Chapter 8- Cellular Reproduction and Development

Chapter 8- Cellular Reproduction and Development

• Anaphase• Anchorage dependence• Asexual reproduction• Autosomes• Benign• Binary fission• Cancer cells• Cell cycle• Cell cycle control system• Cell division• Cell plate• Centromeres• Centrosomes• Chiasma• Chromatin• Chromosomes• Cleavage furrow• Crossing over• Cytokinesis• Deletion• Density-independent inhibition• Diploid• Downs syndrome• Duplication• Fertilization• Gametes• Genetic recombination

• Genome• Growth factor• Haploid• Homologous chromosomes• Interphase• Inversion• Karyotype• Locus• Malignant• Meiosis• Metaphase• Metastasis• Mitosis• Mitotic phase (M phase)• Mitotic spindles• Nondisjuction• Prophase• Sex chromosomes• Sexual reproduction• Sister chromatids• Somatic cell• Telophase• Translocation• Trisomy• Tumor• Zygote

What are the 2 types of reproduction?

• Asexual- production of offspring by single organism– Inherit DNA from one parent– Offspring are identical to parent

• Sexual- reproduction process involving union of sperm and egg– DNA is inherited from both parents– Offspring are a 50% match to each parents DNA– Produces GREAT variation

Chromatin / Chromosomes

• Structure that contains most of the organism’s DNA

• Chromatin coils up into chromosomes in preparation of cell division

Review: Cell Theory

• Cells are the basic unit of structure and function

• All organisms are comprised of cells

• All cells come from pre-existing cells**– Cells produce new cells by cell division- to

grow, develop and reproduce

Prokaryotes:

• Divide by binary fission

• Copied DNA moves to opposite sides of the cell and the cell then splits in two

Eukaryotes

• DNA is packaged into chromosomes• Proteins help organize and package the

DNA• Sister chromatids- two copies of 1

chromosome• Centromere- where chromatids are joined• During cell division- sister chromatids

separate, after separation they are called chromosomes

The Cell Cycle

The Cell Cycle• Interphase (3 phases)

– G1- increase protein supply, increase #’s of organelles, grows in size

– S- DNA replication, single chromosomes duplicate to form two sister chromatids

– G2- proteins that are essential for division are made

The Cell Cycle

• M phase- (2 phases)– Mitosis- nucleus and its’ contents divide– Cytokinesis- cytoplasm is divided– Produces genetically identical daughter cells

Mitosis

• For growth, replacement and asexual reproduction

• 4 phases:

Mitosis

Prophase • Chromosomes are formed, nucleoli disappear, mitotic

spindles begin to form, at the end- nuclear membrane breaks apart

• Mitotic spindle- football shaped group of microtubules that guide chromosome separationg

• Centrosome- where microtubules originate, containing centrioles

• Kinetochore- protein by centromere, is where microtubules attach

Metaphase

• Chromosomes line up along the metaphase plate

Anaphase

• Centromeres come apart, sister chromatids separate, microtubules shorten and poles are moved farther apart, chromosomes move to opposite ends of the cell

Telophase & Cytokinesis

• Telophase- daughter nuclei appear, nuclear membrane reforms, chromosomes uncoil, mitotic spindles disappear

• Cytokinesis- – Animal- by process of cleavage -cleavage furrow,

shallow groove at surface, ring of actin contracts and pinches cell in two

– Plant- vesicles containing cell wall material collect in the middle of cell -vesicles fuse forming cell plate and it’s grows out, membrane of cell plate fuses with plasma membrane and cell wall

What affects the cell division?

• Anchorage dependence- requirement that a cell must be anchored to something to divide, stops loose cells from dividing at an inappropriate time

What affects the cell cycle?

• Density-dependent inhibition- cell division slow as population becomes denser– If cells are scraped off, cells bordering it will divide

until space is again taken up• Growth factor- protein secreted by cells that stimulate

others to divide– Most require it to start, and stop when it runs out

How is the cell cycle controlled?

