CELL REPRODUCTION Chapter 8

•CHROMOSOMES•CELL DIVISION•MEIOSIS

WHAT IS DNA?

• Deoxyribonucleic acid• Long thin molecule

that stores genetic info

• In humans- 6 billion pairs of nucleotides

• If a cell were the size of a basketball, the DNA would stretch for 40 miles!

CHROMOSOME STRUCTURE

• DNA is coiled into very compact structures called chromosomes.

• CHROMOSOMES are rod-shaped structures of DNA + histone PROTEIN.

Replicated DNA

• Each half of the chromosome is called a CHROMATID.

(divide it vertically)• Identical chromatids

formed during S phase of the cell cycle ensure that cell division will result in indentical cells.

• They are connected at the CENTROMERE.

Draw and label this chromosome

CHROMOSOME NUMBER• Each species has a certain

number of chromosomes in each cell.

• For each chromosome there are two copies- one from Mom & one from Dad.

• For example, humans have 46 and gorillas have 48!

• Cats, like mine… Pele, have 32 of them!

HOMOLOGOUS Chromosomes

• Every cell of an organism produced by sexual reproduction has two copies of each autosome.

• Get one copy of each autosome from each parent.

• Two copies of each chromosome that contain the same genes are called HOMOLOGOUS.

KARYOTYPE photomicrograph of all the chromosomes in the

nucleus of a cell• AUTOSOMES are the

chromosomes besides the sex chromosomes- numbered 1-22.

• In humans, 44 chromosomes are AUTOSOMES and the other 2 are sex chromosomes.

• What sex chromosome combination do males have?

SEX chromosomes• Sex Chromosomes

determine the sex of an organism.

• In humans: XX is female

XY is male

* This is why males determine the sex of the baby!

Haploid & Diploid Cells• Haploid Cells (1n)

-have one of each chromosome-examples: sperm cells, egg cells

• Diploid Cells (2n)-have pairs of chromosomes-examples: all non-reproductive cells.

• Exception: red blood cells don’t have any chromosomes because they are missing a nucleus!

CELL DIVISION IN PROKARYOTES

Prokaryotes have ONE chromosome that exists as a loop. They also have no nuclear envelope separating their DNA

from the rest of the cell.BINARY FISSION is the division of a prokaryotic cell (bacteria) into two identical cells!

1. DNA copied2. Copies move3. Cell membrane begins

to divide the cell in two

4. Two identical haploid cells are formed.

CELL DIVISION IN EUKARYOTES

is more complicated because the DNA is enclosed in a nuclear envelope, the DNA is arranged in multiple strands, with a duplicate

copy of each chromosome.• NUCLEUS divides (karyokinesis) before the cell divides (cytokinesis)

Two types:1. MITOSIS (makes clones)

-reproduction of unicellular organisms-addition of cells to a tissue or organ.

2. MEIOSIS (makes gametes)-used for sexual reproduction-1/2 as many chromosomes-sperm & egg can recombine in sexual reproduction.

THE CELL CYCLEThe events that occur in the “life” of a cell. The cell grows and copies its’ DNA during Interphase (the longest phase),

then divides during M phase.• INTERPHASE

- G1 (growth)- S (DNA synthesis)- G2 (growth)

• MITOSIS-nuclear division- prophase- metaphase- anaphase- telophase

• CYTOKINESIS-cytoplasmic division

-cleavage furrow in animal cells - cell plate forms in plant cells.

Question: Where does the toy poodle urinate when it

is raining outside?

• THE PMAT

• Prophase• Metaphase• Anaphase• Telophase

MITOSIS & MEIOSIS

Chapter 8

MITOSISresults in identical cells.

Behavior of chromosomes in KARYOKINESIS is

simple: sister chromatids

separate

1. PROPHASE- replicated DNA condenses into replicated chromosomes (sister chromatids)

2. METAPHASE- replicated chromosomes line up on the metaphase plate (imaginary center plane of cell)

3. ANAPHASE- sister chromatids are pulled apart to opposite “poles” of the cell.

4. TELOPHASE- nuclear envelope reforms.

* CYTOKINESIS = 2 cells

Mitosis- produces identical cells

MITOSIS• Prophase• Metaphase• Anaphase• TelophoseCYTOKINESIS

CYTOKINESIS

• Cleavage furrow in Animal cells.

• Cell Plate in Plant cells.

Can you name the stages and the organelles

involved???

MEIOSIS• Process of nuclear division that reduces the number of

chromosomes in new cells to half the number in the original cell.

• Chromosomes no longer in pairs.• This 1/2ing of the chromosome number allows for the

fusion of cells later in the life cycle of the organism.• The chromosome in one gamete can find its’ “pair” in

another gamete through the fusion of sperm & egg.

