Unit 10 Cell Division and Chromosomes

Mitotic Index

# of cells in mitosis/ total # of cells. higher the MI--> cacnerous. treatment: by stopping cell division, so if the treatment is working, fewer cells will be in mitosis. so the MI will decrease if treatment is working.

Prokaryotic Chromosomes

naked, not wrapped around histone proteins, Because there is only a single chromosome there is only one copy of each gene. chormosomes found in cytoplasm

Use of karyogram to diagnose down syndrome

nondisjuction of chrosome #21

Explain how cyclins affect control the progression of a cell thru the cell cycle

1) cells cannot progress to the next stage of the cell cycle unless specific cyclin reaches its threshold 2) Cyclins bind to enzymes called cyclin-dependent kinases 3) These kinases then become active and attach phosphate groups to other proteins in the cell. 4)The attachment of phosphate triggers the other proteins to become active and carry out tasks (specific to one of the phases of the cell cycle). Progression through parts of the cell cycle are affected in various ways by specific cyclins

Advantage of being DIPLOID

2 copies of each chromosome, have 2 copies of each gene that the chromosome contains. so, if one of the chromosomes carries a detrimental allele of a gene, there is a second copy of the gene whose allele may be able to counter the effects of the negative version.

Sister Chromatid

2 identical copies each chromosome consists of attach to form a double chromosome. after DNA is replicated attached to one another at the centromere. start of division, after replication has occurred

Minimum chromosome # in eukaryotes

2n=2 (always an even number for a species bc of sexual reproduction, each parent gives 1 set of chromsomes

Animal cells Cytokinesis

A ring of contractile protein (microfilaments) immediately inside the plasma membrane at the equator pulls the plasma membrane inward. The inward pull on the plasma membrane produces the characteristic cleavage furrow. When the cleavage furrow reaches the centre of the cells it is pinched apart to form two daughter cells.

Explain the relationship between a sister chromatid and a duplicated chromosome.

A sister chromatid is each identical DNA copy attached at the centromere and a duplicated chromosome is two sister chromatids attached at the centromere.

Chromatin

basic unit of chromatin is the nucleosome connected by sections of linear DNA

Autosomes

Autosomes are the homologous chromosome pairs in sexually reproducing organisms that are not involved in gender determination. chromosomes 1-22 NON SEX found in all cells

Cyclin A Normal

Cyclin A can regulate multiple cell cycle steps because it activates two distinct CDKs. In S phase, the cyclin A-CDK complex initiates DNA replication and ensures that DNA is replicated once per cell cycle In G2 phase, the cyclin A-CDK complex prepares the centrosome (pair of centrioles) for mitosis

Cyclin B Normal

Cyclin B is necessary for the progression of the cells into and out of mitosis phase of the cell cycle. At the end of S phase the cyclin B-CDK complex serves to trigger entry into prophase (only if DNA replicated properly in S phase). The active cyclin B-CDK complex phosphorylates a target protein that is necessary for proper creation of the mitotic spindle. In order for the cell to being anaphase, the degradation of cyclin B is necessary.

G1

Cells performing their differentiated function A lot of protein synthesis and metabolism is occurring Numbers of organelles increase. cell growth (acquries nutrients), cell performs specialized function (protein synthesis) the cell grows rapidly, while performing routine metabolic processes. makes proteins needed for DNA replication/copies some of its organelles in prep for cell division. spends most life in this phase. increase volume of cytoplasm

DNA During Cell Cycle

Chromatin (DNA Wrapped around proteins)--> G1 Replicated Chromatin (2 copies of the DNA loosely coded)--> after S, G2 Replicated chromosome (2 identical copies of condensed chromatin, attached at the centromere)--> Prophase, Metaphase Unreplicated Chromosome (Single copy of DNA chromosome)-->Anaphase, telophase, goes back to chromatin and uncoils

The Chromosome Body

Chromosomes are usually stained with a chemical called Giemsa to increase their visibility. This produces a unique pattern of light and dark bands along the body of the chromosome. Each band may contain hundreds of genes. A gene is a section of DNA that can be transcribed into RNA. Active genes (those that are transcribed frequently) are located in the light bands. The dark bands contain less active genes and genes that are tissue specific (only expressed in very specific cell types).

