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Lecture_Study_guide_1_Answers

Lecture_Study_guide_1_Answers - ZOL 320 2011 Answers for...

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ZOL 320 2011 Answers for Lecture Study Guide 1 1. Ontogeny is the development in the individual life cycle and is one part of the longer phylogenetic development of a species. The two are related because evolution of a new species requires the new genotype to be expressed sometime during ontogeny. 2. Genetic variation for sexual reproduction occurs through various types of mutation (point mutations or chromosomal mutations) in the germ line cells and then during meiosis generation of haploid gametes with unique combinations of the maternal and paternal chromosomes (independent assortment) and genetic exchange of homologous chromosomes (recombination = crossing over) on the autosomes of females and males and on the Xs in females. 3. There is a size increase in organisms starting with larger cells up to a limit, then an increase in multicellularity is seen and further in complexity of structures (or as a simple measure, the number of different cell types). 4. Von Baer was a keen comparative embryologist and noticed that the development of vertebrates of widely differing adult forms had strikingly similar features early in development. Embryos of a particular phylum, chordata for instance,although they may have different starting points (eggs of different sizes and composition) have a time early in development called the phylotypic stage in which the key characteristics of the phylum are present (notochord, dorsal hollow nerve tube, 3 pharyngeal arches). These structures have similar origins, shape and size at the phylotypic stage
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