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Replicated Chromosomes – identical DNA on sister chromatids which are connected at the centromere

q-arm p-arm Replicated Chromosomes – identical DNA on sister chromatids which are connected at the centromere Unreplicated Chromosome Locus – physical location of a gene on a chromosome Ploidy level = # of versions of each chromosome Haploid = 1 version – bacteria, some male insects

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Replicated Chromosomes – identical DNA on sister chromatids which are connected at the centromere

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  1. q-arm p-arm Replicated Chromosomes – identical DNA on sister chromatids which are connected at the centromere Unreplicated Chromosome Locus– physical location of a gene on a chromosome

  2. Ploidy level = # of versions of each chromosome • Haploid = 1 version – bacteria, some male insects • Diploid = 2 versions – we are diploid; one version came from mom, one from dad • Polyploid = 3+ versions – many plant species

  3. A A A a b b b a a b b b Diploid species have homologous pairs of chromosomes each chromosome in the pair has the same genes, but different alleles Gene = region of DNA that codes for a specific protein Allele = a type, or version, of a gene Cell nucleus in G1 – unreplicated, homologous pairs heterozygous for Gene A (two different alleles), homozygous for gene B (same alleles) During S stage of Interphase, DNA is replicated Sister Chromatids Homologous Pair

  4. Chromosomes are located in the . . . . . Dr. G. Weaver, Colorado University at Denver

  5. The Science Creative Quarterly

  6. Mitosis begins with one diploid cell with replicated DNA Mitosis ends with two diploid cells with unreplicated DNA When is DNA replicated? How many total copies of each gene are there in metaphase?

  7. Meiosis begins with one diploid cell with duplicated DNA Meiosis ends with four haploid cells with unduplicated DNA How many total copies of each gene are there in Metaphase I? in Metaphase II?

  8. Purves et al., Life: The Science of Biology

  9. Crossing Over During Prophase I • Leptonema – chromatin begins condensing, search for homologs • Zygonema – condensation continues, rough pairing at telomeres (ends) • Pachynema – pairing all along chromosomes, chiasmata form, crossing over occurs in some places • Diplonema – some decondensation and separation outside of chiasmata, some proteins (like yolk) made – cells can stay in this stage for many years • Diakinesis – recondensation, chiasmata marginalized to telomeres so homologs don’t remain attached at centromeres Importance of crossing over is that no two gametes are identical!

  10. Haploid (n) Meiosis Fertilization Diploid (2n) Mitosis

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