In which phase of a muscle twitch are voltage-gated calcium channels first activated in order to release calcium from the SR

The image shows embryos of three vertebrate classes

In fruit flies, gray bodies (g) are dominant over black bodies (g), and brown pigments (n) are dominant over yellow pigments (n). each individual possesses two alleles for each trait. if a fly that is homozygous dominant for both traits is crossed with a fly that is homozygous recessive for both traits, what is the predicted genotype of the offspring.

How can antibodies "remember" a particular bacterial invader or "antigen" on that invader?