Cell Reproduction

Mitosis and Meiosis

Cell Reproduction Chromosome Structure

Individual chromosomes consist of 2 identical halves called CHROMATIDS

The center of the chromosome is the CENTROMERE. It holds the 2 chromatids together.

Chromosome

There are 2 types of chromosomes

SEX CHROMOSOMES-determine the sex of an organism In humans, sex chromosomes are either

X or Y FEMALES=XX MALES=XY

Types of chromosomes, cont.

AUTOSOMES-all other chromosomes Humans have 46 chromosomes total

44 autosomes, 2 sex chromosomes Organisms get 1 copy of each autosome

from a parent-making 2 copies called HOMOLOGOUS CHROMOSOMES. They are the same size, shape, and carry the same info.

VERY IMPORTANT VOCAB!!

Cells that have 2 sets of chromosomes are DIPLOID (2n).

HAPLOID (n) cells have only 1 set of chromosomes. Sperm and egg cells are haploid cells.

A KARYOTOPE is used to examine an individual’s

chromosomes.

Ticket to Leave What are the 2 parts of the

chromosome? What are the two types of

chromosomes in your body? Cells that have one set of

chromosomes are ______________. Cells that have two sets are ______________.

Cell Division in Prokaryotes

Divide asexually by BINARY FISSION Produce identical offspring 3 stages

DNA is copied Cell begins to divide 2 identical haploid cells are formed

Cell Division in Eukaryotes

MITOSIS Division of all other

cells Produces 2 new

identical cells, identical to the original cell

MEIOSIS Division of the sex

cells – sperm & egg

Produces 4 new similar cells, similar to the original cell

Cell Division in Eukaryotes

The CELL CYCLE is the repeating set of events that make up the life of a cell. CELL DIVISION is one phase and INTERPHASE is the time between divisions.

Interphase Made of 3 phases

G1 PHASE-offspring cells grow to mature size

S PHASE-DNA is copied (REPLICATION)

G2 PHASE-cell prepares for division

*Cells can exit the cell cycle and enter the G0 PHASE where DNA isn’t copied and cells don’t divide. Nervous system

cells stop dividing at maturity.*

Mitosis During mitosis, the M PHASE,

the nucleus of the cell divides. 4 phases of mitosis (Interphase

is before and after mitosis/cytokinesis.)PROPHASEMETAPHASEANAPHASETELOPHASE

PROPHASE DNA coils into

chromosomes Nucleolus and

nuclear membrane disappear

Dark spots appear (CENTROSOMES), which contain the CENTRIOLES (plants DO NOT have centrioles)

SPINDLE FIBERS radiate from the centrosomes

METAPHASEChromosome

s move to the MIDDLE of the cell

ANAPHASEChromatids

of each chromosome separate at centromere & move toward opposite sides of the dividing cell

TELOPHASE Spindle fibers

disappear Chromosomes

uncoil Nuclear membrane

forms around each set of chromosomes

Nucleolus reforms Telophase is

almost the opposite of prophase.

CYTOKINESIS CYTOKINESIS occurs when the

cytoplasm starts to divide. It starts when telophase is complete. In animal cells, the cell membrane

pinches in (CLEAVAGE FURROW) & separates the dividing cell into 2 new cells.

In plant cells, the membrane bound cell wall forms (CELL PLATE) & separates the cell into 2 new cells.

Cytokinesis in animal cells

Cytokinesis in plant cells

Ticket to Leave How does cell reproduction occur in

prokaryotes? What is the cell cycle? List and briefly describe the four

steps of mitosis.

Meiosis Cell division in SEX cells Produces haploid (n) reproductive

cells called GAMETES Human gametes are SPERM &

EGG Each contain 23 chromosomes Fusion of sperm (n) & egg (n)

forms a ZYGOTE (2n) that contains 46 chromosomes

**Cells begin meiosis just like mitosis—it’s just that cells divide

TWICE in meiosis**

Meiosis I

Meiosis II

DNA REPLICATIONDuring replication, the DNA

of a 2n (diploid) cell is copied.

This only occurs before MEIOSIS I.

Meiosis I PROPHASE I DNA coils, spindle fibers appear HOMOLOGOUS CHROMOSOMES

pair up-called SYNAPSIS (doesn’t happen during mitosis)

Portions of chromatids break off and attach to nearby chromatid on the homologous pair-called CROSSING OVERAllows for genetic info exchange between mother/father chromosomes giving a new mixture of genetic info-called GENETIC RECOMBINATION

CROSSING OVER

METAPHASE I TETRADS (each pair of homologous

chromosomes) line up in middle of cell

Spindle fibers attach to the homologous chromosomes of the pair

ANAPHASE I Each homologous chromosome

moves to the opposite side of the dividing cell

Random separation of the homologous chromosomes is called INDEPENDENT ASSORTMENT and it results in genetic variations

TELOPHASE I Chromosomes reach the opposite

ends of cell Each of the new developing cells will

contain a haploid number of chromosomes.

CYTOKINESIS I occurs

MEIOSIS II The newly formed cells DO NOT

copy their DNA. PROPHASE II

Spindle fibers form and move chromosomes toward the middle of the cell

METAPHASE II Chromosomes move to the midline of

the cells-facing opposite side of the cells

ANAPHASE II Chromatids separate and move to

opposite sides of cell

TELOPHASE II Nuclear membrane forms around

chromosomes in each of the 4 new cells

CYTOKINESIS II occurs resulting in 4 new cells, each containing HALF the number of chromosomes as the original cell

Ticket to Leave What is crossing over? Meiosis is used to form __________. List the steps of meiosis I & II. The formation of sperm is called

___________. The formation of eggs is called

__________.