mitosis-meiosis-1

The segregation of genes for different characters is

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Unformatted text preview: erent characters is 4) independent for each character. independent Mitosis & Meiosis Phases of mitosis The cell cycle Meiosis gamete formation Haploid - Diploid life cycles Chromosomal theory of genetics Mendel's Principles: Mendel's Principles: Mendel's 1) Traits are inherited as genes, invisible , 1) Traits are inherited as genes, invisible , indivisible, charact ers passed from one indivisible, charact ers passed from one generation to th e next. generation to th e next. 2) Some genes are domina nt over others. 2) Some genes are domina nt over others. 3) During gamete formatio n, the two copies o f a 3) During gamete formatio n, the two copies o f a gene are segregat ed from each other gene are segregat ed from each other 4) The segregat ion of genes for dif ferent 4) The segregat ion of genes for dif ferent characters is indep endent for each c haracter. characters is indep endent for each c haracter. Next: Next: WHERE are the genes? Are they real? Are they somewhere in the cell? Are (If they were, they’d have to be carefully duplicated and doled out to daughter cells after cell division. And, segregated during gamete formation) http://www.mendel-museum.org/ http://www.mendel-museum.org Mitosis in cultured newt lung cell Interphase (cell not in mitosis) Interphase (cell Prophase (chromosomes condense) (chromosomes Metaphase (chromosomes aligned) (chromosome movement) Anaphase Anaphase (nuclei reorganize) Telophase Telophase Mitotic Spindle formation involves major rearrangements of cellular structures Microtubules (tubulin) Chromosomes (DNA) Kinetochores (CENP-A) Mitosis is just one Mitosis is just one phase in a Cell Cycle phase in a Cell Cycle with four major with four major phases: phases: Progression through the Progression through the Cell cycle is regulated at Cell cycle is regulated at aa series of “checkpoints.” series of “checkpoints.” ••Control of the cell cycle Control of the cell cycle by proteins known as by proteins known as cyclins and cyclincyclins and cyclindependent protein kinases dependent protein kinases ((CDKs)is a major topic in CDKs) is a major topic in Bio 500 and Bio 1050 -Bio 500 and Bio 1050 upper level Cell Biology upper level Cell Biology courses. courses. Haploid Haploid Gametes Diploid Zygote Here’s where Segregation takes place! ••Meiosis consists Meiosis consists (usually) of two stages (usually) of two stages (Meiosis I Iand Meiosis II) (Meiosis and Meiosis II) ••Meiosis I Ikey event: Meiosis key event: Pairing of homologous Pairing of homologous chromosomes in chromosomes in prophase & metaphase prophase & metaphase offMeiosis I. o Meiosis I. ••MeiosisII key event: a Meiosis II key event: a second round of second round of division not preceded by division not preceded by an S phase (no an S phase (no chromosome chromosome duplication) duplication) Meiosis I Meiosis Meiosis II Here’s where Independent Assortment takes place! Freeman 4/e Fig. 12/8 [3e, Figure 12.5] Insight -- Chromosomes, not genes, Insight Chromosomes, not genes, assort independently! assort independently! A “Chromosomal” Theory of Inheritance 1) chromosome is the physical vehicle by which genes are transmitted from one generation to the next generation 2) genes are arranged on chromosomes in a 2) linear sequence linear 3) Diploid cells have two sets of homologous 3) chromosomes chromosomes 4) Each homologue pairs with its partner at 4) meiosis meiosis 5) The assortment of chromosomes is 5) independent independent Two homologous Chromosomes Two A gene LOCUS, with gene LOCUS with identical alleles alleles A gene LOCUS, with gene LOCUS with different alleles alleles An ALLELE is a particular An form of a gene. Example: The gene for pea flower color comes in two alleles — pink and white alleles Non-disjunction (failure to separate) in meiosis may produce diploid (2n) gametes. may Since many plants can self-fertilize, this may Since result in a tetraploid (4n) organism = instant speciation! speciation! Tetraploid Iris “polyploid” = having more than the diploid (2n) number of chromosomes number...
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