LIVING ENVIRONMENT UNIT 8; 🧬🦠 MITOSIS AND MEIOSIS🦠🧬

** Mitosis **

- the division of body/somatic cells

- In humans, these create cells with 46 chromosomes,

- used for tissue growth and repair

* in most multicellular organisms, cell division does not result in the creation of a new organism. *

- happens during the Prophase, Metaphase, Anaphase & Telophase part of the cell cycle.

- usually how asexual reproduction occurs

(CHECK PAKCET )

How many chromosomes does a human have and why?

- Humans have 23 chromosomes

- 23 chromosomes are necessary because if we had the full 46 chromosomes in our gametes, when the cells combine the chromosome count would double making a 96 chromosome human (?? )

- ( not good )

** Meiosis **

- A kind of cell division that results in the creation of gametes with half the number of chromosomes (23) as the parent cell (46)

( reduction and division !!)

- occurs in testes and ovaries

( sperm and egg ) (( fertilization ))

- starts in one diploid cell ( a cell with 46 chromosomes in ovaries and testes )

- The process of meiosis occurs in two parts , Meiosis I and meiosis II

- These phases are similar to mitosis

( Prophase, Metaphase I, Anaphase I, Telophase I, Metaphase II, Anaphase II, Telophase II and Metaphase II )

-

* in humans, this creates cells with 23 chromosomes *

( CHECXK BOTH PACKETS )

Each pair of chromosomes, one from Mom and one from Dad are known as what??

- Homologous Chromosomes

Homologous Chromosomes

- a pair of chromosomes that are similar in size and shape and have similar genetic content

- each pair contains one chromosome from mom and the other from dad

- Cells that are homologous are known as somatic cells

( body cells ) , diploid cells or 2n

(CHECK DIAGRAM)

Somatic cells

- body cells that have 46 Chromosomes in humans ( 23 pairs )

- same thing as body cells/diploid cells/ 2n

(dip- di= two )

Haploid cells

- a cell with one of each kind of chromosome,

- these cells are our sex cells ( gametes )

(halp- =half )

* Compare and Contrast Meiosis and Mitosis *

· Mitosis;

- purpose;

- growth and repair of tissue

- used in the growth of a zygote

-used in the healing process of a cut

- location;

- all body cells

· Meiosis;

- purpose;

- creates gametes ;

--> sperm

---> egg

- location;

- gonads

--> testes

---> ovaries

** precede sexual reproduction!! **

· Both;

- Create cells !

- chromosomes are being replicated in the process

- start with a diploid cell

- occur during prophase, anaphase, metaphase and telophase.

( CHECK PACKET )

Cytokenesis

- the division of the cytoplasm

* Why are cells so small and why do they need to divide before they get too big? *

- diffusion limits size

( glucose/ channel protein, oxygen/phospholipid membrane )

* over long distances, diffusion becomes slow and inefficient *

* big cells would starve or die of a build up of wastes if they got too large. *

What does a cell do before it gets too large?

- divide.

* Note about cell division *

- in most multicellular organisms, cell division does not result in the creation of a new organism.

When a eukaryotic cell divides it takes place in two stages which are..

- Mitosis;

- when the nucleus divides to form 2 nuclei

- Cytokinesis;

- when the cytoplasm divides to create 2 cells.

Changes in the Nucleus

- the nucleus of a cell plays a major role in cell division

- in non-dividing cells, DNA exists as chromatin

- when mitosis begins, chromatin shortens and thickens into rod like structures called chromosomes

- all chromosomes must be present for the organism to work/function properly.

* NOTE ABOUT DNA *

- all DNA in the body is identical, no matter the cell type

- the only thing different about the DNA present in the body is which parts of it are turned on and off to form different cells.

* Nucleus *

- holds the codes for proteins made by the cell called DNA

( deoxyribonucleic acid )

* DNA *

- a.k.a deoxyribonucleic acid

- stored in the nucleus, the code for proteins made by the cell

- in non dividing cells, this exists as chromatin.

* Chromatin *

- spaghetti like twisted threads of DNA

- when mitosis begins, this shortens and thickens into rod-like structures called chromosomes.

( check notes )

When mitosis begins chromatin...

shortens and thickens into rod-like structures called chromosomes.

( check notes )

* Each organism has... *

- a different number of chromosomes!

