DevelopmentW2010.Lecture5notes

DevelopmentW2010.Lecture5notes - Development BIO 120 Winter...

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Development BIO 120 Winter 2010 Jeremy Lee Patrick Yuh Eva Murdock Lecture 5 Fertilization I. Types of Reproduction a. Sexual : reproduction associated with fusion of genetic material from different gametes. b. Asexual: reproduction without fusion of genetic material. 1. Parthenogenesis : reproduction without any need for male gametes. Examples include several species of lizard, and aphids (which, under certain conditions, reproduce sexually as well.) 2. Gynogenesis : reproduction requiring sperm to activate development of egg, but no fusion of genetic material. (Examples include some fish and salamanders.) c. Hybridogenesis : In this type of reproduction only female offspring are produced. (Fig. #1.1) To reproduce, a female mates with a male of another (though closely related) species, with both parents contributing genetic material to the exclusively female offspring. However, when a female produces gametes, there is a loss of her paternal genetic material (the genetic material she received from her father) during meiosis, meaning that all her gametes only contain her maternal genetic material (contributed by her mother.) Therefore, her offspring and all subsequent generations will pass on the identical maternal genetic material to their offspring; all generations will, therefore, be “hemiclones”, each having the identical genetic material making up half their genome. Examples of animals having this rare type of reproduction include certain fish and certain amphibians. II. Egg: major structures of egg found in most animals: (Fig. #1.2) a. Nucleus : In one of several possible stages of meiosis when fertilization begins; stage of meiosis at fertilization depends on species (see below.) b. Cytoplasm : includes yolk deposited by mother, used to nourish the egg and includes important substances for development (amount and distribution of yolk varies between different animals.) Cytoplasm, including yolk, contains: 1. Proteins: for egg and zygote metabolism. 2. Ribosomes and tRNAs : for protein synthesis. Fertilization is followed by a rapid increase in protein synthesis. Some ribosomes are made by the egg. 3. mRNAs : encode proteins that are synthesized after fertilization. 4. Morphogenetic factors : their localization in different parts of the egg specifies different regions of the egg and will initiate differentiation of cells in different parts of the embryo (these factors include specific mRNAs and proteins.) 5. Protective compounds : to prevent parasitization, predation, and/or damage to DNA. c. Cortex : region of cytoplasm just below plasma membrane; cortex has cortical granules , which are packed with digestive enzymes, mucopolysaccharides, glycoproteins, and hyalin protein.
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