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Genetics with taxonomic implications

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Posted by: RichardFHoyer at Mon Aug 9 19:46:58 2004  [ Report Abuse ] [ Email Message ] [ Show All Posts by RichardFHoyer ]  
   

Any geneticists on board?

There are two reasonably distinct size morphs in C. bottae, a dwarf form found at the southern extreme of the species' range in Calif. and the large morph that exists in the remainder of the species' range in North America from Tulare county, Calif. northward and eastward.

Dwarf C. bottae produce small neonates that range up to about 8 5/8" with a mean length between 7 1/2 to 8" Don't have a large enough sample from many regions of the large morph but locally in Oregon and information on litters from other regions indicate that neonates are generally 9" or above in length. The mean length for the local large morph females is slightly over 10".

In 1996 and 1999 I crossed dwarf males x large morph females. The size of resultant neonates were within the large morph neonate lengths. I completed a similar cross this year with the same results.

I should mention that one of the defining features between the two morphs is that maximum lengths of the dwarf form females is around 22" whereas all population of the large morph for which I have a reasonable sample have had females of 25" or longer.

A hybrid female from the 1996 cross became sexually mature during last summer just before her 7th birthday and at around 22 1/2" in length. By last Oct. she attained the robust condition necessary to carry a litter this year. This spring I backcrossed her to two dwarf males.

I had formed a hypothesis that what has kept the two morphs distinct where they must intergrade in the southern Sierras is that large morph females produce large ova resulting in large neonates and dwarf females produce smaller ova that result in much smaller neontates. Since ova are developing well before mating occurs and then the sperm are stored until ovulation, I have, perhaps erroneously, discounted influence of the parent males.

The hypothesis was simply conjecture except for the results of the dwarf male x large morph female crosses which have produced large morph neonates.

The hypothsis just bit the dust three days ago when the hybrid female produced her litter of one slug and 5 young--- all of which were dwarf.

Is there anyone that knows of a genetic explanation? Is anyone aware of 'delayed maternal inheretance'? After fertilization, could factors in the male sperm affect the eventual size of the developing embryos? it that were the case, then just by change alone once in awhile one could expect the results obtained. Yet that would suggest simple Mendelian inheretance and it would have been my guess that polygenic inheretance would be involved with size factors.

Yet despite just this one sample, the outcome suggests some sort of discrete pattern of inheretance.

In 2006 when this female is again in reproductive condition, do I make the same backcross to hopefully verify current results and increase my sample or should I make the reciprocal backcross to a large morph male?

Stumped! Richard F. Hoyer


   

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>> Next Message:  RE: Genetics with taxonomic implications - CKing, Tue Aug 10 01:09:20 2004