Telophase

Chromosomes arrive at the poles. The chromosomes uncoil de-condense to chromatin (and are no longer visible under a light microscope)Microtubule spindle fibers disappear New nuclear membranes reform around each set of chromosomes each nucleus 2n=4 (diploid) 2 identical nuclei nuclear membrane reforms, nucleoulus reappears, chromosomes decondeses into chromatin spindle fibers break apart

Anaphase

Continued contraction of the microtubule spindle fibres cause the separation of the sister chromatids The chromatids are now referred to as chromosomes Chromosomes move to the opposite poles of the cell. the identical chromatids (now unreplicated chrmosomes) are pulled towards poles of cell by motor proteins

Normal Cyclin D

Cyclin D begins being synthesized during early G1. Once at a high enough concentration, Cyclin D triggers the cell's transition from G1 to S phase. The active cyclin D-CDK complex phosphorylates a target protein that is a tumor suppressor. Before the target protein is phosphorylated (when cyclin D levels are low), the tumor suppressor protein STOPS the cell from moving into S phase. The cell will stay in G1. After the target protein is phosphorylated (when cyclin D levels are high), the tumor suppressor protein no longer stops the cell from moving into S phase... so the cell moves into S phase and begins to replicate its DNA.

Cyclin E Normal

Cyclin E begins being synthesized midway through G1. Once at a high enough concentration, Cyclin E triggers the cell's transition from G1 to S phase. The active cyclin E-CDK complex phosphorylates a target protein that gets DNA ready for replication. Before the target protein is phosphorylated (when cyclin E levels are low), the DNA will not prepare for replication. After the target protein is phosphorylated (when cyclin E levels are high), the DNA will prepare for replication.

Cyclins

Cyclins are a family of proteins that control the progression of cells through the cell cycle. Cyclins activate cyclin-dependent kinase (CDK) enzymes (enzyme that adds phosphate groups to other molecules (phosphoylation, must be attached to a cyclin in order to be active and able to phosphorylate. Active CDK complexes are able to phosphorylate target proteins that then do jobs related to moving the cell through the phases of the cell cycle. There are four different types of cyclins The different cyclins are active at different times of the cell cycle. cell cycle must be controlled so that cells are only dividing when necessary, not constantly. cells need to time progression so that it only moves to one phase to the next only when all the steps are complete.

Chromatids

DNA condenses/coils into the familiar X shaped form of a chromosome only after is has replicated. b/c DNA has already replicated, each chromosome consists of 2 identical copies. 2 copies are called sister chromatids. they are attached to one another at a region called the centromere

Sexual Reproduction

During sexual reproduction, a diploid cell from each parent undergoes a specialized form of cell division to produce gamete cells. The gamete cells are haploid and specialize to become sperm or eggs. Fertilization fuses the haploid sperm and egg to produce a single diploid cell (called a zygote), which becomes the first cell of the offspring.

Plant Cells Cytokinesis

During telophase, membrane-enclosed vesicles derived from the Golgi apparatus migrate to the centre of the cell. Vesicles fuse to form tubular structures. The tubular structures merge (with the addition of more vesicles) to form two layers of plasma membrane (i.e. the cell plate) The cell plate continues to develop until it connects with the existing cell's plasma membrane. This completes the division of the cytoplasm and the formation of two daughter cells. Vesicles deposit, by exocytosis, pectins and other substances in the lumen between the daughter cells to form the middle lamella ('gluing' the cells together) Both daughter cell secrete cellulose to form their new adjoining cell walls.

Haploid Cells

Haploid cells do not contain homologous chromosome pairs. A haploid cell only contains one member of each homologous chromosome pair. The gamete cells (sperm and egg) are haploid. Haploid cells thus contain half the number of chromosomes of diploid cells. Haploid cells are designated N. Haploid cells are produced by meiotic cell division. cell or organism contains 1 set of chromosomes, no chormosome pairs. n=23 (human) egg/sperm no homoglous pairs

Homologous chromosomes

Homologous chromosomes are chromosome pairs that carry the same complement of genes with one member of the pair inherited from the father and the other from the mother. Pairs of chromosomes carry the same complement of genes with one mem (same size, centromere in same position, carry same # and type of genes, shape, contain genes for same trait) Homologous chromosomes are not identical to one another because the DNA sequence of a gene at a particular locus may vary from its homolog. Homologous chromosomes differ from a duplicated chromosome since they are not identical and do not originate from the same organism. Duplicated are identical. IN ALL CELLS EXCPET SEX CELLS. alleles carried at each locus may vary. same size/structure/same genes at same locai 22 are homolgous

