Expert: Dana Krempels, Ph.D. - 10/13/2010

Question
I have to present the path of change and reduction of the gametophyte from mosses through ferns to higher plants.  I have to discuss what advantage having a dominant sporophyte and a parasitic gametophyte gives to modern plants living in a terrestial environment. I have been working on this for 2 days:  I need help, this is what I have so far:
Burophytes the sporophyte was dependent on gametophyte for reproduction.  Then in ferns the large sporophyte and a small independent gametophyte.  Now in seed plants the gametophyte is dependent on the sporophyte, flowering plants the male gametophyte develops in the pollen and the female in the ovule.  Gametophyte are reduced to a afew cells and they are dependent on those cells for thier nutrition to go onto the sporophyte phase.
Advantages:
Sporophyte is a diploid not haploid so it has 2 sets of genes.  Male gametophyte is let out in the plants seed and protected by the sporophyte tissue.  The embryo is protected and stays protected for a long time until the conditions are good enough to germinate.  Female gametophyte is much smaller so it can be enclosed & completely protected in the sporophyte tissue.  Spores have a shorter life than seeds.  I know this sounds crazy, but I don't understand any of this.  The more I look the more I get confused.  So you can see I'm not trying to cheat I need help and guidance.

Answer
Dear Kathy,

I have a web site you can use as a reference, but don't use this for your presentation without citing the source.  I hope it will help you understand alternation of generations with an animal metaphor/analogy I created.  A little gross, but I think it gets the point across:

http://www.bio.miami.edu/dana/dox/altgen_new.html

Hope this helps you understand so you can create a good, original project.

Good luck,

Dana