Hetero-Fertilization; or, My Two Dads

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Karl K
Posts: 1383
Joined: Sat Jun 02, 2012 4:49 pm

Hetero-Fertilization; or, My Two Dads

Post: # 72923Post Karl K
Mon Apr 26, 2021 12:42 pm

Back in the 18th century, there was some discussion of the possibility of superfoetation (or superfetation). Is it possible for a pregnant female (animal or human) to be impregnated by another male.

T. A. Knight (1799), the noted English horticulturist experimented to determine whether superfoetation is possible in plants. He was a bit handicapped in his effort because it would be a long time before the pollen tube was discovered. He wrote, " it appears by no means impossible, that the explosion of 2 vesicles of farina, at the same moment, taken from different plants, may afford seeds, as I have supposed, of common parentage; "

Then he got around to my subject: "Another species of superfoetation, if I have justly applied that term to a process in which 1 seed appears to have been the offspring of 2 males, has occurred to me so often, as to remove all possibility of doubt as to its existence;"

Now we must leap forward to the 20th century, when Sprague (1927) demonstrated that one kernel of corn (maize) may have an embryo derived from one pollen parent, and the endosperm from another.

Over the years since the discovery of double-fertilization, it has become apparent that the endosperm plays a critical role in the development of the embryo. It is not a simple matter of nutrition. And this is why reciprocal crosses, involving parents that are geographically or phylogenetically, are so often different in their development. This effect should not be confused with cytoplasmic inheritance, which is a different matter altogether.

Crosses between distinct species, and even varieties with different chromosome numbers, sometimes fail because endosoperm does not develop properly. It may grow for a time, then begin to deteriorate ... eventually killing the embryo. Embryo rescue may save the cross.

Or, the developmental conflict may strike the embryo, leaving endosperm rescue as the option.

But hetero-fertilization some times saves the day. This seems to explain why certain wide crosses work out in "the wild", but fail when a single pollination by a single pollen parent is used. Of course, at least two types of pollen must be used, and the research of Rotarenco and Eder (2003) indicated that the two pollinations occurred sequentially, not simultaneously.

The basics of Double Fertilization are described and illustrated here:
http://bulbnrose.x10.mx/Heredity/Double ... ouble.html

And more info on Hetero-Fertilization along with an expanded bibliography are here:

Karl K
Posts: 1383
Joined: Sat Jun 02, 2012 4:49 pm

Re: Hetero-Fertilization; or, My Two Dads

Post: # 72927Post Karl K
Fri Apr 30, 2021 12:48 pm

Nicolas (1933) described a useful example of differences in reciprocal crosses, influenced by the very different endosperms.

"For instance, a cross of Hortulanus Budde x R. Moyesi gave me slightly modified Hybrid Tea types where Moyesi was only recognized by the weird red single blooms and smaller foliage, while one almost totally mother type revealed the pollen parent only by the queer bottle shape of Moyesi fruits. The reciprocal cross (R. Moyesi x Hortulanus Budde) produced plants almost as uncouth and crude as Moyesi."

HTs are typically tetraploid (4X). The pollen and ova will carry 14 chromosomes (2X). The central cell, however, will carry 28 (X). When pollinated by the hexaploid (6X) Rosa moyesii, the pollen and ova will carry 21 chromosomes (3X). Thus, the embryo should have 14 chromosomes from the HT parent, 21 from Moyesii. The endosperm, to the contrary, will have 28 HT and 21 Moyesii. Cleary the HT (seed) parent will have more influence on the developing embryo.

In the reciprocal cross, the embryo will have roughly the same inheritance, the the endosperm will have 42 Moyesii chromosomes and a mere 14 from the HT parent. No wonder the offspring were so "uncouth and crude".

Now, if hetero-fertilization should occur, assuming the HT as the seed parent, then an endosperm with 21 HT chromosomes would be "training" the embryo strongly in the direction of the HT type.

Before I forget it again, this paper by Heslop-Harrison is a must read for understanding much of heredity that was largely ignored by the neo-mendelists, and condemned by them when someone outside their charmed circle dared to mention the facts.

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