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Cell Division

Biology 30 Jon Paul Cooper

Cell Division I) Introduction

Cell Division I) Introduction n  nucleic acids are biological chemicals that

direct the growth and development of every organism. q  there are two types:

n  RNA (ribonucleic acid) n  DNA (deoxyribonucleic acid)


q  there are two types: n  RNA (ribonucleic acid) n  DNA (deoxyribonucleic acid)

q  DNA is the main component of genes in all cells n  each gene contains instructions for making RNA

q  RNA contains instructions for making proteins. q  proteins make up the structures of a cell and controls how it

functions.


q  RNA contains instructions for making proteins. q  proteins make up the structures of a cell and controls how

it functions. q  the majority of organism have no true nucleus

n  we call these organisms “prokaryotes” “pro” meaning before “karyon” meaning nucleus

n  the prokaryotes are divided into two domains: q  Bacteria q  Archaea

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n  we call these organisms “prokaryotes” “pro” meaning before “karyon” meaning nucleus

n  the proakaryotes are divided into two domains: q  Bacteria q  Archaea

n  organisms with a true nucleus are called eukaryotes “eu” meaning true “karyon” meaning nucleus q  eukaryotic cells have organelles that are specialized to

perform tasks much like cells of the human body are differentiated to perform tasks.

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Cell Division Activity

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Cell Division II) The Cell Cycle

Cell Division II) The Cell Cycle A) Introduction “growth comes about by the addition of new cells, not

the ever increasing size of just one cell” n  as cells grow in size the volume of its cytoplasm increases at

a faster rate than the surface area of plasma membrane q  the cell absorbs nutrients and excretes wastes through its

plasma membrane. q  if the cell continues to grow the plasma membrane will be

too small to meet the cells metabolic needs (cell can only be a certain maximum size)


q  the cell absorbs nutrients and excretes wastes through its plasma membrane. q  if the cell continues to grow the plasma membrane will be too small to meet

the cells metabolic needs (cell can only be a certain maximum size)

q  remember that cells need to keep a large surface area to volume ratio

Cell Division II) The Cell Cycle B) Cell Division and the Cell Cycle n  the life cycle of the cell is called the cell cycle. n  body cells are called somatic cells (all cells other than

gametes) q  somatic cells have varying cell cycles.

ex. blood and skin cells are replaced frequently nerve cells divide infrequently or not at all

n  a single cell cycle is defined as the sequence of events from one cell division to the next.


q  somatic cells have varying cell cycles. ex. blood and skin cells are replaced frequently nerve cells divide infrequently or not at all

n  a single cell cycle is defined as the sequence of events from one cell division to the next.

n  the central feature of the cell cycle is the way that genetic material is duplicated and then passed from the original cell (the parent cell) to each new cell (daughter cell) q  the process is possible because of the highly organized

genetic material within the cell.

Cell Division II) The Cell Cycle n  the central feature of the cell cycle is the way that genetic material is duplicated and

then passed from the original cell (the parent cell) to each new cell (daughter cell) q  the process is possible because of the highly organized genetic material within

the cell.

n  the genetic information of a cell is contained in the DNA. q  a chromosome

n  is a length of DNA and its associated proteins. n  is found in the nucleus.

q  there is about 3 meters of DNA in a single human cell. n  the diameter of a nucleus is only about 5 µm

(this like stuffing 150 m of string into a lunch box)


q  there is about 3 meters of DNA in a single human cell. n  the diameter of a nucleus is only about 5 µm

(this like stuffing 150 m of string into a lunch box)

q  a highly organized arrangement of proteins, called histones, and DNA compact the genetic material inside the nucleus. n  for the majority of a cell’s life genetic material appears as a mass of

long, intertwined strands known as chromatin.


n  for the majority of a cell’s life genetic material appears as a mass of long, intertwined strands known as chromatin.

n  as genetic material is reorganized during the process of cellular division, the threads of chromatin condense and become distinct chromosomes. q  the “pinched in” region in the

chromosome is a specialized region called a centromere.

