Hybrids

[JesnieC]

"Selective breeding produces different varieties of crops that are homozygous for many genes. This can be disadvantegeous. Organisms that are homozygous for many genes are usually less vigourous than plants that are heterozygous for many genes. If a plant is a homozygous for many genes then there is more chance that it will display a disadvantageous characteristic due to a pair of recessive alleles."

-taken from Biology in Context The spectrum of Life by Peter Aubusson

Why does selective breeding produces different varieties of crops that are homozygous? How?

[Darby]

The simplified reason is that when you select for certain traits, you do two things: you select for certain alleles, and you are trying to produce a nondiverse population that breeds true. You're more likely to remove the non-preferred alleles, leaving just one type.

[canalon]

And then the seeds sold are F1 hybrids that are more vigorous than both parents, with the allele that you want.

[JesnieC]

You're more likely to remove the non-preferred alleles, leaving just one type.

I don't quite understand. If I remove the non-preferred alleles, then how come when a plant has many homozygous genes, its more likely to display bad characteristics due to recessive alleles?

[JackBean]

because you're selecting only some special feature, but with that you can select unwillingly other traits, which may be harmful. Or even your desired traits may be bad in some conditions.