Chapter 9 - 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 most sexual reproducers, first cell of new individual contains pairs of genes on pairs of chromosomes (one maternal, one paternal) - Two genes of a pair may not be identical b/c gene’s molecular structure can mutate so that two genes paired in a person’s cells may “say” different things about a trait Allele → each unique molecular form of the same gene * By sexual reproduction, offspring inherit new combos of alleles, leading to variations in details * Variation in traits is a foundation for evolutionary change 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 humans have (23+23) homologous chromosomes; so do germ cells that give rise to human gametes - After germ cell finishes meiosis, (23) chromosomes will end up in those gametes, giving it a haploid number (n) As in mitosis, duplicates DNA in interphase and (2) DNA molecules and associated proteins stay attached at centromere, deeming them sister chromatids. Also similarly to mitosis, microtubules of spindle apparatus move chromosomes in prescribed directions.
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