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n  as genetic material is reorganized during the process of cellular division, the threads of chromatin condense and become distinct chromosomes. q  the “pinched in” region in the

chromosome is a specialized region called a centromere.


n  the number of individual chromosome numbers varies from species to species. q  human somatic cells have 46 chromosomes

n  these 46 chromosomes can be organized into 22 pairs of homologous (similar in appearance) chromosomes

n  each somatic cell has two sex chromosomes xx ~ female (homologous pair) xy ~ male (pair)

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n  each somatic cell has two sex chromosomes xx ~ female (homologous pair) xy ~ male (pair)

q  homologous chromosomes n  carry the same genes at the same location (locus)

(genes are areas of DNA that contain specific genetic information)

n  not identical to each other. q  they carry different forms, or alleles, of the same gene

Cell Division II) The Cell Cycle q  homologous chromosomes

n  carry the same genes at the same location (locus) (genes are areas of DNA that contain specific genetic information)

n  not identical to each other. q  they carry different forms, or alleles, of the same gene

q  a cell that contains pairs of homologous chromosomes is said to be diploid (Greek for “double”) n  the diploid number in humans is 46 or 23 pair.

q  a cell that contains unpaired chromosomes is said to be haploid (Greek for “single”) n  human gametes are haploid.

Cell Division II) The Cell Cycle q  a cell that contains unpaired chromosomes is said to be haploid (Greek for “single”)

n  human gametes are haploid.

n  diploid human cells are described as 2n=46 (“2n” meaning diploid)

n  haploid human cells are described as n = 23 (“n” meaning haploid) q  in corn plants n = 10 q  in fruit flies n = 4 q  In the Ophioglossum fern upto 2n = 1400 q  in a hermit crab 2n = 254


q  in corn plants n = 10 q  in fruit lies n = 4 q  In the Ophioglossum fern upto 2n = 1400 q  in a hermit crab 2n = 254

q  some organisms are polypoid n  have sets of more than two homologous chromosomes.

q  some plants are tetraploid (4n), triploid (3n) and even octoploid (8n)

q  the particular set of chromosomes that an individual has is called the karyotype. n  the human karyotype is made up of 22 pairs of autosomes

(non sex chromosomes) and one pair of sex chromosomes.


B) Stages of The Cell Cycle


B) Stages of the Cell Cycle n  the cell cycle takes place in phases that occur one after the other

without stopping. n  the phases of the cell cycle:

q  S phase q  G2 phase q  Mitosis and Cytokinesis q  G1 phase

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Cell Division II) The Cell Cycle n  the phases of the cell cycle:

q  S phase q  G2 phase q  Mitosis and Cytokinesis q  G1 phase

n  the cell cycle can be divided into two parts q  Division Phase

n  the components of the cytoplasm and the nucleus of the parent cell are divided to give rise to two identical daughter cells. q  mitosis is the segregation of the copied

material q  cytokinesis is the splitting of the parent

cell into two daughter cells. q  small part of the cell cycle


q  cytokinesis is the spliltting of the parent cell into two daughter cells. q  small part of the cell cycle

q  Interphase n  encompasses the majority of the cell cycle

q  G1 Phase §  first called the Gap 1 phase because early on no one knew what was

happening. §  now call Growth 1 phase because of the rapid growth that occurs

during it. q  S Phase

§  synthesis phase §  phase where DNA is replicated

~ two identical chromosomes, called sister chromatids are joined at the centromere.


q  S Phase §  synthesis phase §  phase where DNA is replicated

~ two identical chromosomes, called sister chromatids are joined at the centromere.

q  G2 Phase §  Gap 2 or Growth 2 phase §  time for the cell to rebuild

its reserves of energy and make proteins for cell division


C) Mitosis


C) Mitosis n  there are four main stages to mitosis

q  Prophase q  Metaphase q  Anaphase q  Telophase q  Cytokinesis (splitting of the cell)

