By Shirin K and Molly C-U, 7th grade (photos by Molly C-U)
On our final day with the zebrafish, all of the embryos hatched into larva! Curiously, out of the 101 zebrafish larvae in our entire class, all of them were wildtype, meaning that they developed pigment. Tracy Nelson from Penn returned to teach us why. The male, who was albino, was homozygous for the recessive allele (ww). (A gene codes for a particular trait, like pigment. An allele is a particularly variation of a gene, such as “no pigment” or albino.) The male evidently mated only with the wildtype female (not the albino female), whose genetic make-up was homozygous for the dominant allele (WW). Together, their children were heterozygous (different) for pigment, meaning that they carried one dominant allele (W) from their mother and one recessive allele (w) from their father. When this happens, the dominant allele takes over and is expressed in the phenotype. This made the larvae have the outward appearance of a wildtype zebrafish. Overall, we had a wonderful time studying the zebrafish this week.