Sex Determination in Ferns
...count the total number of “X” chromosomes present, special proteins trigger the appropriate set of genes to direct the correct, sexual growth of the embryo. Some organisms, however, do not depend on chromosomes to determine the gender of offspring. Instead, in these organisms, environmental factors, such as temperature, control the sexual development of phenotypes. For example, if a turtle’s eggs are incubated at low temperatures, they will hatch as males; on the other hand, egg incubation at high temperatures favors female development (Hurney et al., 2002). Although they don’t depend on either chromosomes or the environment for sexual determination of offspring, Ceratopteris richardii, commonly known as the C-fern, are generally used to explore the topic of sex determination. In Ceratopteris richardii, the diploid sporophyte undergoes meiosis to produce haploid spores. After the spore germinates, it develops into a multicellular, haploid gametophyte, which can be either male or hermaphroditic. The mature gametophytes then produce haploid eggs and or sperm, depending on its sex, by mitosis. Finally, the sperm fertilizes the egg, which results in a zygote that which mitotically divides to produce a diploid sporophyte. This constant change from gametophyte to sporophyte generation is called alternation of generations and occurs in most plants. In the experiment, the focus is to determine the effect that population density has on the number of male gametophytes produced in Ceratopteris richardii. Our hypothesis is that as the population density of Ceratopteris richardiiI increases, the number of male gametophytes will also increase (Hurney et al., 2002). Because the nature of this experiment was to see if the percentage of male gametophytes in a population is a function of population density, we analyzed different population samples by obtaining the total number of gametophytes and the number of male gametophytes in each population. And, as the graph based on our data below shows, on a plate with only 2 gametophytes in the population, there were no male gametophytes present, and as the population density rose, the percentage of male gametophytes also increased, until reaching a maximum of 45 males in a population of 123 gametophytes. The resulting data of our experiment clearly supports our hypothesis because as the population density of gametophytes per pl...