Answer:
1/4
Explanation:
Given that the F2 cross produces offspring according to the expected 9:3:3:1 ratio.
YyRr X YyRr:
Let us break the dihybrid cross into individual monohybrid crosses.
Yy X Yy :
Y y
Y YY Yy
y Yy yy
2/4 or 1/2 of the offspring are heterozygous for the trait.
Similarly, in Rr X Rr cross, 1/2 of the offspring are heterozygous for the trait.
Together, 1/2 * 1/2 = 1/4 of F2 plants are expected to be heterozygous for both traits.
Answer:
during the Cambrian Period of the Paleozoic Era.
Explanation:
The Paleozoic is the earliest era (of three) of the Phanerozoic Eon and is composed of six geologic periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian (in that order from earliest to the latest). Fish first appeared about 530 million years ago during the Cambrian explosion.
<span>The tracheae possibly have evolved directly from the book lungs</span>
Explanation:
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