Chapter 16 Cellular Reproduction

Chromatin

Unpackaged stage of chromosomes during interphase.

Chromatids

Half of a replicated chromosome

Chromosomes

Linear package of DNA containing genes

Unreplicated: One piece of DNA before s-phase

Replicated: Two pieces of DNA after s-phase

Centromere

Protein Structure connecting sister chromatids on a replicated chromosome

Spindle Fibres

Microtubules strands that separate chromosomes during cell division

• Synthesized by centrioles in a spindle aparratus

• Attach to a protein on the centromere

Ploidy

Chromosome Number

Diploid

Two of each chromosome ex:2n

Haploid

One of each chromosome ex: 1n

Polyploid

Multiple copies of each chromosome (Xn)- some plants are triploid or tetraploid

The Eukaryotic Cell Cycle

Interphase: Business as usual; largest stage of the cell cycle; involves growth and metabolic activity in three phases

Cell Division

Mitosis and split of DNA

• prophase, metaphase, anaphase, telophase

• Cytokinesis (split cytoplasm and organelles)

Karyotype

A Way to See Chromosome Number

Interphase

Growth 1 (G1) phase: cell growth & differentiation

(G0: non-dividing e.g. nerve cells)

b) Synthesis (S) phase: synthesis of DNA =chromosome replication

c) Growth 2 (G2) phase: more cell growth!

Cell Division

Mitosis (split DNA & nuclei)

Prophase (Prepare!)

Nuclear membrane &

nucleolus disappearReplicated chromosomes condense from chromatin spindle fibres form from

centrioles & attach to centromeres

Metaphase (“Meet/Middle”)

Spindle fiber “tug-of-war” causes the replicated chromosomes to line up along the equator

Anaphase (“Apart/Away”)

Replicated chromosomes are pulled apart Sister chromatids from each chromosome are pulled to the poles of the cell & become unreplicated chromosomes

Telophase (“End…Tada!”)

Spindle fibers disappear

Nucleus membrane reappear, Cleavage form Unreplicated chromosomes relax into chromatin

Cytokinesis:

microfilaments wrap around cell waist, pinching off two daughter cells by dividing the cytoplasm

Diploid daughter cells (G1)

Genetically identical to parent cell

Cells are now in G1 phase of interphase

Interphase-1

Occurs before meiosis Same as mitosis

Regular metabolic activities Growth & differentiation

Replicated chromosomes in chromatin form

Meiosis I - Prophase I

Nuclear membrane & nucleolus disappear

Chromatin condenses into tight chromosomes

Spindle fibers extend from centrioles and attach to centromeres

Synapsis: 46 homologous chromosomes pair up 🡪 form 23

tetrads

Tetrad: two replicated homologous chromosomes linked by protein filaments

Metaphase I

Spindle fiber “tug-of-war” causes tetrads to line up along

equator

independent assortment: maternal and paternal

chromosomes randomly line upon either side of the equator 🡪

genetic variation

Anaphase 1

Segregation: tetrads separate and replicated chromosomes are

pulled to poles

Telophase I

Spindle fibers disappear Nuclear membrane (but not

• nucleolus) reappears Chromosomes may relax, but

don’t fully unwind into chromatin

• Cleavage furrow forms

• Cytokinesis divides cytoplasm

Meiosis II – Prophase II

• Nuclear membranedisappears

• Chromosomes fully condense

• Spindle fibers form from

• centrioles and attach to centromeres

Metaphase II

Spindle fiber “tug-of-war” causes replicated chromosomes to line up along the cell equator

Anaphase II

Replicated chromosomes are pulled apart

Sister chromatids from each chromosome pulled to the poles

of the cell & become unreplicated chromosomes

Telophase II

• Spindle fibers disappear

• Nuclear membrane & nucleolus reappear

• Unreplicated chromosomes relax into chromatin

• Cleavage furrow forms

Cytokinesis divides thecytoplasm

Haploid Daughter Cells

• Daughter cells are sperm or eggs,

they are not in interphase of a regular cell cycle

• daughter cells are haploid

  (1n=23 chromosomes)

Trisomy

an extra chromosome or part of a chromosome

e.g. trisomy 21 🡪 Down’s Syndrome

Monosomy

missing an entire chromosome/part of a chromosome

e.g. XO 🡪 Turner Syndrome

Budding

Complete (but miniature) version of the parent grows out from parent’s body (e.g.: yeast, Hydra)

• New organism separates to become an independent

Vegetative Reproduction

• Similar to budding but in plants Example: Strawberry plants

• Plants spread across a garden by extending thin stems

• A new plant develops at the end of each stem, takes root and

separates from original

Fragmentation

• Creation of new plants from a fragment (portion) of a parent

plant Example: Potatoes!

• Entire plants are grown from a fragment (tuber) of a parent

plant Using “cuttings”

Parthenogenesis

• Many animals are capable of some forms of asexual reproduction

SEA STARS can reproduce by fragmentation! Others through parthenogenesis…

• Unfertilized egg develops into an adult!

Examples include some lizards, some fish, and bees!