Question

You would like to isolate a mutant fern capable of growing in the presence of cadmium, which is toxic to wild type ferns. What specific part of a fern plant would you treat with a mutagen called EMS in order to be able to identify mutant ferns within the same generation? Explain your strategy, which should be able to identify mutations right away (even if the mutation is recessive). Hint: Look at the life cycle of the fern

So in this question along with answering it, please draw punnet squares explaining the process going from sporangia to spores to gametophyte to sporophyte, when cadmium is treated and what happens when % die and % live, does that mean its recessive or dominant?

Answer 1

In ferns, gametophyte and sporophyte are equally dominant generations. They both are free-living, independent, and photosynthetic generations. They are not dependent on each other for nutrition.

The sporophyte produces sporangia on fertile fronds. The spore mother cells undergo meiosis to produce haploid spores. The haploid spores germinate and develop into a gametophyte.

To perform a mutagenesis screen, we can use fern spores.

Treat fern spores with EMS and grow them in the presence of Cadmium. Since spores are haploid, recessive mutations also exhibit mutant phenotype.

A = Dominant allele that confers resistance to Cadmium

a = Dominant allele that confers sensitivity to Cadmium

If a recessive mutation confers resistance, we have to self that gametophyte to obtain a homozygous recessive sporophyte.

a X a ---> aa

If a recessive mutation confers resistance, the presence of a single allele can cause resistance phenotype in the sporophyte.

A X a ---> Aa