Diploid Cells

Humans (and most other sexually reproducing organisms) contain two types of cells; diploid and haploid. These cells differ in their chromosome content. Diploid cells contain homologous chromosomes; pairs of chromosomes that carry the same complement of genes with one member of the pair inherited from the father and the other from the mother. Chromosomes that are homologous are almost always the same size, have their centromeres in the same position and carry the same number and type of genes. (An exception to this rule will be described later in the tutorial.) Homologous chromosomes are not identical because the DNA sequence of a gene at a particular locus may vary from its homolog. Alternative versions of a gene are called alleles. 2n=46 (humans) cell contains 2 complete sets of chromosomes (one from each parent. has homologus pairs, normal #of chromosomes

Cyclin D Cancer

In some cancers (usually colon and melanoma), the cell makes Cyclin D when it shouldn't. As a result, the target protein remains active... "tumor suppression" is off and the cell moves to S phase even if it shouldn't. This results in too many cells moving through the cell cycle even though they shouldn't → TUMOR.

Sex chromosomes

In sexually reproducing organisms, there is one pair of chromosomes involved with gender determination. These are called the sex chromosomes. In humans, the sex chromosomes of a female are perfectly homologous and designated XX. In males, the sex chromosomes are NOT homologous and designated XY. The X chromosome contains roughly 2000 genes while the Y chromosome contains roughly 300. A small portion of the two chromosomes are homologous and in males they behave as a homologous pair. The homologous chromosome pairs in sexually reproducing organisms that are not involved in gender determination are called autosomes.

Cyclin E Cancer

In some cancers (often breast, lung, stomach and colon), the cell makes Cyclin E when it shouldn't. As a result, the target protein remains active... so the DNA prepares for replication even if it shouldn't. This results in too many cells moving through the cell cycle even though they shouldn't → TUMOR.

Mitosis

Mitosis is the division of the nucleus into two genetically identical daughter nuclei. except sex cells. mitosis is required during embryonic develpment (start out w one cell, used to make a lot of cells very quickly in embryonic devl), for organism growth (organisms get larger, bigger than a baby bc more cells now, they are the same size, just more), ALL those cells created by mitosis (allows for growth) For tissue repair (repair those cells, new skin cells form thru mitosis, skin will repair over time, hair grows by mitosis, after injury or burn) For asexual reproduction (organisms small enough can reproduce their whole selves thru mitosis, bacteria yeast) following mitosis, each new nucleus is diploid (2n) with a complete set of chromosomes. chromsomes must be supercoiled during mitosis when chromsoomes need to be short/compact enough that they can be separated and moved to each end of cell.

The development of a primary tumours (cancers) have been outlined. Below is how a primary tumor can become a secondary tumour.

Primary tumor: is a malignant tumor growing at the site where the abnormal growth first occurred. Cancerous cells can detach from the primary tumour. Some cancerous cells gain the ability to penetrate the walls of lymph or blood vessels and hence circulate around the body The circulating cancerous cells invade tissues at a different locations and develop, by uncontrolled cell division, into a secondary tumours. Metastasis is the movement of cells from a primary tumour to set up secondary tumours in other parts of the body.

4 phases of Mitosis

Prophase, Metaphase, Anaphase, Telophase

G2

Protein synthesis and metabolism is occurring to create the molecules needed for mitosis Numbers of organelles increase. the cell makes the proteins required for mitosis/cytokinesis. cell mkaes final preps to divide, makes additional proteins/organelles

Explain the relationship bt oncogens, tumor suppressor genes and cancer

Proto-onco genes are normal genes that code for proteins (cyclins) that help the cell move thru the cell cycle. when protoonco genes are mutated, they become oncogenes, which can move the cell thru the cell cycle even when it shouldn't divide. Tumor suppresor genes function to stop a cell from dividing when it shouldn't. tumor supressors can mutate leading to the cell moving thru the cell cycle when it shouldnt. cancer develops when both types of genes are mutated and the cell divides without control.

Karyotype

Scientists study the chromosome content of cells by creating a karyotype. To construct a karyotype, the chromosomes are photographed while the cell is dividing. The photograph is enlarged and the image is printed or scanned into a computer. The scientist can then cut and paste the chromosomes so that homologues can be paired and ordered by size. This organization allows the scientist to search for defects such as extra or missing chromosomes, and mutations within the chromosomes. number and visual appearance of the chromosomes in the cell nuclei of an organism or species. Karyotypes are what scientists create in order to study the chromosome content of cells.

