Bio 3 Flashcards
Asexual and sexual reproduction
Asexual reproduction is common among unicellular organisms and rare in Vertebrates. Plants and fungi reproduce both sexually and asexually. For asexual reproduction Plants send runners and hydra perform budding. Fungi reproduce asexually via sporulation, budding or fragmentation. Advantages of asexual reproduction are that there is no need to possess mating behaviours, special anatomy or look for a mate. It also benefits organisms that invade new environments since finding a mate would be hard in that situation. Aphids reproduce asexually to make only females in favourable conditions allowing rapid population grow during these times. Disadvantages of sexual reproduction is that animals must have special anatomies that may attract predators. In humans, assisted reproductive technologies increase chances of reproductive success but are controversial. Amniocentesis is the removal of cells from a fluid filled sac surrounding a fetus. Multiple marker screening is testing for hormone levels that correspond to a disorder. In vitro fertilization is the fertilization of an egg outside the body with Intracytoplasmic sperm injection, injection of a single sperm into an egg. But this may cause hardening of the zona pellucida which laser assisted hatching prevents. The process of placing sperm into the uterus is artificial insemination, which had been used on other animals but is very costly.
Meiosis and mitosis
prophase, chromatin condenses into chromosomes, the nuclear envelope breaks and centrioles move to opposite sides of the cell with spindle fibres forming from them. During metaphase Chromosomes line up in the metaphase plate and the spindle fibres connect to their centromeres. Sister chromatids are pulled toward opposite ends of the cell in anaphase and in telophase vesicles made by the Golgi apparatus fuse causing the cell to splits in two via cytokinesis. Chromosomes decondense and are put in nuclear envelopes again. Meiosis has the same stages but goes through them twice. This is possible since in meiosis pairs of chromosomes called tetrads are formed via synapsis. They swap genetic material at a location called a chiasma. These then line up on the metaphase plate in metaphase I, but in anaphase I the chromosomes are pulled, with the sister chromatids still stuck together. The second time the cell goes through these phases is the same as for mitosis but has no G1 or S phase before it. Mitosis has one cell division that results in two genetically identical daughter cells that have the same number of chromosomes as the parent but meiosis has two divisions that result in four genetically distinct cells with half as many chromosomes as the parent. When cells from through meiosis join they make a zygote. Non disjunction disorders lead to monosomy where theres only one copy of a chromosome or trisomy where there are three copies. Infertility is more common and its caused by poor gamete production. Prenatal testing is testing for genetic disorders before birth, and it’s recommended for older pregnant women since risk increases with age.
DNA
Rosalind franklin found that DNA had a helix shape. The first model of DNA was made by James and Francis in 1953. DNA, existing as chromatin, is made of two strands of repeating segments called nucleotides that run in opposite directions and each contain a phosphate group, pentose sugar, and one of four nitrogenous bases. The purines, thymine and cytosine, form hydrogen bonds with the pyramidines, adenine and guanine. DNA is coiled around histones. this package form nucleosomes. When replicating the parts that are expressed are exons and the parts that are not are introns. Karyotypes are images of chromosomes, made by halting cell division at metaphase. Mutations can be insertion or deletion or inversion. They can be harmful or beneficial, but most are neither and accumulate until they become a source for genetic drift.