- human - 46

- crayfish - 20

- wheat - 42

Karyotype

- a picture of the chromosomes

- pair 1-23 = autosomes

- pair 23 = sex chromosome ( shows ur sex )

- ( xx = female, xy= male )

What are autosomes?

- the first 23 pairs of chromosomes, usually shown in a karyotype

Which pair of chromosomes are the sex chromosomes?

- pair 23,

- determines your sex ( xx = female, xy = male )

What happens if there is one extra or missing chromosome in a human?

- all chromosomes must be present for the organism to work/function properly

- if there is 1 extra chromosome ( 21 ) its down syndrome.

- if there is one fewer chromosome in a human (23; females) it is turner syndrome.

Cell Cycle

- sequence of growth and division of cell.

( G= gap/growth, S= synthesize )

INTERPHASE

- G1:

- interphase begins

- growth and development occurs

- S:

- Chromosomes are replicated

- G2:

- cell prepares for mitosis

- Centriole replicates

What stages are apart of Mitosis?

- Prophase

- Metaphase

- Anaphase

- Telophase

- remember PMAT!!!

What happens after all of the stages of mitosis in animal cells?

- Cytokinesis!!

- ( when the cytoplasm divides splitting into two cells )

What precedes mitosis?

- interphase

Interphase

- the phase in which a cell is between mitotic cycles.

- * Preceded Mitosis!! **

** Growth period **

- grows in size

- metabolizes

- chromosomes replicate ( not visible )

***** G1, S, & G2 of the cell cycle!!! *****

** Prophase **

- The first and longest phase of Mitosis.

- ** Replicated chromosomes become visible. **

- centrioles move to opposite ends of the cell ( poles )

- Nuclear membrane disintegrates

- Asters form around centrioles

- Spindle fibers form

- Replicated Chromosomes move towards the equator (prometaphase )

( Check notes!! )

Prometaphase

- a stage of mitosis between Prophase and Metaphase

- replicated chromosomes start to move towards the equator.

- replicated chromosomes then attack to spindle fibers.

** Metaphase **

- a stage of mitosis in which replicated chromosomes attach to spindle fibers ( mostly in prometaphase )

- When chromosomes line up mid line ( metaphase )

( Check diagram )

** Anaphase **

- separation of sister chromatids

- each chromatid ( now called a chromosome ) moves to the oppisite pole

- one complete set of chromosomes goes to one pole while a identical set goes to the other.

( check diagrams )

** Telophase **

- phase begins once the chromosomes ( chromatids ) reach the poles

- Chromosomes unwrap --> chromatin

- spindle fiber breaks down

- nuclear membrane reforms

At the conclusion of this phase, cytokinesis occurs.

( check diagram )

** Cytokenesis **

- occurs at the conclusion of telophase

- This is when the..

- cell membrane pinches off

- the cytoplasm divides

- and 2 identical daughter cells complete

- the cells formed through this process are identical and their DNA reverts back to chromatin.

( check diagrams )

Plant cell mitosis

- Plant cells undergo cytokenesis by forming a cell plate which develops into a new cell wall.

- Animal cells undergo cytokenesis by the pinching in of the cell membrane

Differences between plant cells and animal cells in mitosis

- Plant cells do not have centrioles; only a centrosome region

- Animal cells have centrioles within the centrosome region.

Similarities and Differences between Asexual Reproduction and Sexual Reproduction

· Asexual Reproduction

- identical offspring

--> results in natural cloning

- One parent needed to reproduce

ex.

Bacteria (Prokaryotes)

Jellyfish,

Starfish (regenerate)

Plants

· BOTH;

- Produce offspring

· Sexual Reproduction

- Offspring have genetic variation

- needs two parents to reproduce

Sperm + egg = Zygote ( fertilization )

ex.

Humans

Jellyfish

Starfish

Plants

What are some advantages and disadvantages of asexual reproduction

☑️

- Takes less time,

❌

- disadvantage w evolution due to identical offspring

- little variations, only case of variation is mutation

What are some examples of organisms that reproduce through asexual reproduction?

- Bacteria ( Prokaryotes )

- Jellyfish

- Starfish ( regeneration )

- Plants

- Protozoa

- Hydra

- Mushroom/mold

What are some advantages and disadvantages to sexual reproduction?

- ☑️

- Evolutionary advantage ( can adapt to environment )

--> helps species' survive through changes

- genetic variation!

- ❌

-Takes a long time

What are some examples of organisms that sexually reproduce?