Cell Division II) The Cell Cycle n  Prophase

q  the first phase of mitosis q  chromosomes become visible q  centrioles migrate to opposite poles of the cell

n  centrioles are small protein bodies found in the cytoplasm of animal cells that provides a site for spindle fibers to attach to.

n  spindle fibres are protein structures that guide the movement of chromosomes during cell division.

n  collectively centrioles and spindle fibres make up the spindle apparatus.


n  spindle fibres are protein structures that guide the movement of chromosomes during cell division.

n  collectively centrioles and spindle fibres make up the spindle apparatus.

n  most plant cells lack centrioles but have spindle fibres q  the centromere joining two chromatids anchor the

chromosomes to the spindle fibers. q  nuclear membrane appears to fade.


q  the centromere joining two chromatids anchor the chromosomes to the spindle fibers.

q  nuclear membrane appears to fade.

n  Metaphase q  Second phase of mitosis q  Chromosomes composed of sister chromatids move toward

the centre of the cell (the equatorial plate) q  Chromosomes are dark filaments attached to spindle fibers

(most visible at this stage) q  Chromatids can become intertwined


q  Chromosomes are dark filaments attached to spindle fibers (most visible at this stage)

q  Chromatids can become intertwined

n  Anaphase q  Third phase of mitosis q  The centromeres divide

n  The sister chromatids, now called chromosomes, move to opposite poles.

q  The same number and same type of chromosomes will be found at each pole.


n  The sister chromatids, now called chromosomes, move to opposite poles. q  The same number and same type of chromosomes will be found at each pole.

n  Telophase q  the last phase of mitosis q  the chromosomes reach the opposite poles of the cell. q  spindle fibers dissolve and a nuclear membrane forms

around each mass of chromatin


q  The chromosomes reach the opposite poles of the cell and length. q  Spindle fibers dissolve and a nuclear membrane forms around each mass of

chromatin

n  Cytokinesis q  the division of the cytoplasm

n  in an animal cell a furrow develops, pinching off the cell into two pairs.

n  in plant cells a cell plate will develop into a new cell wall.


q  The division of the cytoplasm n  In an animal cell a furrow develops, pinching off the cell into two pairs. n  In plant cells a cell plate will develop into a new cell wall.

n  The Cell Clock q  cells have a biological clock that regulates the

number of cell divisions Example) Heart Cells n  normally can undergo mitosis approximately 50 times. n  if you freeze the cells in liquid nitrogen after 10 division

they will divide 40 more times when thawed. q  this proves that there is some sort of “cell clock”


n  normally can undergo mitosis approximately 50 times. n  if you cytogenetically free the cells after 10 division they will divide 40

more times when thawed. q  this proves that there is some sort of “cell clock”

q  usually more specialized cells (neurons, excretory) divide less than nonspeciallized (skin, stomach lining)

q  two types of cells divide endlessly n  sperm producing spermatogonia n  cancer cells

q  the biological clock is turned on after cells differentiate.


D) Cloning

Cell Division II) The Cell Cycle Cloning 411 n  cellular differentiation

q  is the process by which a less specialized cell becomes a more specialized cell type.

q  occurs numerous times as the organism changes from a single zygote to a complex system of tissues and cell types.

q  a common process in adults as well: adult stem cells divide and create fully-differentiated daughter cells during tissue repair and during normal cell turnover.


q  occurs numerous times as the organism changes from a single zygote to a complex system of tissues and cell types.

q  a common process in adults as well: adult stem cells divide and create fully-differentiated daughter cells during tissue repair and during normal cell turnover.

q  causes a cells size, shape, polarity, metabolic activity, and responsiveness to signals to change dramatically.

q  these changes are largely due to highly-controlled modifications in gene expression. n  different cells can have very different physical

characteristics despite having the same genome.


q  these changes are largely due to highly-controlled modifications in gene expression. n  different cells can have very different physical characteristics despite having

the same genome.

n  a cell that is able to differentiate into many cell types is known as pluripotent. q  called stem cells in animals q  called meristematic cells in higher plants

Cell Division II) The Cell Cycle n  a cell that is able to differentiate into many cell types is known as pluripotent.

q  called stem cells in animals q  called meristematic cells in higher plants.

q  a cell that is able to differentiate into all cell types is known as totipotent. n  in mammals, only the zygote and early embryonic cells

are totipotent, while in plants (and in animals), many differentiated cells can become totipotent with simple laboratory techniques.


