Okay.
To answer this question, we first need to know about two things:
1. Natural selection
2. Phenotype
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NATURAL SELECTION is where the environment determines which organisms live, and which ones die.
For example...
pretend that it's freezing cold outside.
And that there are two types of animals:
ones WITH fur,
and ones WITHOUT fur.
Which ones will die out?
The ones WITHOUT fur would die out,
because the cold would kill them.
That's an example of NATURAL SELECTION.
NATURE determines who lives, and who dies.
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PHENOTYPE can be another word for APPEARANCE.
For example,
TALL is a phenotype.
SHORT is a phenotype.
BROWN EYES is a phenotype.
RED HAIR is a phenotype.
THICK FUR is a phenotype.
NO FUR is a phenotype.
PHENOTYPE can mean APPEARANCE.
The way that an organism looks.
You see?
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Now, let's go to our question:
"Which of the following explains why natural selection acts on the phenotype of an organism instead of its genotype?"
NATURAL SELECTION, again, is where NATURE, and the ENVIRONMENT, determines who lives, and who dies.
It decides this, based on how an organism LOOKS.
In order words,
nature decides who lives, and who dies, based on an organism's PHENOTYPE.
Remember the example I used?
If it's freezing cold outside,
then nature will determine that the ones WITHOUT FUR would die.
And the ones WITH FUR would live.
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Here's another example:
Pretend that we're on an island.
This island has two kinds of birds:
ones WITH sharp beaks,
and ones WITHOUT sharp beaks.
This island also has one food source:
nuts, with hard shells.
In order to crack open the hard shells,
a bird would need a sharp beak.
So..which birds would live,
and which ones would die?
The ones WITHOUT sharp beaks would die,
because without sharp beaks,
they wouldn't be able to crack open the hard shelled nuts, and eat!
That is another example of how NATURAL SELECTION determines who lives, and who dies.
And once again, it determines this, based on the organism's PHENOTYPE, or APPEARANCE.
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Now, you think you can use this information to help you pick out the correct answer?
