What does the concept of "extreme heterozygosity" mean?
I first encountered this concept in "The Drunken Botanist". They describe that when planting a seed from, say, a 'red delicious' which was pollinated by another 'red delicious' does not guarantee growing another 'red delicious' tree. The author goes so far to say that the new tree may have almost none of its parent traits, and may barely resemble any other breed whatsoever. They argue this is caused by extreme heterozygosity.
I later found the concept of extreme heterozygosity the Wiki page for "apple"
This is because seedling apples are an example of "extreme heterozygotes", in that rather than inheriting DNA from their parents to create a new apple with those characteristics, they are instead significantly different from their parents.
We conclude that the extreme heterozygosity in C. savignyi is caused by a large effective population size and not an elevated mutation rate.
My understanding of population genetics (allele frequencies and patterns of dominance)
I understand homozygous diploid pairs, like pp or PP, and heterozygous pairs like pP and Pp, and hetero/homozygous dominance and recession. I also found an interesting paper on sea squirts to work through later that suggests why extreme heterozygousity is popular in large population sizes. What I can't seem to find is exactly how "extreme heterozygousity" works. How is this different than ordinary heterozygous? Is there an entirely different context I'm missing out on? The only way I can imagine a more "extreme" heterozygosity is with triploid mismatched pairs, which can't be right. So how does the process work and what exactly defines it?