I would like some help with a question about Mendelian inheritance, based on the following information (I assume this is autosomal and not sex linked):
-- Start of information --
"As flatfish (Pleuronectiformes) develop, they lose their bilateral symmetry. One of their eyes migrates across the top of the head, so that both eyes end up adjacent on the same side of the head. As a result, the adult fish is able to lie flat on its side on the sea floor with both eyes facing up. In some species of flatfish the right eye migrates to the left side of the head (they are left-eyed); in other species the left eye migrates to the right side of the head (they
In one species of flatfish, the starry flounder (Platichthys stellatus), different populations have different proportions of left-eyed and right-eyed individuals. Off the west coast of the USA the population is evenly divided between left-eyed and right-eyed individuals. However, in the north Pacific, midway between the USA and Japan, 70% of the population is left-eyed and in Japanese waters all the starry flounder are left-eyed.
Consider the following hypotheses (I – III) about the starry flounder. The hypotheses assume that a single gene locus determines the final location of the eyes on the head.
I. The Japanese fish are homozygous for a dominant left-eyed allele (LL), whereas west coast fish are homozygous for a neutral allele (ll) and have an equal chance of developing into either left- or right-eyed individuals.
II. The Japanese fish are homozygous for the left-eyed allele (LL), whereas in the west coast fish both left-eyed (L) and right-eyed (R) alleles occur in equal proportions. Heterozygous individuals (LR) have an equal chance of developing into either the left- or right-eyed form.
III. There are three alleles of the controlling gene: the left-eyed allele (L) is dominant to both the right-eyed allele (l) and the neutral allele (l’). Further, the right-eyed allele is dominant to the neutral allele. Fish that are homozygous neutral (l’l’) have an equal chance of developing into right- or left-eyed individuals."
-- End of information --
The question says: When a left-eyed mid-Pacific female and a right-eyed west coast male were crossed and the offspring were all kept in standard laboratory conditions on the west coast of the USA, 50% of the thousands of offspring were right-eyed and 50% were left-eyed. Of the following this result completely rules out:
A hypothesis I.
B hypothesis II.
C hypothesis III.
D none of the hypotheses
The 3 hypotheses only talk about Japanese fish and west coast fish, there is no mention of mid Pacific fish, and, if it is talking about the North Pacific fish, the info state that "However, in the north Pacific, midway between the USA and Japan, 70% of the population is left-eyed and in Japanese waters all the starry flounder are left eyed."
From this we infer that:
- the 70% part refer to the non-Japanese fish due to the word 'and'
- the non-Japanese fish must be the north Pacific fish since there are no other fish mentioned.
- What are mid Pacific fish? And what are their genotypes/alleles?
- Some fish have equal chances of being left or right eyed, so that specific genotype represents 12.5% and 12.5% where each square of a Punnett square is 25%. So you add 25% + 25% and + or - 12.5% or 25%. Therefore the closest thing to 70% is 50+12.5 = 62.5% or 50+25% = 75%, either under or over, when trying to determine how to get the mid Pacific fish.
So I can't get the 70% and still don't know what mid Pacific fish are.
I know how to do Punnett squares. But my issue is the wording of this question. It says "left-eyed mid-Pacific". None of the genotypes mentioned in any of the hypotheses mention Mid-Pacific. Unless it means midway between Japan and USA, which the question info state is NORTH Pacific.
So my question is, do we need to and if so how, to reverse-guess the female North Pacific fish' genotype. Or if we don't, how to do this question.
My reasoning is, the only way Hyp 1 can create a right eyed fish, as opposed to Hyp 2 (which say R is right eyed) is if I take each hyp 1 as it is (ie, the available alleles are LL for homozygous dominant left and ll for homozygous neutral where there is a 50:50 chance of being either left or right), without trying to figure out what a Mid Pacific fish is (I believe if a Mid Pacific fish is a cross between a West Coast fish and a North Pacific fish, then we need to look at all the possible combinations of this, in which the result is 70 left eyed. There are 2 problems with this, one this is a practise exam question where you have 1.5 minutes per question, and 2, there is no way to get 70 from adding or subtracting 12.5, 25, and 50.) then, Hyp 1 says LL and ll. A cross between that is 100% Ll, which is 100% Left, ruling it out instantly since we want 50% left and 50% right.
However, the answer was D, no hypothesis is ruled out.
This is a Punnett square I did for each combination listed in the 3 hypotheses, based on a West Cost male and a Japanese fish.
(So, in total we have 4 fish types, the West Cost male and a Japanese fish mentioned in the hypotheses, the North Pacific fish mentioned in the information and the Mid Pacific asked for in the question.)
Can someone help explain this?