What is Cloning? q  cloning is the process of forming identical offspring from a

single cell or tissue of a parent organism. n  both the clone and the parent have identical or near identical DNA

(random mutations occur) n  does not result in variation of traits

q  considered a form of asexual reproduction n  clones occur naturally

example) q  Hydra undergoing mitosis during the process of budding


example) n  Hydra undergoing mitosis

during the process of budding n  Runner of a strawberry plant n  Monozygotic twins (zygote

undergoes mitosis and splits into two)


n  Hydra undergoing mitosis during the process of budding n  Runner of a strawberry plant n  Monozygotic twins (zygote undergoes mitosis and splits into two)

n  Plant Cloning q  In 1958 Fredrick Stewart produced a carrot plant from a

single carrot cell n  now cloning is widespread in the agriculture/horticulture

industries. q  it is desirable (profitable) to have plants of predictable

characteristics §  Easy to clone plants: carrots, tobacco, lettuce §  Hard to clone plants: grasses, legumes.


§  Easy to clone plants: carrots, tobacco, lettuce §  Hard to clone plants: grasses, legumes.

n  Animal Cloning q  Robert Biggs and Thomas King

n  investigated nuclear transplants in frogs. n  first to clone a frog.

Cell Division II) The Cell Cycle n  Animal Cloning

q  Robert Biggs and Thomas King n  investigated nuclear transplants in frogs. n  first to clone a frog

n  the cloning of the sheep “Dolly” by Dr. Ian Wilmut’s team was the first to clone an animal using adult cells. q  the nucleus of an udder cell of an adult sheep was placed in

the enucleated egg cell from another sheep. n  the egg developed in a Petri dish until an early embryo

stage. q  then the egg was placed into the womb of another

sheep.


n  the egg developed in a Petri dish until an ealry embyro stage.

q  then the egg was placed into the womb of another sheep. q  DNA donor: adult Finn Dorsett Sheep q  Egg donor: Poll Dorsett Sheep q  Womb provider: a third sheep q  Clone: Dolly was a clone of the adult Finn Dorsett Sheep


E) Cell Aging

Cell Division II) The Cell Cycle E) Cell Aging n  Telomeres

q  are caps at the ends of chromosomes. q  they reduce in length each time a cell

undergoes the cell cycle q  have a role in cell aging and cancer cells. q  the length of telomeres is affected by the

enzyme telomerase.

E) Cell Aging


q  have a role in cell aging and cancer cells. q  the length of telomeres is affected by the enzyme

telomerase.

q  as cells go through the cell cycle their telomeres become shorter. n  eventually the telomeres become very short and

the cell stops going through the cell cycle and dies. q  telomerase is an enzyme that keeps the

telomerese long but is only found at limited levels in somatic cells. §  embyronic stem cells have a high level of

telomerase. q  telomere length acts as a biological clock.

E) Cell Aging


q  telomerase is an enzyme that keeps the telomerese long but is only found at limited levels in somatic cells. §  embyronic stem cells have a high level of

telomerase. q  telomere length acts as a biological clock.

q  the case of “Dolly” the prematurely aging sheep. n  Dolly was cloned using an adult nucleus

with telomeres that had already began to shorten.

n  Dolly developed arthritis and died of a lung disease at only half her life expectancy.

E) Cell Aging


n  Dolly was cloned using an adult nucleus with telomeres that had already began to shorten.

n  Dolly developed arthritis and died of a lung disease at only half her life expectancy.

q  the case of Cancer n  cancer cells never seem to lose their

ability to divide. q  the telomeres of cancer cells do not

shorten. q  telomerase is reactivated in cancer

cells allowing the cancer cells to maintain telomere length and keep on dividing.

