2/14 free write- Bio lab report intro

Sex determination can be controlled by factors such as chromosomal and environmental. Sex chromosomes contain genetic information that determines the sexual development of the embryo. An example of this is the X-Y system of sex determination in humans which determines whether they are male or female. In this system, the Y chromosome codes for the initiation of male phenotype, while the X chromosome codes for the initiation of female genotype. An example of environmental sex determination would be alligators. The alligators’ egg sex is determined by the temperature the eggs are laid in. The warmer incubation temperature favors male development and the cooler incubation temperature favors female development (Hurney et. al, 2014).

            The C-fern (or Ceratopteris richardii) is a tropical homosporous fern which produces haploid single-celled spores that contain no sex chromosomes. These spores, however, can differentiate into male or hermaphrodite gametophytes. These gametophytes produce haploid gametes through mitosis. As a final step, the fertilization of the egg and the sperm results in a zygote that divides via mitosis to form diploid sporophyte. Ferns present alternation of generations which means sporophytes and gametophytes alternate between stages. The fact that the C-fern is a homosporous plant that produces two different types of gametophytes (male or hermaphrodite) is very significant in the life cycle of the fern. Because of this ability, the sex of the C-fern is determined by the population density it is placed in.

            In accordance with this ability, the lab experiment conducted tests if the sexual phenotype of the gametophyte generation of C-ferns are influenced by population density and whether a high population density produces more males or hermaphrodites. For this experiment, it is hypothesized that gametophyte population density influences sex determination of Ceratopteris richardii. Two predictions are that the higher the population density, the more male gametophytes will be present or the higher the population density, less male gametophytes will be present.


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