant and recessive traits and homozygosity/heterozygosity?
marylois
Maybe a teeny little review?
Magda_in_Miami
Recessive trait is one that has to be inherited from both parents to be manifested. Dominant traits need to be inherited from just one parent to show up. Dominant is called this because it masks the effects of the recessive trait. A dominant/dominant and dominant/recessive genotype (what's in your genes) look the same - they both have a dominant phenotype (what you observe). Only the recessive/recessive genotype will give you the recessive phenotype, so that is the only time you can know for sure that your plant is homozygous (for that particular gene) by just looking at it. Is this pretty clear so far?
Prankster__Susan
I'm with ya, Magda.
Magda_in_Miami
To be homozygous for a trait (gene) means that you have the same form from both parents. To be heterozygous means that you got a different copy from each parent. This is important in breeding because only plants homozygous for a particular trait will breed true for that trait.
KB_Barrett
So, if brown eyes were dominant over blue eyes, any amount of brown genes would 'mask' the blue genes. A person would have to have only blue genes to have blue eyes, brown and blue would show up as brown.
Magda_in_Miami
Then there is co-dominance, which means that both genes are partially expressed, neither is dominant to the other.
Brown eyes and blue eyes is an example of dominant/recessive inheritance. Genotype brown/brown and brown/blue both have the phenotype "brown". Genotype blue/blue has the phenotype "blue". Co-dominance would be like skin color - the kids usually come out somewhere in between the parents.
Some characteristics are a result of multiple genes and then the inheritance looks more like co-dominant that the dominant-recessive model. Sometimes it can be hard to tell how a trait is inherited without doing many generations of breeding.
[This message and the three following it are independent of the rest of the talk - mp]
Coerulea
I am researching the inheritance of the Coerulea color form in Cattleya and Laelia species.
Prankster__Susan
How do you do that, Coerulea, by making test crosses?
Coerulea
I really just started, my first crosses are coming out of the flasks now, I am really still learning about previous research that has been done.
Magda_in_Miami
The inheritance I've spoken about so far is called "nuclear inheritance" because it involves the genes that are located in the nucleus of the cell. These genes are inherited equally from each parent.
The other kind of inheritance is cytoplasmic inheritance. This involves the genes in the mitochondria and chloroplasts. These genes are inherited only from the pod parent. Does everyone know what mitochondria and chloroplasts are?
marylois
Not I.
Magda_in_Miami
Mitochondria are the parts of the cell (called organelles [or sometimes plastids]) where respiration takes place. (Animals have them, too.) They have their own DNA and are actually believed to have arisen from a symbiosis between the large cell and a little bacteria-like creature.
Chloroplasts are the organelles where photosynthesis takes place and they are obviously present only in plants. They are also believed to be the result of an ancient symbiosis. Of course now, it's no longer a symbiosis because neither can survive independently.
The organelles (mitochondria and chloroplasts) as well as just about the whole cytoplasm of the cell, are inherited from the pod or female parent. The only thing the pollen parent contributes is its nuclear DNA.
Rick54
And each of them - chloroplast and mitochondria have their own DNA? Amazing...
Magda_in_Miami
Yes, chloroplasts and mitochondria have their own DNA and they even have a genetic code that is slightly different fron the nuclear DNA.
Rick54
Hence the greater influence of the pod parent!
marylois
Certainly explains why Marilyn and others have been attributing some traits specifically to the female parent.
Rick54
Own DNA - intelligent everything with properties of its own and options for each own function at each level - makes sense!
EquitantMan
Well, I've got more to think about the next time I make a cross that's for sure!
Magda_in_Miami
Right. In the end, the pod parent contributes more genes. It's only important for some traits but when it counts, you got to know about it!
Hallie,_VA,_USA
Are there specific traits (substance/texture, for example) more associated with the pod parent, or is it more varied than that?
Rick54
This means that for all but the nuclear traits, find the right traits in the pod parent.
Magda_in_Miami
The effect of one or the other parent is probably not due to the cytoplasmic inheritance alone. There is also something called imprinting. This is when the gene coming from one of the parents is inactivated before the zygote is formed. Then only the gene from the other parent has an effect. (Actually, I don't know for sure that imprinting happens in plants but it's well-established in animals, so I don't see why not.)
[Actually, *most* of the time you see a lot of traits seemingly inherited from one parent only, it's probably because that parent has the dominant genes. Cytoplasmic inheritance and imprinting need to be kept in mind but I don't want everyone to get the impression that they are the most important form of inheritance.]
