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Results of fission
Mother cell goes into two identical daughter cells
What is F pilus?
Bridge between bacteria
Population of genetically identical cells
Visible mass of cells
Cells not actively replicating
Synthesis and replication
Generation of new cell
2 identical diploid (2n) cells
Produces 4 non identical haploid (n) cells
Where crossing over occurs.. then they will move down and more will cross at a different spot.
Touching point where exchange was made � only in meiosis
Sexual reproduction � carried out twice to get daughter cells with half of the info
- In both prokaryotic and eukaryotic cells, the genetic material is organized into
The Cellular Environment
- � Cytoplasm�the inside of a cell
- � Water
- � Hydrophilic and Hydrophobic Molecules
- � Carbohydrates
- � Lipids
- � Proteins, including enzymes
- � Membrane�made of lipids and proteins
- � Organelles
Double-stranded DNA with associated proteins and sometimes RNA
Prokaryotic cells contain what kind of chromosomes?
one circular chromosome plus smaller plasmids
Most eukaryotic cells contain what kind of chromosomes?
several large linear chromosomes
Cell Division in Prokaryotes: Fission
- A mother cell divides to produce two daughter cells.
- The mother cell�s chromosome is duplicated prior to fission.
- Each daughter cell receives one copy of the chromosome.
a population of genetically identical cells.
a visible mass of cells.
Cells, the basic units of all living things, are enclosed by
Chromosomes, the cellular structures that carry the genes, are composed of
DNA, RNA, and protein.
In eukaryotes, chromosomes are contained within a membrane-bounded nucleus;
in prokaryotes they are not.
Eukaryotic cells possess complex systems of internal membranes as well as membranous organelles such as
mitochondria, chloroplasts, and the endoplasmic reticulum.
When eukaryotic cells divide, they distribute their genetic material equally and exactly to their offspring.
Components of mitosis:
- � Microtubules and Centrioles
- � Spindle
- � Microtubule organizing centers (MTOCs)
- � Centrosomes and centrioles
- � Pericentriolar material
- � Aster
As a cell enters mitosis, its duplicated chromosomes
condense into rod-shaped bodies (prophase).
As mitosis progresses, the chromosomes migrate to the
equatorial plane of the cell (metaphase).
Later in mitosis, the centromere that holds the sister chromatids of a duplicated chromosome together splits, and the sisters chromatids
separate (or disjoin) from each other (anaphase)
As mitosis comes to an end, the chromosomes
decondense and a nuclear membrane reforms around them (telophase).
Each daughter cell produced by mitosis and cytokinesis has the same set of chromosomes; thus, daughter cells are genetically identical.
Sexual reproduction involves a mechanism that reduces the number of chromosomes by half.
Prophase I: Leptonema
- � Chromosomes condense
- � Each chromosome has two sister chromatids
Prophase I: Zygonema
- � Synapsis of homologous chromosomes
- � Synaptonemal complex
Prophase I: Pachynema
- � Chromosomes condense further
- � Bivalent
- � Tetrad
- � Crossing over occurs
Prophase I: Diplonema
� Paired chromosomes separate slightly but are in contact as chiasmata
Prophase I: Diakinesis
- � Nuclear envelope fragements
- � Spindle fibers attach to kinetochores
- � Chromosomes move to central plane in pairs
- � Paired chromosomes are oriented toward opposite poles
- � Terminalization: chiasmata move toward telomeres
- � Chromosome disjunction (separation of paired chromosomes)
- � Separated homologues move toward opposite poles
- � Chromosomes reach the poles; nuclei forms
- � Spindle apparatus is disassembled
- � Daughter cells separated by membranes
- � Chromosomes decondense
- � Each chromosome still has two sister chromatids
- � Chromosomes condense
- � Chromosomes attach to a new spindle apparatus
- � Sister chromatids are attached to spindle fibers from opposite poles
� Chromosomes align at equatorial plane
- � Centromeres split
- � Chromatid disjunction�sister chromatids move toward opposite poles
- � Separated chromatids gather at poles; daughter nuclei form
- � Each chromatid is now called a chromosome
- � Each daughter nucleus contains a haploid set of chromosomes
Outcome of meiosis?
- � Daughter cells are NOT genetically identical
- � Maternal and paternal homologues synapse, then disjoin. Different pairs disjoin independently.
- � Homologous chromosomes exchange material by crossing over
Diploid eukaryotic cells form haploid cells by
meiosis, a process involving one round of chromosome duplication followed by two cell divisions (meiosis I and meiosis II).
During meiosis I,
homologous chromosomes pair (synapse), exchange material (cross over), and separate (disjoin) from each other.
During meiosis II,
chromatids disjoin from each other.
In many organisms, the haploid products of meiosis develop directly into
In plants, the products of meiosis divide mitotically to form haploid
The gametophytic phase of a plant�s life cycle alternates with the sporophytic phase, which is diploid; meiosis occurs in the sporophyte.
Genetics in the Laboratory: An Introduction to Some Model Research Organisms
Geneticists focus their research on microorganisms, plants, and animals well suited to experimentation.
Eschericia coli,a Bacterium
- � ?Rod-shaped bacterium
- � ?Molecular Genetics
- � ?4.6 ?106base pairs
- � ?4288 protein-coding genes
- � ?Single circular chromosome
- � ?Bacteriophages
Saccharomyces cerevisiae,Baker�s Yeast
- � ?Unicellular fungus
- � ?16 linear chromosomes
- � ?12 ?106base pairs
- � ?6268 genes
- � ?Reproduces sexually and asexually
Drosophila melanogaster,a Fruit Fly
- � ?Insect
- � ?Anatomically complex
- � ?170 ?106base pairs
- � ?13,792 genes
Caenorhabditis elegans,a Round Worm
- � ?Model for animal development
- � ?Hermaphroditic
- � ?100 ?106base pairs
- � ?20,512 genes
Mus musculus,the Mouse
- � ?Biomedical research
- � ?Comparative genomics
- � ?2.9 ?109base pairs
- � ?25,396 genes
Danio rerio,the Zebrafish
- � ?Model for vertebrate development
- � ?Transparent eggs; external fertilization
- � ?1.6 ?109base pairs
- � ?23,524 genes
Arabidopsis thaliana,a Fast-growing Plant
- � ?Self-fertilizing
- � ?Model for agriculturally significant plants
- � ?157?106base pairs
- � ?27,706 genes
Homo sapiens,Our Own Species
- � ?Cell culture
- � ?DNA Cloning
- � ?The Human Genome Project
- � ?3.2 ?109base pairs
- � ?20,000 to 25,000 genes
The bacterium E. coliis the premier prokaryote for
Model eukaryotes include
yeast (S. cerevisiae), a fruit fly (D. melanogaster), a round worm (C. elegans), the mouse (M. musculus), the zebrafish (D. rerio), and a fast-growing plant (A. thaliana).
Techniques such as ____ and _____have made it possible to study the genetic material of human beings and many other organisms.
cell culture and DNA cloning