- Humans

- Jellyfish

- Starfish

- Plants

- Cat

Asexual Reproduction

- Needs Mitosis to occur

- each offspring had the exact same hereditary information as it's parent ( natural cloning )

- Typically occurs more quickly than sexual reproduction.

Has many types.. including:

- Binary Fission

- Budding

- Spore Formation

- Regeneration

- Vegetative Reproduction/Propagation

* Binary Fission *

- Simplest form of "Mitosis"

- When the parent cell divides into two parts that are equal

ex.

- Fission in Bacteria

- Fission in Protozoa

** Binary Fission in Bacteria **

- occurs in prokaryotic cells with no nucleus

- DNA --> 1 Chromosome

- The chromosome replicated

- the cell wall separated the replicated chromosomes and forms two new cells.

** Binary Fission in Protozoa **

- occurs in a eukaryotic cell called the Protozoa

- undergoes Nuclear division ( mitosis )

- Cytokinesis occurs.

* Budding *

- A type of asexual reproduction in which a parent divides into two unequal parts.

- Parents and offspring are not the same size.

-ex.

- yeast

- hydra

* Spore Formation *

- a.k.a Sporulation

- Spore; specialized cells that are produced by certain organisms

- formed asexually or sexually

- mitotic cell division

- ex. Mushroom, Mold.

( check diagram )

Spore

- specialized cells that are produced by certain organisms.

Regeneration

- a type of asexual reproduction in which an organism has the ability to regrow lost body parts.

- Ex.

- Salamanders ( only tail )

- Starfish ( whole new starfish )

- Crab ( lost claw )

( check diagram !! )

Vegetative Reproduction

- a.k.a Vegetative Propagation

- Most plants reproduce sexually ( seeds ), but asexual reproduction is also possible

- when roots, stems and leaves give rise to a new plant.

- This is possible through the undifferentiated cells

( cambium /epithelial cells )divide mitotically then will differentiate into a new plant

- ex.

-bulbs

-tuber

-runner

- can also be artificially induced.

Bulbs

- a form of natural vegetative reproduction

- a form of asexual reproduction in which short underground stems can give rise to new plants

- ex. tulips, garlic, onion

Tuber

- an enlarged part of an underground stem

- contains stored food

- ex. potato

Runner

- A form of asexual reproduction

- Strawberry plants form a clone from a runner

Artificial vegetative Reproduction/Propogation

- a forced version of Vegetative Propagation/Reproduction which allows farmers to grow plants with desirable traits.

- ex.

- cutting

- grafting

Cutting

- a forced version of vegetative propagation/reproduction

- allows farmers to grow plants with desirable traits

- when a farmer cuts any part of a plant ( stem, leaf or root ) used to grow a new plant

Grafting

- a forced version of vegetative propagation/reproduction

- allows farmers to grow plants with desirable traits.

- when a stem or bus is removed from one plant and joined to another plant of a similar background

- ex.

- roses

- apples

- grapefruit

- oranges

etc.

What happened when a cell loses control of the cell cycle?

- The cell cycle is important to our health, so when cells lose control of this cycle it can have disastrous results

- Cancer is one of the results of uncontrolled cell division

Cancer

- One result of uncontrolled cell division,

- there are many types of cancer but they all start because of abnormal cell growth.

- a protein, called cyclin, regulates the timing of the cell cycle

- when cells start dividing uncontrollably, there may be a problem with the cyclin level in the cell.

- The production of this protein is controlled by genes located on a chromosome

- altered genes can form canerous cells that fotm masses of tissue called tumors.

( some don't.. like leukemia )

- has four stages .

Gene

- A segment of DNA that controls the production of a protein

How can genes be altered

- people can inherit damaged DNA;

- inherited cancers

- breast cancer

- Environmental exposure can also damage DNA;

- skin ( skin cancer )

- smoke ( lung cancer )

- alcohol ( liver cancer )

This altered DNA forms cancerous cells that in turn form masses of tissues called Tumors.

Cancerous cells form masses of tissue called...

Tumors

Tumors

- Cancerous cells that form masses of tissue called tumors,

- Some don't form tumors like leukemia

Benign Tumors

- non cancerous tumors that doesn't spread to other parts of the body and usually not life threatening.

Malignant Tumors

- Cancerous cells that will spread to other parts of the body and invade healthy tissue/cells.

