You identify a rare purple plumed parrot. when you cross the parrot to a true breeding white parrot, you get ½ white and ½ purple parrots. when you cross two purple parrots you get 1/3 white parrots and 2/3 purple parrots. which of the following best explains this result? a. the purple allele is lethal in the homozygous state. b. white is dominant to purple. c. the white allele is lethal in the homozygous state. d. the purple allele is lethal in the heterozygous state.

a. The purple allele is lethal in the homozygous state

Explanation:

You cross a purple parrot with a true breeding (homozygous) white parrot and you get 1/2 purple parrots and 1/2 white parrots. This result can only happen if the purple parrot is heterozygous and the white parrot is homozygous recessive (if any of the parents had been homozygous dominant, 100% of the offspring would have had the dominant phenotype).

Then: Pp (purple) X pp (white) ---> 1/2 Pp, 1/2 pp

When you cross two purple parrots you get 1/3 white parrots and 2/3 purple parrots. The 2:1 phenotypic ratio is typical of a lethal allele in the homozygous state.

In a cross of two purple parrots: Pp

X Pp, one would expect the genotypic ratios 1 PP : 2 Pp : 1pp and the phenotypic ratios 3 Purple : 1 white.

But the PP genotype is lethal, so those individuals die and the only purple parrots we see are the heterozygous ones.

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hope this you! : )

(i popped my answer into google translate so it may be a bit wonky)

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.