Biologych9 - 9.1 An Evolutionary View Asexual reproduction...

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9.1 An Evolutionary View Asexual reproduction → one alone produces offspring; each inherits same number and kinds of genes as parent = clones Genes → stretches of chromosomes – DNA molecules; contain all heritable info necessary to make new individuals Sexual reproduction → process involving meiosis, formation of gametes, and fertilization → union of nuclei of two gametes - In m ost sexual reproducers, first cell of new individual contains pairs of g en es on p airs of chromoso m es (one m at ernal, one pat ernal) - Two gen es of a p air m ay not b e identical b/c g en e’s m olecular structure can m ut at e so that two g en es paired in a p erson’s cells m ay “say” different things Allele → e ach unique m olecular form of the sa m e gen e * By sexual reproduction, offspring inherit n ew com bos of alleles, leading to * Variation in traits is a foundation for evolutionary chang e 9.2 Overview of Meiosis Partitions chromosomes into parcels TWICE prior to cytoplasmic division First step leading to formation of gametes Homologous chromosomes → pair of chromosomes with same length, shape and assortment of genes that line up with each other at meiosis - Body cells of hu m a ns have (23 + 2 3) ho mologous chromoso m es; so do g er m cells that give r hu m an g a m et es - After ger m cell finishes m eiosis, (23) chromoso m es will end up in those g a m et es, giving it a h aploid nu m b er (n) As in mitosis, duplicates DNA in interphas e a nd (2) DNA m olecules and associat ed proteins att ach ed at centrom ere, d e e ming the m sister chrom atids. Also similarly to mitosis, microtu of spindle app aratus m ove chromoso m es in prescribed directions. DIFFERENTLY however, in m eiosis chromoso m es go through TWO cons ecutive divisions that e nd with the form ation of four haploid nuclei -
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