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Effects of Climate Change on Corals
Published in Donat-P. Häder, Kunshan Gao, Aquatic Ecosystems in a Changing Climate, 2018
Another approach of anthropogenically assisted coral survival is based on sexual reproduction. This endeavour takes advantage of the synchronized spawning of the gametes (Brady et al. 2009). In this method, eggs and sperms are collected underwater in tubes. Fertilization is brought about by bringing the gametes together. This procedure has the significant advantage that all eggs and sperm cells have a high chance of finding a sexual partner, while in nature the gametes are diluted in the vast ocean despite of the synchronized release. The resulting larvae are very small and run a high risk of being eaten in the wild. Another problem is that natural fertilization in the ocean can be inhibited by accidental oil spills (Negri and Heyward 2000). In Acropora millepora an inhibition by 25% was observed in the fertilization rate by exposure to very low concentrations (0.0721 mg/L) of total hydrocarbons. Also trace concentrations of heavy metals, such as copper, lead, zinc, cadmium, and nickel decreased the fertilization rate at concentrations of 15 to 40 μg/L (Reichelt-Brushett and Harrison 2005, Reichelt-Brushett and Michalek-Wagner 2005). Also reduced salinity decreases the success of fertilization and larval survival as shown in Acropora millepora and Platygyra daedalea (Scott et al. 2013) as well as by high inorganic nutrient concentrations (Lam et al. 2015).
Naturally Occurring Polymers—Animals
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
A brief review of the meiosis process is in order. In the first step, the chromosomes of a cell containing six chromosomes, three homologous pairs, are replicated and held together at their centromeres. Each replicated double-stranded DNA is called a chromatid or “sister chromatid,” In the next step, the three homologous sets of chromatids align, forming tetrads that are held together by covalent bonding at homologous junctions called chiasmata. Crossovers, recombinations, occur such that the two tethered chromosomes segregate properly to opposite poles in the next step. This is followed by the homologous pairs separating and migrating toward opposite poles of the dividing cells. This first meiotic division gives two daughter cells, each with three pairs of chromatids. The homologous pairs again line up across the center or equator of the cell in preparation for separation of the chromatids, chromosomes. The second meiotic division produces four haploid daughter cells that can act as gametes. Each cell has three chromosomes, half the number of the diploid cell. The chromosomes have resorted and recombined.
Population dynamics
Published in A. W. Jayawardena, Environmental and Hydrological Systems Modelling, 2013
Division of cells is by binary fission, mitosis, and meiosis. Prokaryotic cells that lack a nucleus divide by binary fission. Eukaryotic cells divide by mitosis or meiosis. Mitosis is nuclear division followed by division of the cell called kinesis. The cell duplicates the chromosomes in its nucleus to generate two identical daughter cells. Both these processes are asexual. Meiosis is the process of reduction division in which the number of chromosomes per cell is cut in half. Meiosis is essential for sexual reproduction and therefore occurs in all eukaryotes, including single-celled organisms that reproduce sexually. In diploid cells, specialized cells called gametes (egg and sperm) are created through meiosis. Then, the sperm and egg join together to form a single cell. Cell growth cycle is a hot area of research because of its medical applications. Cancer cells grow exponentially, and an understanding of the growth cycle is needed to control their proliferation through drugs.
Producing Parenthood: Islamic Bioethical Perspectives & Normative Implications
Published in The New Bioethics, 2020
Aasim I. Padela, Katherine Klima, Rosie Duivenbode
To identify specific contestations about parenthood we will discuss three distinct forms of third-party involvement in reproduction and use a case scenario to work through the bioethical perspectives. Consider an infertile married couple, comprised of a male (M) and female (F) partner. If they opt for gamete donation, a third party (the gamete donor) contributes genetic material in the form of sperm (donor S), ova (donor O), or ova cytoplasm containing mitochondrial DNA, while the intended mother (F) gestates the fetus. In the case of gestational surrogacy, the surrogate (G) gestates an embryo produced via IVF with the gametes of the infertile couple (M and F). The legal husband (H) of the surrogate (G) is also part of our case study. Lastly, in the case of uterus transplantation the infertile couple (M and F) contribute the genetic material and the female (F) carries the child. Yet, the reproduction remains dependent on a third party (the uterus donor). Each of these treatment options poses unique challenges to what constitutes parenthood.