- if untreated death usually results.

Metastasis

- When cancer cells travel to other parts of the body where they begin to grow and replace other healthy cells

travels through

- lymph system

- blood stream

Remission

- a period of time when the cancer is responding to treatment or is under control

- In complete remission, all signs and symptoms of the disease disappear for weeks --> years ---> eventually permanently.

Stages of Cancer

- Stage 1;

- cancer is confined to the organ it started in

- Stage 2;

- cancer is still localized, but the tumor is larger ,than in stage 1.

- Sometimes nearby lymph nodes can be affected.

- Stage 3;

- Cancer is larger and there are cancer cells in the lymph nodes in that area.

- Stage 4;

- Cancer has spread to the major organs in the body.

Sexual Reproduction

- requires two different parent cells. one from mom and one from dad

- Sexual Reproduction produces offspring that are genetically different from either parent.

Fertilization

- the fusion of the nuclei of the male and them female gametes.

Gametes

- sex cells

- Male: Sperm

- Female: eggs

- new life forms when the gametes join together

Zygote

- A single cell formed from the fusion of male and female gametes,

How many chromosomes does a haploid cell have?

- 23 chromosomes

How many chromosomes does a diploid cell have?

- 46

Difference between Meiosis I and Meiosis II

Meiosis I; separates homologous chromosomes

Meiosis II; separates non sister chromatids

*Meiosis stages *

- occurs after interphase,

- occurs in two parts, starts with 1 diploid cell and ends with 4 haploid cells.

- used to create gametes with half the chromosome # and therefore allow for genetic variation.

Prophase I;

- each chromosome has already replicated,

- each homologous chromosome lines up with it's pair and becomes fastened at the centromere, known as synapsis.

- each group of four chromatids is a tetrad

- crossing over occurs in this stage.

Metaphase I;

- Tetrads line up across the equator

( m for middle )

Anaphase I;

- Tetrads separate ( disjunction )

- left with 23 replicated chromosomes!

Telophase I;

- Two daughter cells are formed with half the number of chromosomes as the parent cell.

- Chromosomes are already in their replicated form.

Prophase II;

- Chromosomes move towards the equator

Metaphase II;

- Chromosomes line up on the equator of both daughter cells.

Anaphase II;

- Chromatids separate each becoming a single stranded chromosome

Telophase II;

- Both daughter cells divide, forming 4 haploid (n) cells

( CHECK DIAGRAMS/ ONE IS ON THE TEST )

* Synapsis *

- When replicated, homologous chromosomes line up with their pair and become fastened at the centromere.

* Tetrad *

- A group of four chromatids that are formed through synapsis during Prophase I of Meiosis.

Crossing over

- An exchange of genetic material between maternal and paternal chromosomes

- allows for genetic variation to occur due to genetic recombination.

- occurs during Prophase I, after synapsis had occurred and tetrads are formed.

( CHECK PACKET!! !)

When does crossing over occur in meiosis?

-During Prophase 1, after synapsis has occurred and tetrads are formed.

Disjunction

- a normal occurrence in homologous chromosomes during meiosis

- when chromosomes ( tetrads ) move apart during Meiosis

( specifically Anaphase I )

( a good thing )

Non-disjunction

- an bad/abnormal occurrence when homologous chromosomes fail to move apart/separate correctly during meiosis! ( Anaphase I )

- This is how Down Syndrome results.

Oogenesis

- The creation of egg cells in the ovaries using the process of meiosis.

- One egg ( w 23 chromosomes ) and 3 polar bodies ( duds ) are formed from 46 chromosome oogonium.

* Usually one oogonium undergoes meiosis each month in the ovary. *

( check diagram )

What is formed from a oogonium?

- from a oogonium with 46 chromosomes that was produced in the ovaires

- an egg with 23 chromosomes is produced and

- 3 polar bodies (duds ) are also formed.

How often does oogenesis occur?

- about once a month

What is another word for polar body?

dud

Spermatogenesis

- the creations of sperm cells in the testes using the process of meiosis

- produces 4 sperm cells with 23 chromosomes from a 46 chromosome spermatogonium.

- Millions of spermatogonia are undergoing meiosis constantly in the testes.

How often does spermatogenesis occur??

- constantly !!!!

What is formed from a spermatogonium?

- a spermatogonium with 46 chromosomes produces four sperm cells with 23 chromosomes.

( check notes!! )