E) Cell Aging


E) Cell Aging

Somatic cells Telomerase is inactive Telomeres shorten

Abnormal cells ignore warning to stop dividing.

Telomerase is inactive

Telomere shorten

Immortalized somatic cells and tumor cells.

Telomerase is active.

Telomeres are maintained.

Crisis. Most cells die.

Threshold to senescence

Most cells stop dividing.

Cell Division III) Meiosis

A) Introduction

A) Introduction

Cell Division III) Meiosis Meiosis n  a type of cell division n  results in the formation of sex cells, or gametes. n  in humans it occurs in the testis and ovaries. n  involves two stages of cell division

q  both have similarities to the phases in mitosis

n  the chromosome number of the daughter cells is half that of the parent cell (haploid number or n)

A) Introduction

Cell Division III) Meiosis n  involves two stages of cell division

q  both have similarities to the phases in mitosis n  the chromosome number of the daughter cells is half that of the parent cell (haploid

number or n)

n  each parent provides half the genetic information to their offspring. q  each of the 23 chromosomes you receive from your father is

matched up with 23 chromosomes from your mother. n  the paired chromosomes are called homologous

chromosomes. q  there are 22 pairs of homologous chromosomes q  the 23rd pair are the sex chromosomes and are only

partially homologous.

A) Introduction


n  the paired chromosomes are called homologous chromosomes. q  there are 23 pairs of homologous chromosoms q  the 23rd pair are the sex chromosomes and are only partially

homologous.

n  during fertilization, a haploid (n = 23) sperm cell unites with a haploid (n = 23) egg cell to produce a diploid (2n = 46) zygote. q  the zygote will begin dividing by mitosis and become a

multicellular organism.

A) Introduction

Cell Division III) Meiosis B) Stages

B) Stages


Cell Division III) Meiosis n  meiosis

q  involves two nuclear division. n  Meiosis I n  Meiosis II

q  produces four haploid cells. n  meiosis I is called reduction division because the diploid (2n)

chromosome number is reduced to the haploid (n) chromosome number

n  meiosis II is marked by the separation of the two chromatids. n  DNA synthesis occurs prior to the two nuclear divisions.*

B) Stages

Cell Division III) Meiosis n  meiosis II is marked by the separation of the two chromatids. n  DNA synthesis occurs prior to the two nuclear divisions.

Meiosis I n  Stages:

q  Prophase I q  Metaphase I q  Anaphase I q  Telophase I

n  Prophase I q  nuclear membrane begins to dissolve q  centriole splits, parts move to opposite poles and spindle fibres form.

B) Stages

B) Stages

Cell Division III) Meiosis n  Prophase I

q  nuclear membrane begins to dissolve q  centriole splits, parts move to opposite poles and spindle fibres form. q  chromosomes come together in homologous pairs.

n  each chromosome of the pair is a homologue and is composed of a pair of sister chromatids. q  the whole structure is referred to as a tetrad (because there are four

chromatids)


n  each chromosome of the pair is a homologue and is composed of a pair of sister chromatids. q  the whole structure is referred to as a tetrad (because there is four

chromatids)

q  each pair of homologous chromosomes align side by side (non-sister chromatid to another) n  this aligning is called synapsis. n  as the chromosomes synapse they often intertwine

q  the intertwined chromatids from different homologous break and exchange segments in a process called crossing over.

B) Stages


n  this aligning is called synapsis. n  as the chromosomes synapse they often intertwine


B) Stages


n  this aligning is called synapsis. n  as the chromosomes synapse they often intertwine


q  DNA information is exchanged during the crossing over event. §  promotes variation within the species.

B) Stages

Cell Division III) Meiosis n  Metaphase I

q  homologous chromosomes attach themselves to the spindle fibres and line up along the equatorial plate

B) Stages


B) Stages

Cell Division III) Meiosis n  Metaphase I

q  homologous chromosomes attach themselves to the spindle fibres and line up along the equatorial plate

n  Anaphase I q  the homologous chromosomes move toward

opposite poles. n  this is called segregation

q  reduction division occurs n  One member of each homologous pair will

be found in each of the new cells.

