Mitosis Meiosis 1

7/25/2019 Mitosis Meiosis 1

1/44

Mitosis and MeiosisCell Division


2/44

Why Do Cells Divide?

For growth, repair, and

reproduction


3/44

Mitosis

Organisms grow by theadditionof cells

In multicellular organismsome of these cells

perform functions dierentfrom other cells.


4/44

he process of a cellbecoming dierent is

diferentiation. !nder normal conditionsonce an animal cell becomes

speciali"ed it can nolongerform an entire organism,however plant cells are

totipotent and any cell canform an entire plant.


5/44

When do cells divide?

Most limiting factor in si"e isthe si"e of the cell membrane.Cells must obtain nutrients

as volume increases, cellsurface area does not increaseas greatly

larger cells re#uire a largersurface area for survival


6/44

Cell Division vs. $uclearDivision

Cyto%inesis& he actual division of thecell into two new cells.

Mitosis& he division of the nucleus ofthe cell into two new nuclei.

$ote& 'ometimes cells go throughmitosis without going throughcyto%inesis. Describe a cell that did this.


7/44

erminology

Chromatin( thin )brousform of D$* and proteins

Sister chromatids(identical structures that

result from chromosomereplication, formed during 'phase


8/44

*natomy of a

Chromosome Centromere(

point where sisterchromatids are

+oined together

Pshort arm-upward

Qlong arm-

downward

Telomere(tips ofchromosome

p -arm

centromere

q-arm

telomerechromatids


9/44


10/44

ow Do Cells Divide/

Cell cycle( se#uence ofphases in the life cycle of

the cell


11/44

Getting ready to split

Cell cycle has two parts:

growth and preparation

0interphase1cell division

mitosis 0nuclear division1cyto%inesis 0cytoplasm division1


12/44

Interphase

Occurs betweendivisions

2ongest part of cycle 3 stages


13/44


14/44

Interphase

45 or 4ap 5

he cell +ust )nisheddividing so in 4ap 5the cell is recovering

from mitosis


15/44

Interphase

' or 'ynthesis

stageD$* replicates


16/44

Interphase

4 6 or 4ap 6

his is preparationfor mitosis

Organelles are

replicated.More growthoccurs.


17/44


18/44

MITOSIS

Mitosis begins after G 2 and ends

before G 1


19/44

7rophase

Chromosome

condense Microtubles form

he nuclear

envelope brea%sdown


20/44

Metaphase

Chromosomes

are pulled tocenter of cell

2ine up along8metaphaseplate9


21/44


22/44

*naphase

Centromeres divide 'pindle )bers pullone set of

chromosomes toeach pole

7recise alignmentis critical todivision


23/44


24/44

elophase

$uclear envelope form aroundchromosomes

Chromosomes uncoil

Cyto%inesisanimals ( pinching of plasma

membrane

plants( elongates and the cell plateforms0 future cellwall and cellmembrane1


25/44

Meiosis


26/44

What is Meiosis?

A division of the nucleus that reduces

chromosome number by half.

Important in sexual reproduction

Involves combining the genetic

information of one parent with that of

the the other parent to produce a

genetically distinct individual


27/44

erminology

Diploid( two sets ofchromosomes 06n1, in

humans 63 pairs or :; total Haploid( one set of

chromosomes 0n1 ( gametesor se< cells, in humans 63chromosomes


28/44

Chromosome 7airing

Homologous pair

each chromosome in pair

are identical to the other0 carry genes for same trait1

only one pair diers ( se


29/44

7hases of Meiosis

* diploid cell replicates itschromosomes

wo stages of meiosis

Meiosis I and Meiosis II

Only 5 replication


30/44


31/44

Synapsis( pairing ofhomologous chromosomes

forming a tetrad.Crossing over( chromatidsof tetrad e


32/44

Meiosis I


33/44

7rophase I

Chromosomes condense

omologous chromosomes pair

w? each other @ach pair contains four sister

chromatids ( tetrad


34/44

Metaphase I

etrads or

homologouschromosomes move to

center ofcell


35/44

*naphase I

omologou

schromosomes pulled to

oppositepoles


36/44

elophase I

Daughter

nucleiformed

hese arehaploid 05n1


37/44

Meiosis II

Daughter cells undergo a

second division- muchli%e mitosis

NO ADDITIONA!"#ICATION OCC$!S


38/44

7rophase II

'pindle

)bers formagain


39/44

Metaphase II

'isterchromatidsmove to thecenter


40/44

*naphase II

Centromeressplit

Individualchromosome

s are pulledto poles


41/44

elophase II A

Cyto%inesis Four haploid

daughtercells resultsfrom one

originaldiploid cell

ev ew os s


42/44

ev ew os sMeiosis

oth are forms of nucleardivision

oth involve replication

oth involve disappearance ofthe nucleus, and nucleolus,

nuclear membrane oth involve formation ofspindle )bers

DI%%"!"NC"S


43/44

DI%%"!"NC"S &eiosisproduces daughter cells that

have 1/2the number of chromosomesas the parent. 4o from 6n to 5n.

Daughter cellsproduced by meiosis

are notgenetically identicalto oneanother.

In meiosiscell division ta%es placetwice but replication occurs onlyonce.


44/44

alue of ariation

'ariation( dierencesbetween members of apopulation.

Meiosis results in randomseparationof chromosomes ingametes.

Causes diverse populationsthat over time can be strongerfor survival.

Documents

Mitosis Meiosis 1