(Sorry, we just love alliteration.)
Anyway,
unless you're our mom, or Sarah Palin, you might not argue with the
statement that we all came from hermaphrodites. But for years,
biologists have tried to figure out why and how the separate male and
female sexes evolved.
Now a fruit we already associate with sex may hold the answer.
[R]esearch
on wild strawberry plants is providing evidence for such a transition
and the emergence of sex, at least in plants. And the results... likely
apply to animals like us, the researchers say.
The study
showed that two genes located at different spots on a chromosome can
cast strawberry offspring as a single sex, a hermaphrodite or a neuter
(neither male nor female, and essentially sterile). The researchers
suspect the two genes could be responsible for one of the earliest
stages of the transition from asexual to sexual beings.
"All
of the animals and plants that are bi-sexual, or have two sexes, are
theorized to have evolved according to a particular set of steps," said
researcher Kim Lewers, a plant geneticist at the USDA's Genetic
Improvement of Fruits and Vegetables Lab in Maryland. "Until now, no
example had been found of the very earliest steps. Therefore, those
steps were undemonstrated to be true."
...
Flowering plants (plants equipped with reproductive organs) weren't
around until about 140 million to 180 million years ago. "Within
flowering plants, separate sexes is thought to have evolved from
hermaphroditism independently and repeatedly among lineages," said
researcher Rachel Spigler, a postdoctoral student at the University of
Pittsburgh, "so there is no one specific date for the evolution of sex
chromosomes in plants."
Lewers, Spigler and their colleagues spotted the genetic mutation in a
wild strawberry species, Fragaria virginiana, in which the evolution of
separate sexes is not complete. So in addition to male and female
strawberry plants, there are also some hermaphrodites and neutered
individuals.
Through lab work, including genetic mapping, the researchers figured out how the wacky mix of sexes, or no-sexes, worked.
The plants each have two proto-sex chromosomes. Two spots on each
proto-sex chromosome contain sex-determining genes, one that controls
sterility and fertility in males and another that does the same in
females.
Offspring that inherit both fertility versions are hemaphrodites and
can self-breed, while plants that inherit one fertility and one
sterility version become either male or female. (A female would result
from a sterile male and fertile female combination of genes.) Those
that get both sterility versions of the genes are considered neuters
and can't reproduce, so they ultimately die out.
While the two sex-determining genes are close to one another on the
proto-sex chromosomes, the researchers say they are not completely
linked. That's why the strawberry offspring can get such a wild mix of
the genes.
On our sex chromosomes, for instance, this mixing and matching is not
possible (or at least very rare), because the female chromosome is one
unit and so is the male sex chromosome.
Any science geeks out there want to put this in layman's terms for us?
[Live Science: Origin of Sex Pinned Down]
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