• Proteins trigger and control cell cycle events– Protein will trigger start

of anaphase

• Signals from outside the cell– Environmental

conditions

Checkpoints

• Checkpoints– G1- before S phase- most important in animal

cells• If doesn’t pass checkpoint- arrested forever • Ex: nerve and muscle cells

– G2- before M phase– M checkpoint- if chromosomes are all

attached to spindles chromatids separate

How are signals to continue cycle relayed?

• Signal transduction- growth factors relay signals to continue cycle

Does it ever go “out of control”?• Cancerous cells- dysfunctional cell cycle control, divides

uncontrollably and can invade body tissues– Tumor- abnormal mass of cells– Benign tumor- excess mass of normal cells, remain in same

place of body– Malignant tumor- cancerous, mass of cancerous cells capable of

spreading into neighboring tissues• Displaces normal tissue as it grows

– Metastasis- spread of cancerous cells beyond original site– 4 categories depending on where they originated– Unrestrained by cell cycle control, not affected by density, don’t

need to be anchored, can synthesize growth factor– Chemotherapy and radiation- attempt to stop cell division

Meiosis

• gamete production, occurs in ovaries and testes, produces cells with ½ chromosome number, haploid cells

Vocabulary

• Somatic cell- body cell

• Homologous chromosomes- same chromosome, same genes, consists of sister chromatids

• Autosomes- chromosomes not involved in sex determination

• Sex chromosomes- X and Y, determines sex

Vocabulary con’t

• Diploid cells- contain 2 homologous sets of chromosomes, 2n, body cells for ex– 2n in humans = 46

• Haploid cells- contain 1 set of chromosomes, gametes, sex cells, n– n in humans = 23

• Fertilization- joining of haploid sperm and egg cells

• Zygote- fertilized egg

Meiosis

• Produces 4 haploid cells• Undergoes 2 divisions: meiosis I and meiosis II• Meiosis I- homologous chromosomes separate• Meiosis II- no duplication, only division• Interphase- same as in mitosis

Steps in meiosis– Prophase 1- similar to mitosis, synapsis- homologous

chromosomes come together in pairs, forming a tetrad (4 chromatids) – crossing over occurs- segments of chromosomes are exchanged

– Metaphase 1- tetrads line up along metaphase plate– Anaphase 1- tetrads are pulled to opposite ends– Telophase and cytokinesis- same as mitosis and is

followed by another interphase before meiosis II– Meiosis II- NO DUPLICATION, similar steps as

meiosis I and mitosis– Results in 4 daughter cells each with ½ the number of

chromosomes as parent cell

Mitosis vs. Meiosis

Sexual reproduction= variation

• Independent assortment- how chromosomes are arranged at metaphase plate meiosis I and II

More ways that affect variation:

• Crossing over- exchange of homologous chromosomes segments– Chiasma- site of crossing over– Results in genetic recombination, produces new gene

combinations

More ways that affect variation:

• Chromosomes carry different versions of genes– Alleles- different versions of a gene

Do mistakes happen in meiosis?

• Nondisjunction- chromosomes do not separate

Nondisjuction

• In autosomes- can be lethal, or can affect survival– Trisomy 21 (Down syndrome)– Trisomy 13 (Patau syndrome), Trisomy 18 (Edwards syndrome)

• In sex chromosomes- abnormalities do not affect survival– Klinefelter syndrome- extra X’s – (male)– XYY- normal male– XXX-metafemale– Turner syndrome- XO- female- absence of Y chromosome– All affect fertility of afflicted individual, except XYY

Do mistakes happen in meiosis?• Chromosomal abnormalities

– Deletion- fragment of chromosome is deleted/lost– Duplication- part of chromosome is added to the homologous

chromosome– Translocation- chromosome fragment is attached to another

chromosome– Inversion- fragment is chromosome is attached in reverse

direction

How can we see the mistake?• Karyotype- magnified image of chromosomes

– Errors in meiosis can lead to gametes with abnormal chromosome numbers

– Fertilization of gametes with abnormal chromosomes numbers can lead to offspring with chromosomal abnormalities

– Ex: Down syndrome- trisomy 21

Do humans help out what traits get passed down?

• Selective breeding- breeding certain individuals with desired traits– Crops– Racehorses– Farm animals– Dogs