Transcript Cell Division Teacher Notes

DNA in the Cell
Inside the nucleus are chromosomes, which house
DNA
Chromosome made from proteins + histones. Coils
DNA so it can fit into a cell
Each chromosome consists of identical halves called
chromatids
Center of the chromosome is called the centromere
Number & Types of
Chromosomes
Sex chromosomes determine the sex of an organism
XX = female
XY = Male
All other chromosomes are called autosomes
Homologous Chromosomes
Each organism gets two copies of each autosome; 1 from mom and 1 from
dad (46 total chromosomes; 23 pairs in humans)
Each 2 paired chromosomes are called homologous chromosomes
Homologous chromosomes carry genes for the same traits
Homologous Chromosomes
How Many Chromosomes?
CARP- 104
ELEPHANT-56
KANGAROO-12
PINEAPPLE-50
SHRIMP-92
ADDER’S TONGUE FERN-1200
Diploid & Haploid Cells
Diploid Cells  Cells with 2 copies of each chromosome
Haploid Cells  Cells with 1 copy of each chromosome
Most cells in the body are diploid
Sex cells (sperm & egg) are haploid
Diploid & Haploid Cells
Why Do Cells Divide?
1. Get too big (take in more nutrients than they can metabolize)
2. Death/ Need replacement
3. Surface to volume ratio; too much volume, not enough surface
When do cells divide?
Depends on the type of cell (days, weeks, months, some never divide)
Cell Cycle  Cells will grow, replicate, and die
Cell Division in Prokaryotes
Prokaryote  unicellular bacteria with no nucleus
Binary Fission  DNA is replicated, cell doubles in size
and splits
Stages of Cell Cycle in
Eukaryotes
Interphase  Growth Phase
G1  Cell growth
S  Synthesis/ Replication of DNA
G2 -> Final growth
Mitosis  DNA, which has
been replicated (remember last unit?)
needs to be distributed equally
to each new cell
Stages of Mitosis
Prophase
Chromatin condenses (chromosomes) & nucleus disappears
Spindle fibers (microtubules) form & move chromosomes
Metaphase
Spindles align chromosomes in the middle of the cell
Anaphase
Centromeres divide and sister chromatids split
Chromatids move toward opposite poles
Telophase
Chromosomes arrive at opposite ends of cell
Nucleus reappears
Spindle disappears
Cell splits (cytokinesis)
Stages of Mitosis
Cytokinesis
Animal Cell  cleavage furrow pinches one cell into 2
cells
Plant Cell  cell plate makes new cell wall; cell splits
Mitosis Animation
Additional Mitosis
Vocabulary
G0 Phase  Cell is neither growing or dividing
Centrioles Create Ropes that pull chromosomes
around the cell (make
spindle fibers)
Difference Between Plant
Cell & Animal Cell Mitosis
•Plant cells are surrounded by a tough outer case
called a cell wall
•Animal cells are surrounded by a soft outer case called
a cell membrane
•The first 3 stages of mitosis in plant and animal cells
are the same
Telophase
Animal Cell  Formation of a cleavage furrow
Plant Cell  Formation of cell plate
Meiosis Vocabulary
•Diploid Cells  cells with 2 of each type of chromosome (1 from mom
and 1 from dad)
•n= number of pairs of chromosomes
•Diploid Cells = 2n
•Zygote = fertilized egg
•Gametes= haploid sex cells
•Fertilization= union of egg and sperm
•Sexual Reproduction  Parents generate specialized sex cells
Meiosis
Getting from diploid to haploid cells: Meiosis
Where does it occur in humans?
Males Testes
Females  Ovaries
Meiosis Overview
Meiosis I
Diploid cells splits into 2 haploid cells
Meiosis II
2 haploid daughter cells undergo mitosis
Forms 4 haploid sex cells
Same as mitosis
Meiosis I
Prophase I
Homologous chromosomes pair together (called synapsis)
Each homologous pair of chromosomes is called a tetrad
Some chromatids break off and attach to adjacent homologous chromatids
(crossing over)
Crossing Over creates new genetic combinations
Metaphase I
Homologous chromosomes line up in the middle of the cell
Anaphase I
Homologous CHROMOSOMES move to opposite poles of the cell
Random separation of homologous chromosomes is called Independent
Assortment
Telophase I
Chromosomes reach opposite poles of the cell
Cytokinesis begins
Meiosis I
Meiosis II
2 haploid cells go through the process of mitosis & cell
division
End result of meiosis II is 4 haploid cells
Gamete Formation
In males meiosis creates 4 sperm cells (called
spermatids)
In females the cytoplasm is unevenly divided so that
only 1 big cell is formed, along with 3 other polar
bodies
Meiosis II
Meiosis Animation
Meiosis Animation