Similarities/Differences between homologous chromosomes

Similarities: same genes at the same locus, majority of the same DNA base sequence, same length, same centromere position, same staining patttern. Differences: different origin (one mom, one dad), different alleles of the gene

Metaphase

Spindle fibres from each of the two centrosomes attach to the centromere of each pair of sister chromatids Contraction of the microtubule spindle fibres cause the sister chromatids to line up along the centre of the cell. replicated chrmosomes align at cell equator, centromere connected to microtubules (type of spindle fiber)

S

The cell replicates the DNA in the nucleus so that after mitosis both the new cells have a complete set of genes. DNA replicates. DNA replication allows for the chromosome number to double

Outline the formation of a diploid cell from 2 haploid gametes

gametes (egg/sperm) are haploid, means they have ONE complete set of chromosomes. when the gametes fuse during fertilization, the 2 sets of chromosomes (one from egg, one from sperm) combine to create a diploid zygote.

How is a karyotype made?

To construct a karyotype, the chromosomes are photographed while the cells is dividing. The photograph is enlarged and the image is printed or scanned into a computer. The scientist can then cut and paste the chromosomes so that homologues can be paired and ordered by size. This organization allows the scientist to search for defects such as extra or missing chromosomes and mutations within the chromosome.

Description of methods used to obtain cells for karyotype analysis (amniocentesis)

amniotic fluid taken using a syringe. needle is guided using ultrasound. amniotic fluid contains cells from fetus , these cells used for karyotyping (chorionic villus sampling) the chorion is a membrane part of placenta. contains many cells used to create karyotype

Structure/function of 2 human sex chromosomes

X chrosome is larger of the 2 sex chromosomes y chromosome is smaller. chromosome #23 found in ALL CELLS X carries many genes in the non-homologous region which are not present on Y. The presence and expression of the SRY gene on Y leads to male development. Chromosome pairs segregate in meiosis. Females (XX) produce only eggs containing the X chromosome. Males (XY) produce sperm which can contain either X or Y chromosomes.

Cancer

a disease that occurs when the cell cycle is no longer regulated, may happen due to a cell's DNA being damaged. damage can occur b/c of exposure to hazards such as radition/toxic chemicals. cacnerous gells divide much faster than normal cells. may form a mass of abnormal cells (tumor) the rapidly dividing cells take up nutrients/space that normal cells need. which damages tissues/organs__ death

Chromosome

a molecule of DNA that is supercoiled around proteins so it can fit into the nucleus of a cell. in humans, the DNA molecule of a single chrosome ranges between 14 and 73 mm in length. made up of DNA/proteins, form of genetic matieral of a cell during cel division. during other phases of the cell cycle, DNA is not coiled into chromosomes, instead it exists as grainy material called CHROMATIN. linear segments of DNA wrapped around proteins, contains many genes . Chromosomes can vary by: Length - the number of base pairs in the DNA molecule Position of the centromere Genes occur at a specific locus (location), i.e. it is always found at the same position on the same chromosome (the locus and genes possessed vary between species)

Genome

all of the traits that an individual's DNA codes for. Genome size is the total number of DNA base pairs in one copy of a haploid genome.

Tumors

are abnormal growth of tissue that develop at any stage of life in any part of the body. A cancer is a malignant tumour and is named after the part of the body where the cancer (primary tumour) first develops. Use the links to find out: most common types of cancer what causes cancer and associated risk factors how cancer can be treated. put a lot of pressure on organs, can cause problems even with benign tumor Benign- non cancerous tumor,cells not cancerous, don't express the gene Malignant: cancerous tumor, have elevated lvevels of cyclins, dividing so quickly piling up, can invade other tissues or metasize

Mutagens

are agents that cause gene mutations. Not all mutations result in cancers, but anything that causes a mutation has the potential to cause a cancer. Mutagens can be: chemicals that cause mutations are referred to as carcinogens high energy radiation such as X-rays short-wave ultraviolet light Some viruses Factors (other than exposure to mutagens) that increase the probability of tumour development include: The vast number of cells in a human body - the greater the number of cells the greater the chance of a mutation. The longer a life span the greater the chance of a mutation. (carcinogen--> may increase risk, not necessarily get cancer, capable of causing cancer, not all mutagens are cacinogens) Mutagens are not necessarily carcinogens since a mutagen induces mutations in DNA, if the mutagen results in uncontrolled cell division and cancer, then the mutagen is also a caricinogen.