• In humans MEIOSIS results in either

-4 sperm cells from 1 sperm producing cell or

-1 egg cell & 3 polar bodies from 1 egg producing cell

• Egg and Sperm combine chromosomes in sexual reproduction to produce a diploid zygote.

GAMETES- haploid reproductive cellsSPERM (spermatogenesis) & EGGS (oogenesis)

MEIOSIS ONEhomologous chromosomes

separate

Genetic recombinationOccurs during meiosis 1:1. Crossing Over2. Independent assortment

Crossing over Independent assortment

STAGES OF MEIOSISMEIOSIS 1- homologous replicated chromosomes divide = pairs are split.Prophase 1- DNA condenses into chromosomesMetaphase 1- tetrads align on the metaphase plateAnaphase 1-homologous replicated chromosomes pulled ApartTelophase 1-nuclei form… Q: Cells are haploid or diploid at the end of meiosis 1?A: HAPLOIDMEIOSIS 2- chromatids of the replicated chromosomes are separated.Prophase 2-DNA condenses into chromosomesMetaphase 2-replicated chromosomes align on the metaphase plateAnaphase 2-chromatids separateTelophase 2-nuclei form…Q: What does the chromosome behavior in Meiosis 2 remind you of?A: MITOSIS

PROPHASE 1 • SYNAPSIS is the

pairing of homologous chromosomes.

• TETRAD is each pair of homologous chromosomes.

• CROSSING OVER is when portions of chromatids break off and attach to the adjacent chromatid on the homologous chromosome.

• This results in GENETIC RECOMBINATION!

Crossing Over occurs during PROPHASE 1 of

MEIOSIS• Homologous chromosomes pair up in a tetrad.

• Non sister chromatids get tangled and switch places.

• RECOMBINANT chromosomes are created.

• = new combinations.

METAPHASE• Tetrads align on the

metaphase plate.• Spindle fibers from one

pair of centrioles attach to one replicated chromosome of the tetrad pair.

• Spindle fibers from the other pair of centrioles attach to the other replicated chromosome of the tetrad pair.

ANAPHASE 1• INDEPENDENT ASSORTMENT is

the random separation of the homologous chromosomes based on how the tetrads line up during METAPHASE

• Think of it as “shuffling” the chromosomes. There are many different combinations of the chromosomes possible… each side gets one out of two of each chromosome.

• Independent assortment happens during ANAPHASE 1.

CAN YOU FIND THE PATTERN?

1 pair of chromosom

es

2 X 1 = 2 2 kinds of gametes

2 pairs chromosom

es

2 X 2 = 4 4 kinds of gametes

3 pairsChromosom

es

2 X 2 X 2 = 8

8 kinds of gametes

4 pairs chromosom

es

2X2X2X2=16

16 kinds of gametes

How many kinds of gametes for Humans w/ 23 pairs of chroms?

HOW MANY DIFFERENT TYPES OF GAMETES CAN

YOU MAKE?

DID YOUR PARENTS MAKE WHEN THEY MADE YOU?

WHY DOES THIS MATTER?

• FORMULA = (2) 23 or (2) # chromosomes

• 2 (because there are two copies of each chromosome: one from mom & one from dad) raised to the 23rd power (because humans have 23 chromosomes.)

• 2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2 = 8,388,608

• 1/8,388,608 x 1/8,388,608 =• 1/70,368,744,180,000 = that your parents

will have another “YOU”• YOU ARE SPECIAL!!!

Meiosis II• CELLS ARE

HAPLOID• Although,

chromosomes are replicated.

• Is ESSENTIALLY mitosis.

• Chromatids separate.

MEIOSIS TWOsister chromatids separate =

similar to mitosis.

Note the difference… the cells are already haploid. Only one Color of each kind of chromosome in each cell.

MITOSIS QUESTIONS 1-111. Cell cycle : Interphase (G1, S, G2) 90% of the cell’s life. It grows

and during S phase it copies/replicates it’s DNA)M phase (P,M,A,T) Karyokinesis- division of the

nucleus. Replicated chromosomes line up on the metaphase plate and Chromatids are separated. Two identical nuclei are formed.

Cytokinesis- division of the cytoplasm via cleavage furrow (microfillaments pulling like a drawstring on sweatpants) in animal cells and cell plate formation (cellulose delivered by vesicles) in plant cells.

2) Fingers = spindle fibers Hands = centriolesChromosomes don’t move on their own…

the microtubules formed by centrioles attach to the centromeres of the replicated chromosomes and move them around. :)

3) The chromosomes are NOT lined up in any particular order during prophase of mitosis.

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