B) Stages


n  this is called segregation q  reduction division occurs

n  One member of each homologous pair will be found in each of the new cells.

n  Telophase I q  a membrane begins to form around each nucleus.

n  the chromosomes in the nuclei are not identical because each of the daughter nuclei contains one member of the homologous chromosome pair. q  homologous chromosomes are similar but

not identical.

B) Stages


B) Stages


n  the chromosomes in the nuclei are not identical because each of the daughter nuclei contains one member of the homologous chromosome pair. q  homologous chromosomes are similar but not identical

Meiosis II n  Stages:

q  Prophase II q  Metaphase II q  Anaphase II q  Telophase II

n  the stages occur at approximately the same time for each of the haploid daughter cells.

n  there is no replication of chromosomes prior to meiosis II.

B) Stages

Cell Division III) Meiosis n  the stages occur at approximately the same time for each of the

haploid daughter cells. n  there is no replication of chromosomes prior to meiosis II.

n  Prophase II q  the nuclear membrane dissolves and spindle

fibres form.

B) Stages

Cell Division III) Meiosis n  Prophase II

q  the nuclear membrane dissolves and spindle fibres form.

n  Metaphase II q  arrangement of each chromosome,

each with two chromatids, along the equatorial plate. n  chromatids are held together by the

centromere

B) Stages


B) Stages


q  the nuclear membrane dissolves and spindle fibres form.

n  Metaphase II q  arrangement of each chromosome, each with two

chromatids, along the equatorial plate. n  chromatids are held together by the

centromere

n  Anaphase II q  breaking of the attachment between

the two chromatids. q  migration of chromatids (now called

chromosomes) to opposite poles.

B) Stages


q  the nuclear membrane dissolves and spindle fibres form. n  Metaphase II

q  arrangement of each chromosome, each with two chromatids, along the equatorial plate. n  chromatids are held together by the centromere

n  Anaphase II q  breaking of the attachment between the two chromatids. q  migration of chromatids (now called chromosomes) to opposite poles.

n  Telophase II q  second nuclear division is completed q  second division of cytoplasm occurs (cytokenesis) q  four haploid daughter cells are produced

B) Stages


B) Stages


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B) Stages


MITOSIS MEIOSIS

MEIOSIS I

Prophase I

Chiasma

Homologous chromosome pair

Chromosome replication

Parent cell

2n = 6

Chromosome replication

Replicated chromosome

Prophase

Metaphase Metaphase I

Anaphase I Telophase I

Haploid n = 3

Daughter cells of

meiosis I

Anaphase Telophase

2n 2n

Daughter cells of mitosis

n n n n

MEIOSIS II

Daughter cells of meiosis II

SUMMARY

Meiosis

Occurs during interphase before meiosis I begins

Two, each including prophase, metaphase, anaphase, and telophase

Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion

Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other

Produces gametes; reduces number of chromosomes by half and introduces genetic variability amoung the gametes

Mitosis

Occurs during interphase before mitosis begins

One, including prophase, metaphase, anahase, and telophase

Does not occur

Two, each diploid (2n) and genetically identical to the parent cell

Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction

Property

DNA replication

Number of divisions

Synapsis of homologous chromosomes

Number of daughter cells and genetic composition

Role in the animal body

B) Stages


B) Stages


Cell Division III) Meiosis C) Genetic

Recombination

Cell Division III) Meiosis Genetic Recombination n  the formation of new combinations of genes n  comes about by

q  independent assortment q  crossing over

C) Genetic Recombination

Cell Division III) Meiosis n  comes about by

q  independent assortment q  crossing over

n  Independent Assortment q  during metaphase I chromosome arrange in homologous pairs along the

equator of the cell. n  the chromosome of maternal origin is orientated toward one

pole of the cell while the chromosome of paternal origin is oriented towards the other pole

n  this orientation is “independent” of other homologous pairs n  it results in gametes having different combinations of parental

chromosomes.


