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University of Toronto St. George
Christopher Watts

- modern evolutionary biology is based on genetics Chromosomes and Genetic Materials - there are 2 types of cells in any living organism: prokaryotic and eukaryotic cells - the main difference is that prokaryotic cells, such as bacteria, lack a cell nucleus and are unicellular, while eukaryotic cells have a nucleus and can be unicellular or multicellular. - eukaryotic cells can form complex systems in multicellular organisms, such as humans. - prokaryotic cells cannot form multicellular organisms Eukaryotic Cells - within the nucleus of these cells are chromosomes - chromosomes are DNA molecules that contain hereditary information - each eukaryotic cell can duplicate itself and its chromosomes in a complex process known as mitosis, where cells are divided into two identical daughter cells with the same number of chromosomes as the parent cell. - more important to inheritance, and therefore evolutionary processes, is meiosis, in which cellular divisions result in daughter cells with half the chromosomes of the parent cell and which also results in the formation of haploid cells that determine an organisms sex (i.e. sex cells or gametes) - meiosis provides the hereditary material passed between generations in sexually reproducing species, like humans. - humans typically have 23 pairs of chromosomes (46 chromosomes) in a diploid cell. - a diploid cell is a cell containing two sets of chromosomes, or one set inherited from each parent. - females have an XX set of sex chromosomes and males have an XY set of sex chromosomes. - when a gamete is made, the chromosomes first find their matched partners and exchange some genetic materials with each other in a process called recombination, or crossing over. This happens before fertilization takes place. - DNA strands are wrapped around spool-like proteins called histones, to form a chromosome. - DNA contains the genetic blueprint necessary for specifying the sequence of amino acids that comprise proteins. Mutation: The Ultimate Source of Genetic Variation
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