Lots of Questions

Hey all,

Well, I’ve finally decided to try my hand at this and was directed to this site. I may break this into separate posts so its not too lengthy.

I have some basic genetics knowledge, but I’m obviously missing something relative to quadrivalent formation. I read the article on Glossy vs. Dull Foliage. The article states that the one parent has a Gggg while the other parent has a gggg. I arrive at 16 possible combinations with a ratio of 25% glossy. The article states an expected ratio of 15:13. What am I missing here? I’m thinking that I’m somehow losing it in the division area. I also don’t understand the statement that “any two of these may be segregated at random to the gametes”.

Can someone please explain this to me or direct me to where I can find a “rose genetics for dummies” explanation.

Thanks.

Melanie

Melanie,

I thought that I might take a crack at your original question, regarding the inheritance of traits in tetraploid roses. Even if the trait really is controlled by only one gene, the article you read has over-simplified the situation. There are extra variables in tetraploid inheritance, and you are sometimes forced to make assumptions with very little information. For example, do the 4 copies of the same chromosome form 1 group of 4 (tetravalent) or 2 groups of 2 (bivalents). The article you mentioned assumes 1 tetravalent, but what little scientific literature I have seen indicates that the actual situation is mixed: Sometimes a tetravalent forms, and sometimes the same rose may make 2 bivalents instead.

Each of these assumptions leads to different numbers, but the situation can be summed up easily enough: Recessive phenotypes are much rarer in tetraploid crosses than in diploid crosses. Probably the most important trait that is recessive (and therefore difficult to regain once lost in a cross) is the ability to bloom recurrently. Once-a-year bloom is dominant.

Hey Roger,

That’s interesting. Thanks for the info.

Let me ask another question. I went out to the garden and took a leaf from each rose. I laid them all out and then classified them for glossy vs dull. What I was trying to do is see if I could tell by the amount of gloss or lack thereof what genes the rose has. I classified the extremely glossy leaves as “GGGG”, the glossy as “GGGg” and the semi-glossy as “GGgg” and “Gggg” respectively on how I perceived the amount of glossiness (I think I just made up a word). The dull leaves I classified as “gggg”. Is this at least fundamentally correct? or am I way off?

Thanks for you help.

Melanie

Melanie,

Unfortunately, inheritance of traits is hardly ever as simple as we’d like it to be. (Then again maybe the complexity is a good thing afterall)

I wouldn’t guess that you could tell the genotype by the degree of glossiness, except maybe that the plant has or doesn’t have at least one G (glossy) gene. I’m guessing that modifier genes are probably more likely to be responsible for just how glossy a particular plant turns out to be. Some modifier genes would make a glossy (G***) plant less glossy; some would make a non-glossy (gggg) plant more glossy than normal. It is possible though, that a “dosage” effect is what is causing the degrees of glossiness you’ve noticed. In this case, you wouldn’t be “way off”, you’d be “right on the money” in your classifications of genotypes.

I guess my point is, don’t let the cloudiness scare you away from trying whatever you’re interested in. Even the generally accepted truths have exceptions. Have fun, Tom

Thanks Tom.

I’m now trying to tackle the magenta hues going along the same premise. Obviously this will be much more complex given there are a multitude of factors involved with color and then depth of color. But, we all have to start somewhere right?

I’m sure I’ll have questions on this as I go further.

Thanks again to everyone for your help.

Melanie

Hey all,

Just an update. I’ve finally figured out how we get to 28 chromosomes. Holy smoke, that was way too much like science (hee, hee). Had to read the material three times over, but I finally got it. I guess persistance does pay off.

Melanie