Chuck,AustinMN
I can see how chloroplast and other plastid genes are of interest to breeders since they may influence color, but are mitochondrial genes of great importance to a plant breeder??
55SS
Isn't it that there are dominant and recessive genes for each trait, but with certain traits, co-dominance is possible?
Magda_in_Miami
Bear in mind that the vast majority of traits are coded for by nuclear genes. Only a handful are cytoplasmic. Most of the time we don't care what the plant's photosynthetic enzymes are like. But in some flowers the chloroplasts contribute to color and that's when you have to use the pod parent with the right chloroplasts.
Magda_in_Miami
No, I don't know of any mitochondrial genes that are important in breeding.
Rick54
Imprinting, isn't that just a type of learning? How would there be imprinting in plants? (We can talk about this later if it is too tangential)
Magda_in_Miami
55SS - co-dominance is found in certain traits and in others the recessive/dominant system works. You just have to know how each trait is inherited.
Magda_in_Miami
Genomic imprinting is not the same thing that happens to baby birds right after they are born. It's thought to be a chemical "stamp" put on the gene during meiosis (the cell division that leads to formation of reproductive cells).
Rick54
Ok.
Magda_in_Miami
Someone was asking about which traits are inherited with organelles. The ones important in breeding are color in some green and yellow flowers. Substance and texture are probably polygenic - the result of many genes acting together.
James_in_Fresno
Is the genomic imprinting the actual division of the cell during meiosis where half of the chromosomes go to one cell and the other half to the other? As far as a cell getting which particular chromosomes?
Magda_in_Miami
No, the splitting of the chromosomes is called the reduction division. A copy of an imprinted gene still goes to each daughter cell but the gene itself is inactivated. A gene could be inactivated in either the pod or
the pollen parent. It all depends on the gene. This is pretty complicated and I don't think it's something you need to understand in detail, just something to keep in the back of your mind if you are seing "weird"
things happening in crosses.
James_in_Fresno
I have a seedling out of flask since last Saturday. It is a clone, but one of the seedlings has a funnel shaped leaf instead of a normal leaf. This happens to be the only example in this particular flask. Would that be like one of the 'weird' things?
Magda_in_Miami
Funnel-shaped leaf - I guess it could be, but I'd give the plant some time to see whether all the leaves come out like that or whether that one just had something happen to it.
James_in_Fresno
This was the only leaf. There is another leaf coming out of the center that appears to be normal so far.
Magda_in_Miami
Then I would say that it was just environmental - that's a lot more likely that a genetic cause in this case.
James_in_Fresno
Ok.
Magda_in_Miami
Things seem pretty slow. Is everyone pooped out? Shall we call it a night. Speak up now if you have questions!
James_in_Fresno
Was the discussion about Paph genetics? Green and Yellows? Are greens and yellows dominant in Paphs?
Magda_in_Miami
Just genetics in general. Paphs are the ones where the yellow color is inherited from the pod parent only, because the gene is in chroloplasts.
James_in_Fresno
Ok. Is white coloring the same?
Magda_in_Miami
Yellow in some paphs is not dominant in the usual way. It's just inherited exclusively from the pod parent. The pollen parent does not contribute anything
at all in this case.
James_in_Fresno
Does that mean that the bloom will tend to be yellow, or do the other colors involved in the cross come through?
Magda_in_Miami
Inheritance of white is usually recessive - it's an absence of color. However, in cattleyas you see unexpected effects because there are several genes acting in concert to make the flower white.
Magda_in_Miami
In the paph case, the flower will be whatever color has been inherited via the nuclear genes with a yellow overlay if the pod parent is yellow. So if you have a purple pollen parent and a yellow pod parent, you would expect at least some of the flowers to be purple with a yellow overlay. If your pollen parent is heterozygous for white/purple, then you will see some yellow progeny (white with yellow overlay).
James_in_Fresno
Ok. I have an interest in white or orange/peach colored paphs and was wondering how the colors were inherited.
Magda_in_Miami
James, just make sure your pod parent is the color you want. For the light colors that should be the greatest effect.
James_in_Fresno
Well, it's 11:00PM where you are, and I am getting tired as well. Thank you for the information on the Paphs. Goodnight.
Magda_in_Miami
You are welcome. And I think it's time for me to go, too.
marylois
Magda - thank you!
Evlyn
Thanks for the chat Magda. do appreciate your taking the time to talk with us
Rick54
Thanks Magda, Great information! 'nite all. *poof*
|
|
|
|
|---|---|---|