Chromosomes arranged on the karyogram

arranged by size (largest-smallest), banding pattern and centromere position

Knowledge gained from Autoradiography techniques

autoradiography: used to produce an image of a radioactive substance. used to visualize chromosomes, bands of DNA, tissue samples, single cells

Oncogene

cancer gene, controls cyclin production, typically turned off (not expressed, in every cell), mutation--> causes them to be turned on

G0

checkpoint, resting phase, cell will stop until it gets a signal to divide (sicklins--> signals, control cell cycle) control how quickly cell cycle can happen cell is neither dividing or prepping to divide

Eukaryotic Chromosomes

consist of 3 distinct regions: the telomeres (tips of chromosomes), the centromere(constricted region of chromosome) and severl hundred to several thousand genes found along the "body" of the chromsome humans have 46 chrosomes or 23 pairs arranged by size.

Centromere

constricted (narrowed area) on chromosome is called centromere. composed of about several million base pairs with a repitive base sequence. the centromere has 2 functions-prior to cell division, every chrosome in cell is replicated. the identical DNA copies are held together at the centromere (each identical DNA copy attached at the centromere is called a sister chromatid). 2 sister chromatids attached at the centromere is called a duplicated chrosmome. also serves as an attachment site for the spindle microtubles during cell division so the chrosomes can be moved and distrbuited bt daughter cells. location where the 2 idenital DNA strands (sister chromatids) are attached

Cytokinesis

division of the cytoplasm of a parent cell into 2 daughter cells. ccurs concurrently with telophase.

Determine sex of an individual given karyogram

examine last pair of chromosomes, XX-female XY-male

Human Chromosomes

human cells normally have 2 sets of chromosomes, one set inheretied from each parent. 23 chromosomes in each set, total of 46 chromosomes per cell. each chromosome in one set matched by a chromosome of the same type in the other set, so there are actually 23 pairs of chromosomes per cell. each pair consists of chorosomes of the same size, shape that also contain the same genes. the chromosomes in a pair are known as homologous chromosomes.

Mutation

is a change in an organisms genetic code. A mutation/change in the base sequence of a certain genes can result in cancer. if a mutation occurs in an oncogenes it can become cancerous. In normal cells oncogenes control of the cell cycle and cell division. mutation in a oncogene--> malfunction in the control of the cell cycle--> uncontrolled cell division--> tumor formation Several mutations must occur in the same cell for it to become a tumour causing cell. The probability of this happening in a single cell is extremely small. Cell becomes cancerous after mutations accumulate in the genes that control the cell cycle

Cell Cycle

is the events that take place in a cell leading to its division that produces two identical daughter cells. made up of 4 phases (g1, s, g2, mitosis) repeating series of events, including growth, DNA synthesis, cell division. CELL CYCLE PROKARYOTES: the cell grows, DNA replicates, cell divides Eukaryotic Cell Cycle: Mitosis (mitosis/cytokinesis), nucleus/cytoplasm divides. interphase, cell grows, performs routine life processes, prepares to divide

Prophase

just before prophase, the cell has 2 copies of every chormosome. DNA already replicated by S phase, choromsomes form. DNA supercoils* into replicated chromosomes chromatin condenses and becomes sister chromatids, which are visible under a light microscope The nuclear membrane is broken down and disappears he centrosomes move to opposite poles of the cell and spindle fibres begin to form between them nucloeous dissapears spindle fibers form and centrioles move towards the cell poles

Karyogram vs karyotype

karyogram-graphical/photographic representation of the karyotype. karyotype- characterisitcs of the chromosomes of an indivudal (number, type, shape) diagram/photograph of the chromosome present in a nucleus (of a eukaryotic cell) arranged in homologous pairs of decreasing length The chromosomes are visible in cells that are undergoing mitosis - most clearly in metaphase. Stains used to make the chromosomes visible also give each chromosome a distinctive banding pattern. A micrograph are taken and the chromosomes are arranged according to their size, shape and banding pattern. They are arranged by size, starting with the longest pair and ending with the smallest. Karyotype is a property of the cell described by the number and type of chromosomes present in the nucleus (of a eukaryote cell). a Karyogram is a diagram that shows, or can be used to determine, the karyotype.

