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Download Chromosomal basis of inheritance cell division – mitosis and meiosis
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Transcript
Chromosomal basis of inheritance cell division – mitosis and meiosis double helix DNA is normally dispersed in cell; condensed prior to cell division nucleosomes ‘supercoil’ chromosome (metaphase) Location of DNA in cells: Chromosomes structure: two chromatids connected at the centromere Chromosomes • each species has a characteristic set of chromosomes • individual chromosomes vary in size and shape • number and size is unrelated to complexity of organism karyotype Mitosis – cell replication interphase prophase metaphase anaphase telophase Mitosis – cell replication interphase: DNA replication occurs to produce double-chromatid chromosomes prophase: DNA condenses metaphase: chromosomes align in center of cell anaphase: chromatids separate, move toward opposite poles telophase: nuclear membranes reform; cell splits into two (cytokinesis) Meiosis – cell division with chromosome # reduction reductional division interphase prophase I metaphase I equational division anaphase I metaphase II anaphase II telophase II Meiosis – cell division with chromosome # reduction crossing-over Segregation of chromosomes Meiosis I Meiosis II Oogenesis vs. spermatogenesis sperm – many, with small cellular investment mitochondria rarely transferred to zygote ova – few, with large cellular investment many mitochondria inherited Oogenesis vs. spermatogenesis sperm – many, with small cellular investment mitochondria rarely transferred to zygote ova – few, with large cellular investment many mitochondria inherited (remember mitochondrial DNA?) polar bodies (3) Chromosomes • each species has a characteristic set of chromosomes N = number of unique chromosomes (haploid number) 2N = number of chromosomes in somatic cells of diploid species • number and size of chromosomes is unrelated to complexity of organism (e.g., nematode N varies from 1 to 48)