LESSON

Sex Determination in Ferns

QUESTION

What influences sex determination in ferns?

Introduction

          Sexual reproduction is important for the survival of a species.  The sexual types— the male and the female— are necessary for the production of sperm and egg, which when fused allows the formation of different combinations of genetic traits in each new generation.  Sex in ferns is associated with the production of sperm and eggs by sexually distinct, small, free-living gametophytes.  Quite naturally the following questions can be asked: From which part of the fern plant does the male sex organ develop?  What controls the development of the male sex organ in ferns?

          The first set of explanations should include the following:

1. The life cycle of the fern is composed of two alternating generations, i.e., the sporophyte generation and gametophyte generation.
   

2. The gametophytes from which the male and female sex organs develop are free-living organisms that live independently.
   

3. The male sex organs are produced nearer the posterior portion of the gametophyte at the rhizoidal region.

          And the second explanation should be:

1. Hormonal influences determine the development of the male sex organs.

1. To observe the development of the male sex organ in fern.

2. To make a culture of gametophyte.

3. To generate hypotheses about factors that influence the development of the male sex organ in fern.

agar cultures of gametophytes
hand lenses/microscopes

1. Provide students with two culture plates inoculated with spores: one plate containing low spore density, and the other containing high spore density.

2. Maintain the culture plates in a well-ventilated area with enough supply of light (the use of controlled environment chambers is recommended).

3. Have students carefully observe the cultures periodically, and the gametophyte development and the development of the male sex organ.

4. Have students record notes and make sketches to help them remember their thoughts and observations.

1. Do you observe any changes in the spores sown on Day 0 and 4?
   

2. Do you observe any differences between culture A (low spore  density) and  culture B (high spore density)?
   

3. What do you predict the gametophyte might look like after germination  in culture A? in culture B?
   

4. Can you identify the antheridia (male sex organ)?
   

5. Can you find any differences in development of the antheridia?
   

6. In which culture (A or B) was the result similar to that of gametophyte cultures treated with gibberellin (refer to the slide pictures