Part 1: Chromosomes. All living things are made up of one or more cells. These cells all contain DNA (deoxyribonucleic acid) which is your genetic.

Part 1: Chromosomes

All living things are made up of one or more cells.

These cells all contain DNA (deoxyribonucleic acid) which is your genetic material.

DNA can be stored in two forms as either chromatin (relaxed or unraveled) or as chromosomes (coiled)

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Chromatin coils to form a chromosome.

Chromosomes are rod shaped and comprised of both DNA and proteins called histones.

Histones are proteins that help the DNA maintain the coiled shape of a chromosome.

DNA needs to be relaxed in order to be read. However, it is never completely uncoiled as it would take up too much space. And it is never super coiled into a chromosome unless a cell is dividing.

Most of the time, your cells are not dividing. Therefore you have unduplicated chromosomes.

A dividing cell will have a duplicated chromosome which is made up of identical chromatids

Constricted area is the centromere

This is a eukaryotic chromosome. Prokaryotic organisms only have one chromosome and it is round.

What kind of chromosome is this?

Chromosomes contain genes which are areas of DNA that code for particular proteins.

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There are two types Sex Chromosomes: determine the sex

(gender) of an organism Autosomes: does not determine

gender Every cell has two copies of each

autosome – 1 from mother and 1 from father called homologous chromosomes or homologues

Homologous chromosomes carry the same type of genetic information but it may not be identical• Every cell has 2 sex chromosomes

that can differ depending on what they receive from their parents

• XX – female• XY – male

Does the number of chromosomes have anything to do with the complexity of an organism?

Photomicrograph of the chromosomes in a dividing cell

Human karyotypes show 22 homologous pairs of autosomes and 2 sex chromosomes

What do you notice about the arrangement?

Is this a male or female?

Diploid (di=2) cells have two sets of chromosomes• All normal human cells (except

reproductive) are diploid and called somatic (body) cell

• Represented by 2n Haploid (one) cells only have one set of

chromosomes• All reproductive cells (sperm and egg);

called gametes(sex cells) • Represented by 1n

A haploid cell has the possibility of joining together with another haploid cell to form a diploid cell. (fertilization)

Part 2: Cell Cycle

Binary fission: division of a prokaryotic cell in two offspring cells

Three general stages• Copy DNA• Grow• Divide

Two types in eukaryotes Mitosis

• Results in two cells with genetic material identical to the original cell – used for: repair, growth, and asexual reproduction

• Meiosis

• Reduces the chromosome number by half and the genetic material is not the same

• Produces gametes which are sex cells• Part of sexual reproduction

The gametes are haploid cells which retain the ability to join together and form diploid cells.

Two major phases of the cell are interphase and cell division

Interphase is the time between divisions

Cell division is the division of the nucleus (mitosis) and the cytoplasm (cytokinesis)

Divided into three sub-phases

G1: where the cell matures S: DNA is replicated G2: Cell prepares for

division

*Cells do not divide forever* G0: cells have exited the

cell cycle and do not copy DNA or divide any more

Division of the nucleus; called the M phase

It is divided into four different phases• Prophase• Metaphase• Anaphase• Telophase

Shortening and tightening of DNA into chromosomes

The nuclear membrane and nucleolus disappear

Centrosomes appear and migrate toward the poles of the cell. In animal cells, the centrosomes contain centrioles.

Spindle fibers begin to radiate form the centrosomes • Kinetochore fibers • Polar fibers

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Chromosomes are easier to identify - can easily see the X shape.

Kinetochore fibers move the chromosomes to the center.

Once there the chromosomes are held in place.

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The chromatids separate and move centromere first to opposite poles

Once the chromatids separate they are considered to be individual chromosomes

Once the chromosomes reach the poles of the cell the spindle fibers disassemble

The chromosome returns to its uncoiled state

Nuclear membrane and a nucleolus forms in each cell

During telophase the cytoplasm begins to divide

Animals• Cleavage Furrow:

pinching inward of the membrane midway of the poles

Plants• Cell Plate: Vesicles

formed by the Golgi apparatus fuse midway of the dividing cell

The end result of mitosis is two identical daughter cells.

The cells will go back to interphase to grow and develop into full cells.

Cell growth (G1 ) checkpoint: the cell determines if it is ready to start the process of division

DNA synthesis (G2) checkpoint: check DNA synthesis

Mitosis checkpoint: check if mitosis proceeded correctly

When control is lost it can lead to cancer

Chapter 8Part 3: Meiosis and

Reproduction

Meiosis• Reduces the

chromosome number by half and the genetic material is not the same

• Produces gametes which are sex cells

• Part of sexual reproduction The gametes are

haploid cells which retain the ability to join together and form diploid cells.

Very similar to mitosis but produces haploid cells instead through 2 divisions: Meiosis I and Meiosis II

None of the cells have the same genetic information

All of the aspects of prophase that occur in mitosis occur here as well

Synapsis: pairing of homologous chromosomes

Tetrad: the pair formed in synapsis

Crossing-over: portions of the chromosomes break off and exchange with homologue

Genetic Recombination: new genetic material is made

Metaphase I• The tetrads line up in the middle

of the cell Anaphase I

• Here the homologous chromosomes separate and go toward opposite poles

• Since they randomly lined up in metaphase, they now randomly separate. This process is called independent assortment.

• Independent Assortment: the random separation of homologues

Telophase I and Cytokinesis• Here the cell will split into

two new cells• The end result is two cells

that are haploid cells.• Each cell is now considered

haploid cells, even though they have two copies of that chromosome. This is due to the fact that it no longer has a homologue.

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Occurs on the two cells formed during meiosis I Same procedure as mitosis End result of meiosis II is four new cells containing half the number of

chromosomes of the original cell **Some cells will start meiosis after the nuclear membrane completely

reforms; others start at the end of meiosis I

Sometimes errors can occur in meiosis

Whether the homologous chromosomes fail to separate in anaphase I or the sister chromatids fail to separate in anaphase II, nondisjunction has occurred.

This will lead to one or more sex cells that have too many chromosomes and one or more sex cells that are missing a chromosome.

The result is a genetic disorder.

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Meiosis occurs only in the reproductive organs in animals

Spermatogenesis• Each haploid cell called a

spermatid is form; spermatids develop into sperm cells

Oogenesis• In cytokinesis I and II the

cytoplasm does not split evenly• One egg (ovum) developed and

three polar bodies• The polar bodies will eventually

degenerate

Requires 1 parent - produces identical offspring

Types• Mitosis• Budding• Parthenogensis• Fragmentation

Benefits• Quick• Produce many offspring at one time• No energy wasted on finding a mate

Cons• No genetic variation – could lead to

the extinction of a species.

Requires 2 parents – leads to genetically different offspring.

Benefits• Offspring are genetically different

than each other and their parents*** - This allows a species to adapt to rapidly changing conditions.

Cons• Must find a mate• Expend energy in producing

gametes that may not be fertilized

*** With the exception of identical twins!***