Question

In: Biology

You have a true-breeding wild-type strain of fish that have rounded scales. A colleague of yours...

You have a true-breeding wild-type strain of fish that have rounded scales. A colleague of yours gives you a mutant fish that is naked (no scales). When you cross your wild type fish with your friends naked fish all of the F1 offspring are wild type.

a) From this information alone, what are the possible genotypes of your fish, your friend’s fish (the parents) and their offspring?

b) Based on these hypothesized genotypes what do you expect the outcome of a cross between the F1's to be?

You then cross the F1s you get the following results:

300 wild type fish,

97 fish with linear scales

132 naked fish.

c) Are these results consistent with your hypothesis above? If you think it is consistent test your results with chi squared test and discus the meaning of your results.

d) If the observed results are not consistent with your expected results, what is an alternative hypothesis (an alternative pattern of inheritance) that might explain these results?

e) Test this with a chi-squared test and discuss the results.

Expert Solution

A.

My fish = FF

Friend's fish = ff

Progeny fish = Ff

B.

Ff × Ff

Gametes	F	f
F	FF	Ff
f	Ff	ff

Normal fishes = 3/4

# = 3/4 × 451 = 338.25

Mutant fishes = 1/4

# = 1/4 × 451 = 112.75

Linear fishes = 0

Total # fishes = 300 + 132 + 97 = 451

Chi square test

Phenotype	#observed	#expected	(O-E)^2/E
WT	300	338.25	4.328
Linear	97	0	0
Mutant	132	112.75	3.286

Calculated chi square value = 4.328 + 3.286 = 7.614

Degrees of freedom = 3 - 1 = 2

p value = 0.025 to 0.05

p value is pess than 0.05.

We will reject null hypothesis.

Alternative hypothesis - The wild type allele is not completely dominant to the recessive allele. It is because we can see a third phenotype in heterozygotes. The heterozygotes are showing and intermediate phenotype between the two extreme phenotype. This is possible in case of incomplete dominance. In this type of inheritance, the wild type allele is incompletely dominant over the recessive allele and is therefore not able to express itself in heterozygotes.

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gladiator answered 2 years ago

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