In the pathway depicted above, pigment molecules are created through chemical re

Question

In the pathway depicted above, pigment molecules are created through chemical reactions catalyzed by the various enzymes, encoded by their respective genes. The white pigments do not affect color. Pigments can combine to create new colors (orange, green, and purple). Each enzyme has a dominant allele and recessive allele. Genes A – D, when at least one wild type allele is present, catalyze their respective reactions. The intermediate molecules (yellow and red) are completely converted into products if the enzyme is present.

Enzyme D can convert red pigment into yellow pigment, when at least one wild type allele is present.

Gene E is a dominant inhibitor of enzyme B; when at least one dominant allele of E is present, the B enzyme will not function.

What full-genotype would you self-cross to achieve the following phenotypic ratios? Genes do not need to be homozygous. Write the answer the format: "AABbccDDee" with genes listed in alphabetical order and no spaces between genes. Because these are dihybrid or monohybrid crosses, only list the self-crossed parent once. Some questions have multiple possible answers.

For example: 9 Yelow : 3 Bue : 3 Orange : 1 Purple -->. AABBCCDdEe

A. 9 blue: 3 yellow: 4 white -->

B. 9 purple: 3 orange: 3 blue: 1 yellow -->

C. 15 yellow: 1 white -->

D. 13 yellow: 3 blue -->

E. 9 orange: 3 red: 3 yellow: 1 white -->

F. 12 yellow: 4 red -->

Explanation / Answer

To get these answers, we need to think about genes that will be active in order to form the products.

A. We need blue yellow and white. So, upper pathway should be active and pathway through red should be inactive. Since, we need both blue and yellow, therefore, the enzyme for the formation of blue will be heterozygous. Similarly, we want both yellow and white. So, the gene forming yellow would be heterozygous too. The red pathway needs to be shut down. So, the gene forming the red color should be homozygous recessive. The gene forming yellow from red can be in any form. As we need blue, the gene E should be recessive. So, the required genotype is AaBbccddee or AaBbccDdee or AaBbccDDee.

B. We need purple orange blue and yellow. As there is no white, the A and C are homozygous dominant. Red and blue gives purple (A_B_C_ee) and red and yellow gives orange (A_C_dd). So, the genotype will be AABbCCDdee.

C. We want most of them yellow and just 1 white. For that pathway after yellow should be blocked. So, it will be EE or bb. All red should convert to yellow. So, it is DD. 1 out of 16 are white. So, it will be only if 2 recessives (aa and cc) are present. So, A and C are heterozygous. The genotype can be AaBBCcDDEE, AaBbCcDDEE, AabbCcDDEE, AabbCcDDEe, AabbCcDDee.

D. Yellow and blue will come if E is heterozygous i.e. Ee or B is hetterozygous. All rest pathways should come to Yellow. An extra yellow will also form when B is heterozygous as it will not be able to convert to blue when bb comes in progeny. So, the genotype would be AABbCCDDEe.

E. Orange red yelllow and white will be formed when EE is present or bb is present in all progenies to block the conversion to blue. Orange will be formed when yellow is formed from above pathway and red from below pathway. This requires dd in progeny and hence, parent is Dd or dd. We also require one white color and 3 each of red and yellow. THis can happen only if upper and below pathways are independent. So, it should be dd in parents. Also, white will be formed by aa and cc so, parents must be heterozygous for these.Hence, the genotypes are AabbCcddEe, AabbCcddEE, AabbCcddee, AaBBCcddEE and AaBbCcddEE.

F. For yellow and red to appear, the D enzyme must be heterozygous and blue formation should be blocked. So, the genotype would be AAbbCCDdEE, AAbbCCDdEe, AAbbCCDdee, AABbCCDdEE and AABBCCDdEE.

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