BIOL 152 1st Edition Lecture 6 Outline of Last Lecture - Origins and Molecular Basis of Genetics Outline of Current Lecture The Cell CycleMitosis - two daughter cellsMeiosis - four genetically different cells going from diploid to haploid Cellular organization of genetic material- Genome- Chromosomeso 46 in human somatic cells (23 pair) o 23 in gameteso Chromatin = DNA + protein o Sister chromatidso CentromeresThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Cell division occurs within a cycle of cell activityInterphase:o G1o So G2 The Process of MitosisThe stages of mitosis:- Interphase- Prophase- Prometaphase- Metaphase- Anaphase- Telophase - CytokinesisThe Mitotic Spindle- Forms between 2 centrosomes- Microtubules stretch outward from centrosomeo Hollow tubes of protein - Kinetochore - protein in centromere where microtubules attach The Mitotic Division of an Animal CellG2 of Interphase- Centrosomes replicate- Nuclear envelope still intact - Chromosomes duplicated (S phase) but not condensedProphase- Chromatin condenses, forms sister chromatids- Mitotic spindle forms- Centrosomes move to opposite ends of cell- Kinetochores developPrometaphase- Nuclear envelope fragments- Microtubules extend towards kinetochores- Non-attached microtubules interact with opposite microtubulesMetaphase- Chromosomes converge on “metaphase plate”- Each chromatid pair has kinetochore attached to microtubules – cell cycle check point- Enzyme unravels DNA strands at centromeresAnaphase- Sister chromatids separate- Chromosomes move via motor protienso 2 hypotheses for how motor proteins move1. Pacman type movement where protein gnaws on microtubules to 2. Reeling in when proteins are pulled in by microtubules - Cell elongates as non-attached microtubules lengthenTelophase- Nuclear envelope reforms- Chromosomes become less condensedCytokinesis- In animals, cleavage furrow pinches cello Actin and myosin filaments contract- In plants, cell plate is laid down and cell wall formsMeiosis and Sexual Life CyclesSexual versus Asexual ReproductionSexual requires two mates of different sex, asexual is an organism able to reproduce by itself (fission or cell replication)In human somatic cells there are:- 46 chromosomes, 23 homologous pairs- Autosomes and Sex chromosomeso XX for females and XY for malesKaryotype - process of staining chromosomes to view the number and genetic factors of the autosome and sex chromosomesOverview of MeiosisHaploid versus Diploid Prophase I- Nuclear envelope breaks down, centrosomes move to poles, spindle microtubules form, and chromosomes begin to condense- Homologous pair chromosomes pair up- Synapsis forms, where pairs of chromosomes attach themselves firmly - Crossing over occurs, site of occurrence is known as chiasmataMetaphase I- Homologous pairs line up on metaphase plate; one chromosome from each pair facing each pole- Kinetochore microtubules attached to each homologous pairAnaphase I- Homologous chromosomes, composed of two sister chromatids move to opposite polesTelophase I and Cytokinesis- Each half of cell is haploid, but each chromosome still composed of two sister chromatids - Cytokinesis (division of the cytoplasm) occurs simultaneously- In some species, the chromosomes de-condense and the nuclear envelope reforms- No replication occurs between Meiosis I and IIProphase II- Spindle apparatus formsMetaphase II- Because of crossover, the two sister chromatids are not genetically identical- Kinetochores from sister chromatids are attached to microtubules and they line up on the metaphase plateAnaphase II- Centromeres of each chromosome come apart and sister chromatids separateTelophase II and Cytokinesis- Nuclei form- Chromosomes decondense- All four haploid daughter cells are distinct from each other and their parent cellsComparison of Meiosis and Mitosis- Chromosome number- Genetic variationThree Mechanisms for Genetic Variation1. Independent Assortment – random orientation of homologous pairs on the metaphase plate (223 possibilities)2. Crossing over – DNA molecules of two non-sister chromatids are broken at the same place and rejoined to each other’s DNA3. Random FertilizationHeritable variation is what makes evolution