Cell Cycle, Mitosis and Cell Division

• The lesson will cover cycles and patterns in living systems

Cell Cycle

• The cell cycle represents the life cycle of a cell
• It involves continuous cell growth and protein production
• DNA and centrosome duplication is part of the cell cycle
• Cytoplasmic materials are doubled

Cell Division

• Cell division involves karyokinesis and cytokinesis
• Cell division functions in reproduction, growth, and repair

Karyokinesis

• Karyokinesis means "karyo" (nucleus) and "kinesis" (movement)
• It involves the division of the cell nucleus

Cytokinesis

• Cytokinesis means "cyto" (cell) and "kinesis" (movement)
• It involves the division of the cell's cytoplasm
• Cleavage furrow occurs in animal cells
• Cell plate formation occurs in plant cells

Mitosis

• Mitosis is cell division that results in two identical cells
• It involves one division
• Daughter cells are diploid (2n)
• It occurs in somatic/body cells

Stages of Mitosis

• The stages of mitosis are prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis
• During interphase, the cell checks for complete DNA replication
• During early prophase, chromosomes condense and become visible, while the spindle forms as centrosomes move to opposite poles
• During prometaphase, the nuclear envelope breaks up and spindle fibers attach to kinetochores on chromosomes
• During metaphase, chromosomes line up along the equator of the cell
• During anaphase, centromeres split as sister chromatids separate and move to opposite poles
• During telophase, nuclear envelopes and nucleoli form at each pole and chromosomes decondense
• Cytokinesis divides the cytoplasm into two cells

Meiosis

• Meiosis involves two divisions: reductional and equational
• It results in four varied cells
• Daughter cells are haploid (n)
• Meiosis occurs in gametes (germ cells)

Meiosis I

• In prophase I, chromosomes condense, crossing over occurs, the spindle forms, and the nuclear envelope breaks up
• In metaphase I, paired homologous chromosomes line up along the equator of the cell
• In anaphase I, homologous chromosomes separate to opposite poles of the cell, while sister chromatids remain joined
• In telophase I and cytokinesis, nuclear envelopes form around chromosomes, which may temporarily decondense, and the cell may divide into two

Meiosis II

• In prophase II, spindles form and nuclear envelopes break up
• In metaphase II, chromosomes line up along the equator of the cell
• In anaphase II, centromeres split as sister chromatids separate to opposite poles of the cell
• In telophase II and cytokinesis, nuclear envelopes assemble around daughter nuclei, chromosomes decondense, spindles disappear, and Cytokinesis divides cells.
• Four nonidentical haploid daughter cells (n = 2) are produced

Spermatogenesis

• Spermatogenesis is the process of sperm production

Oogenesis

• Oogenesis is the process of egg production

Chromosomal Disorders

• These disorders result from nondisjunction, or failure of chromosomes to separate properly during cell division, which leads to extra or missing chromosomes in gametes

Types of Aneuploidy Syndromes

• XXX results in tall stature and menstrual irregularities in females
• XXY (Klinefelter syndrome) results in variable symptoms, often including sexual underdevelopment in males
• XYY (Jacobs syndrome) results in tall stature and acne in males
• XO (Turner syndrome) results in short stature and sexual underdevelopment in females

Mitosis vs. Meiosis

• Mitosis involves one nuclear division, while meiosis involves two
• Synapsis and crossing over occur in meiosis but not in mitosis
• Centromeres separate during anaphase in mitosis, while they separate during anaphase II in meiosis
• Mitosis results in two diploid daughter cells, while meiosis results in four haploid daughter cells
• Daughter cells in mitosis are genetically identical, while daughter cells in meiosis have genetic variation

Eukaryotic Reproductive Cycles

• There are three major reproductive cycles in eukaryotic organisms: haplontic, diplontic, and haplodiplontic

Haplontic Life Cycle

• The haplontic life cycle is also called zygotic meiosis
• The haploid (gametophytic) generation dominates over the diploid (sporophytic) generation
• The only diploid cell is the zygote
• Spores are haploid cells that can grow and be considered as fully functional organisms

Haplodiplontic Life Cycle

• Haplodiplontic cycle occurs in plants
• It is also called diplohaplontic
• It involves alternation of generations
• Sporophyte occurs in diploid and typically dominates in pteridophytes or ferns
• Gametophyte occurs in haploid and typically dominates in bryophytes or mosses

Diplontic Life Cycle

• Also called gametic meiosis
• Body or somatic cells of organism are diploid
• Zygote is diploid and grows by mitosis
• Key features are dominant sporophytic and diploid generation

Angiosperm Life Cycle

• Both gametophytes are reduced to a few cells.
• Antheridia & archegonia are lacking.
• Flowers are a key feature

Perfect Flower Structure

• Non-fertile parts include sepals and receptacle
• Fertile parts include male stamen and female carpel

Double Fertilization

• Double fertilization involves two sperm cells
• One sperm fertilizes the egg cell to form the zygote.
• The other sperm fuses with the two polar nuclei that form the endosperm

From Ovule to Seed

• The integuments develop into the seed coat.
• The central cell develops into the endosperm.
• The zygote develops into the embryo

Sexual Reproduction

• Asexual reproduction involves one parent that produces genetically identical offspring (unless mutation occurs)
• Sexual reproduction involves two parents that produce genetically variable offspring with mixed traits

Asexual vs. Sexual Reproduction

• Asexual reproduction is an efficient way to reproduce, allowing organisms to thrive without sex in stable ecosystems
• Harmful mutations tend to arise more often in asexual reproducers
• Sexual reproduction has widespread occurrence and provide advantage to adaptability, evolutionary flexibility, genetic diversity, take out harmful mutations

Types of Asexual Reproduction: Budding

• A new, duplicate plant or animal begins to form at the side of the parent and enlarges until an individual is created
• Parent and daughter cell or cells differ markedly in size
• Very common in plants (e.g., potatoes, onions, cacti) and in other organisms (i.e. yeasts, sponges, cnidarians)

Types of Asexual Reproduction: Regeneration

• Ability to restore lost or damaged tissues, organs or limbs
• Organism breaks into several pieces, each piece may regenerate the missing
• Occurs among invertebrates (i.e. worms and sea stars)

Types of Asexual Reproduction: Fission

• A type of cell division where one organism becomes two complete organisms
• The two new organisms have identical size and content of nuclei
• Common among bacteria, protozoans (e.g. paramecium), flatworms (i.e., planaria)

Types of Asexual Reproduction: Parthenogenesis

• An unfertilized egg develops into an adult animal
• Common among some mollusks, crustaceans, rotifers, some insects (wasps and honeybees), & some reptiles

Types of Asexual Reproduction: Vegetative Propagation

• Asexual plant propagation methods that produce new plants from vegetative parts of the original plant, such as the leaves, stems and roots
• New plants contain the genetic material of only one parent (clones of the parent plant)

Monoecious Reproduction

• Hermaphroditic, both male and female gonads can be found in only one organism
• Common among many invertebrates (i.e. earthworm, flatworm, leech)
• Perfect flowers have both male and female parts

Dioecious Reproduction

• Evolved from hermaphroditism
• Sexes are separate and labor is divided among the two sexes
• Flowers in plants are either male or female

Gender Bending

• Protandrous species develop first as males but could become females
• In protogyny, an individual is first a female, then could become a male

Courtship

• Visual and ritual displays because of 'choosy' females