Question

Stickleback fish that are deep in the ocean can experience a mutation wherein they experience a "loss-of-function" of their spikes. Heterozygotes actually look the same as homozygous wild types at this depth. If a homozygous deep-water wild type stickleback mated with a homozygous shallow-water wild type, what phenotypes would you expect to see? explain your answer and why you choose that answer. use crosses and diagrams where needed.

Answer 1

The heterozygotes look same as homozygous

This implies that the homozygous salt water stickleback fish is of dominant genes and they have functional spikes.

Now the shallow water wild type doesn't have functional spikes so they have reccesive homozygous gene.

Lets consider the dominant allele which produces pelvic spikes as 'P' and recessive one as 'p'

So now if we mate a homozygous deep-water wild type stickleback with a homozygous shallow-water wild type then we will get

	P	P
p	Pp	Pp
p	Pp	Pp

as the heterzygous resembles homozygous in marine type we will get phenotype of only marine type i.e they will have pelvic spikes.

So the phenotype ratio of with spike and without spike will be 1:0