Answer:
We know that the color of jellyfish is controlled by codominance inheritance pattern and yellow Y and blue B are two alleles and in case of heterozygous the goober or green color occurs then,
If Yellow jellyfish is crossed with goober, that is, YY X YB.
the punnett square will be -
Y Y
Y YY YY
B YB YB
The possible genotype of offspring will be YY, and YB and therefore, the possible phenotype of offspring will be Yellow, and Green. The Percentage of yellow offspring will be 50% as two out of four are dominant for Y allele and two heterozygous conditions that is 50 % and as there are two copies B alleles are not present so zero percent of blue color.