Lab Report #2
November 9, 2011
Lab Report: Environmental Control of Sex Determination
Ceratopteris richardii, known as a C-fern has a lifecycle referred to as alteration of generations, which consist of neither haploid nor diploid dominant. C-ferns are homospours plants which are important in that they can produce hermaphrioditic gametophytes in order to be able to self fertilize. However, some of the homospourous C-ferns only produce male gametophytes .The life cycle of Ceratopteris richardii starts as a diploid sporophyte which then, by meiosis, produces haploid spores. These spores then undergo mitosis to produce a haploid gametophyte, which can be either hermaphrodite( producing eggs and sperm), or a male gametophyte (producing only sperm). Gametophytes then produce gametes by mitosis. The hermaphrodite gametophyte will produce both eggs and sperm,while, the male gametophyte will produce strictly sperm. The gametes from the hermaphrodite gametophyte fertilize one another producing a diploid zygote which grows by mitosis into a diploid sporophyte ready to start the cycle again (Lab Manual).
Chromosomal sex determination is determined by the inheritance of sex chromosomes, while, environmental sex determination is influenced by environmental factors such as temperature and parasite invasion(Lab Manual). Humans use the system of chromosomal sex determination by combining their X and Y chromosomes to produce a zygote determining the sexual phenotype in humans. Alligators use environmental sex determination when incubating their eggs.Temperature influences the sex of the offspring meaning; warmer incubating temperatures produce male development while cooler temperatures produce female development (Lab Manual).
Our hypothesis for the Ceratopteris richardii was that gametophyte population density influences sex determination. Our first prediction was that the percentage of male gametophytes would increase as the...