Question

You are an avid fan of mussels. In your journeys you discover a new group of mussels. Within this population, there are tasty mussels and not so tasty mussels. There is nothing in between. Being a science geek you determined through genetic analysis that the new flavor (tasty) is due to new mutations at two separate loci in a single metabolic pathway. Please use G/g and H/h for the two genes in the pathway. 1) What is (are) the trait(s) of interest? What are the observed phenotypes of this trait? 2) What genotype(s) are required for the new phenotype(s)? 3) How could those genotypes arise? 4) What is the proposed pathway? Be sure to have both genotypes and phenotypes on the pathway 5) What proportions of phenotypes would you expect from a cross of two heterozygotes (heterozygous at both loci)?

Answer 1

1)The trait here is the taste which can be either tasty or not pleasant to taste .

2)The dominant gene is usually considered to be the natural one and not the mutant gene.So let us assume that the phenotype of good taste appears when the dominant forms G and H are present .so the genotypes GGHH ,GgHh will be tasty and GgHh will be unpleasant to taste .

3)new mutant genotypes occur by mutation i.e a change in the copying sequence of the parent DNA .This could occue either due to radiations (ionising x-ray or non ionising u.v ray ),chemicals etc. For eg :U.V rays cause pyrimidine dimer formation ,hence a change in normal genetic composition .

4)pathway :mutation

5)cross between 2 heterozygotes will result in -

GgHh× GgHh

=GGHH

=GgHh

=GgHh

=GgHh

Phenotypic ratio :3:1

Genotypic ratio :1:2:2:1