Cell Division III) Meiosis n  Independent Assortment

q  during metaphase I chromosome arrange in homologous pairs along the equator of the cell. n  the chromosome of maternal origin is orientated toward one pole of the cell while the

chromosome of paternal origin is oriented towards the other pole n  this orientation is “independent” of other homologous pairs n  it results in gametes having different combinations of parental chromosomes.


Cell Division III) Meiosis n  Independent Assortment

q  during metaphase I chromosome arrange in homologous pairs along the equator of the cell. n  the chromosome of maternal origin is orientated toward one pole of the cell while the

chromosome of paternal origin is oriented towards the other pole n  this orientation is “independent” of other homologous pairs n  it results in gametes having different combinations of parental chromosomes.


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Cell Division III) Meiosis n  Crossing Over

q  occurs when chromosomes synapse, or pair up during prophase I.

q  Non-sister chromatids exchange pieces of chromosome. n  the section that is crossed over may contain hundreds or even

thousands of genes.

q  can create individual chromosomes with both maternal and paternal genes.

q  can occur at several points along the non-sister chromatids.


Cell Division III) Meiosis n  Crossing Over

q  occurs when chromosomes synapse, or pair up during prophase I. q  non-sister chromatids exchange pieces of chromosome.

n  the section that is crossed over may contain hundreds or even thousands of genes. q  can create individual chromosomes with both maternal and paternal genes. q  can occur at several points along the non-sister chromatids.


Cell Division III) Meiosis D) Gamete

Development

Cell Division III) Meiosis Gametogenesis n  the formation of sex cells during meiosis. n  both females and males follow the same process of meiosis to

develop gametes but there is differences in the final products. q  the cytoplasm of the female gamete does not divide equally

after each nuclear division. n  this results:

q  in one cell, called the ootid, receiving most of the cytoplasm.

q  three polar bodies that die and are absorbed by the body

D) Gamete Development


n  this results: q  in one cell, called the ootid, receiving most of the cytoplasm. q  three polar bodies that die and are absorbed by the body


Spermatogenesis n  the process starts with a diploid germ cell called a

spermatogonium. q  starting at puberty mitosis forms two spermatogonium

daughter cells. n  one cell replenishes the spermatogonia n  one cell develops into a primary spermatocyte

q  the primary spermatocyte undergoes meiosis I to form two secondary spermatocytes.

q  the secondary spermatocytes undergo meiosis II to form four spermatids.



q  the primary spermatocyte undergoes meiosis I to form two secondary spermatocytes.

q  the secondary spermatocytes undergo meiosis II to form four spermatids.

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Oogenesis n  oogenesis starts with the diploid germ cell called an oogonium.

q  each oogonium undergoes mitosis to form two primary oocytes.

q  three months after conception two million primary oocytes can be found in the ovaries arrested in prophase I awaiting puberty.

q  three months after conception two million primary oocytes can be found in the ovaries arrested in prophase I awaiting puberty.

q  every month after puberty one primary oocyte undergoes meiosis. n  unequal division of cytoplasm called asymmetrical

cytokinesis occurs. n  the cell that receives the most cytoplasm is called the

secondary oocyte, the other cell is called the first polar body. q  the first polar body may or may not go through a

second division to produce a pair of polar bodies.


n  the cell that receives the most cytoplasm is called the secondary oocyte, the other cell is called the first polar body. q  the first polar body may or may not go through a second division to

produce a pair of polar bodies.

q  when sperm penetrates the secondary oocyte it undergoes meiosis II. §  cytoplasm divides unequally again. §  the cell with the most cytoplasm becomes the

mature egg. §  the cell with the least cytoplasm becomes the

second polar body.