Why do Cells divide?

large cells have a small SA:V ratio, much less efficient than smaller cells. if an organism grows larger, it needs to produce more cells and each of those cells needs a copy of the organism's DNA. allows for growth of organism/cell differentiation.

Describe the structure of eukaryotic DNA and associated histone proteins during interphase (chromatin)

linear associated w histone proteins in a strucutre called the nucleosome. during interphase, the DNA is not supercoiled into chromosomes, it's in a loose form called chromatin Nucleosomes are formed by wrapping DNA around histone proteins Eukaryotic chromosomes may be up to 85mm in length. To fit such a length of DNA into a nucleus with a diameter of 10 μm it has to be coiled in a predictable fashion that still allows for processes, such as Eukaryotes possess multiple chromosomes. All individuals of a species possess the same chromosomes, with the same gene loci. For example all humans have twenty three pairs.

Interphase

majority of cell cycle spent here . during g1 cell is performing its specialized function, which requires extensive protein synthesis. during S, DNA replication occurs. consists of parts of the cell cycle that don't involve cell division. cell carries out normal life functions (metabolic reactions--> respiration to produce ATP, protein synthesis--> protein/enzymes needed to allow cell growth, organelle # increases--> support the enlarged cell, DNA is replicated--> to ensure a second copy is avaliable to enable mitosis)

Chromosome #/type is a distinguishing characteristic of species

organisms with differing # of chromoosmes are not likely to interbreed, all the members of a species will have the same # of chromsomes Mechanisms by which the chrosome # can change of a species: chrosome splitting (increase # of chro.) choromse fusing (decrease #)

Chromosome # of a species doesn't indicate the # of genes in a species

possible to have one large chromosome w many genes, or many smaller chromosomes w fewer genes. large chromsomes w few genes or smaller chromosmes packed w genes . Species have different numbers of chromosomes than other species All eukaryotic species have at least two chromosomes. The number of chromosomes in a species has no specific significance nor does it indicate any relationship between two species.The number of chromosomes does NOT correlate to the number of genes

John Cairns

produced images of DNA molecules from Escherichia coli (E.coli) E. Coli was grown with thymidine containing a radioactive isotope of hydrogen (the DNA was labelled). The E. Coli cells were broken open by enzymes to release the cell contents The cell contents were applied to a photographic emulsion and placed in the dark (for two months) The radioative isotopes reacted with the emulsion (similarly to light does) Dark areas on the photographic emulsion indicated the presence of DNA The images showed that E. coli possesses a single circular chromosome which is 1,100 μm long (E. coli cells have a length of only 2 μm) Cairns images also provided evidence to support the theory of semi-conservative replication able to see that prokaryotic chromosomes are circular observed DNA replication occuring at the replication fork

Telomeres

repitive base sequence on tips of chromosome. in humans this sequence is TTAGGG and may be repeated hundreds/thousands of times. the telomeres prevent adjacent chromosomes from fusing together and prevent the loss of the essential genes in the body of chromosome during DNA replication.

Chromosome #

s an important characteristic of the species. Organisms with different numbers of chromosomes are unlikely to be able to interbreed successfully Chromosomes can fuse or spit during evolution - these are rare events and chromosome numbers tend to stay the same for millions of years. The number of chromosomes possessed by a species is known as the N number, for example humans have 23 different chromosomes. A chromosome number does reflect the complexity of an organism

Gene

segement of DNA bases that code for a specific trait gene locus: location of a gene on a chromosome, specific poisition of a gene on a chrom. heritable factor that controls or influences a specific characteristic, consisting of a length of DNA occupying a particular position on a chromosome (locus) all individuals of a species carry the same genes at the same locai on the same chromoomses. alleles: different forms of a specific gene

List ways in which the types of chromosomes within a single cell are different

size, number of base pairs, which genes they carry, sequence of nitrogenous bases, location of centromere, banding pattern when stained

Genes

the DNA of a chromosome is encoded with genetic instructions for making proteins. these instructions are organized into units called genes. most genes contain the instructions for a single protein. there may be hundreds/thousands of genes on a single chromosome.

Explain why chromosomes must condense during mitosis

to "condense" means to make DNA denser or more tightly packed. DNA condenses during mitosis so that it can more easily be moved to the poles of the cell.

Cyclin B Cancer

when cyclin B levels are elevated, cells can enter mitosis prematurely (and therefore divide when they shouldn't) Some anti-cancer therapies have been designed to prevent cyclin B/CDK complex formation in cancer cells to slow or prevent cell division.