§  cytoplasm divides unequally again. §  the cell with the most cytoplasm becomes the mature egg. §  the cell with the least cytoplasm becomes the second polar body.

n  cool facts about oogenesis q  asymmetrical cytokinesis allows for one egg to have a large

amount of nutrients (cytoplasm) for the zygote to use prior to implantation

q  meiosis I and II is not continuous n  primary oocytes begin meiosis I before birth but stalls in

prophase I until puberty. n  secondary oocytes stalls at metaphase II until fertilization

occcurs. q  if fertilization does not occur meiosis II will not be

completed.




E) Abnormal Meiosis

Cell Division III) Meiosis Abnormal Meiosis n  nondisjunction occurs when two homologous chromosomes

fail to separate during meiosis or mitosis. q  one of the daughter cells will have too many chromosomes,

while another will have too few. q  the effects of nondisjunction are more devastating in the

production of gametes. n  nondisjunction occurs during anaphase I or anaphase II

E) Abnormal Meiosis


q  one of the daughter cells will have too many chromosomes, while another will have too few.

q  the effects of nondisjunction are more devastating in the production of gametes. n  nondisjunction occurs during anaphase I or anaphase II

n  nondisjunction in humans produces: q  gametes with 22 and 24 chromosomes.

n  if the gamete with 24 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 47 chromosomes is produced. q  the zygote will have three chromosomes rather than a

pair. §  this condition is referred to as trisomy.

E) Abnormal Meiosis


n  if the gamete with 24 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 47 chromosomes is produced. q  the zygote will have three chromosomes rather than a pair.

§  this condition is referred to as trisomy.

n  if the gamete with 22 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 45 chromosomes is produced. q  the zygote will have one chromosome rather than a pair

§  this condition is referred to as monosomy. n  once the cells of trisomic or monosomic zygotes begin to

divide, each cell of body will be one plus or one minus a chromosome.

E) Abnormal Meiosis


q  the zygote will have one chromosome rather than a pair §  this condition is referred to as monosomy.

n  once the cells of trisomic or monosomic zygotes begin to divide, each cell of body will be one plus or one minus a chromosome.

E) Abnormal Meiosis PRINT ME PRINT ME

Cell Division III) Meiosis Nondisjunction Disorders n  Male and Female Syndromes

q  Down Syndrome n  trisomy 21

q  Patau Syndrome n  trisomy 13

q  Edward Syndrome n  trisomy 18

E) Abnormal Meiosis


q  Down Syndrome n  trisomy 21

q  Patau Syndrome n  trisomy 13

q  Edward Syndrome n  trisomy 18

n  Gender Specific q  Turner Syndrome (female)

n  X0 q  Triplo-X Syndrome (female)

n  XXX or XXXX

E) Abnormal Meiosis

Cell Division III) Meiosis n  Gender Specific

q  Turner Syndrome (female) n  X0

q  Triplo-X Syndrome (female) n  XXX or XXXX

q  Klinefelter Syndrome (male) n  XXY or XXXY

q  Jacob’s Syndrome (male) n  XYY

E) Abnormal Meiosis


q  Klinefelter Syndrome (male) n  XXY or XXXY

q  Jacob’s Syndrome (male) n  XYY

n  the chances of nondisjunction disorder increases with age q  chances of having a child with Down’s Syndrome

n  conceiving between 20 and 24 years, 1 in 1490 n  conceiving at age 40, 1 in 106 n  conceiving at age 49, 1 in 11

E) Abnormal Meiosis



F) Karyotype

Cell Division III) Meiosis Karyotype n  a chart of chromosomes. n  obtained by mixing a small sample of tissue with a chemical that

stimulates mitotic division. q  division is the stopped during metaphase. q  chromosomes are stained q  a picture is taken and chromosomes are paired up with their

homologue. n  homologue chromosomes are similar in size, length,

centromere location and banding pattern. n  the are organized in decreasing size with the sex chromosome

placed at the end.

E) Karyotype PRINT ME PRINT ME PRINT ME


E) Karyotype


Normal Male

E) Karyotype


Jacobs Syndrome

E) Karyotype


Turner Syndrome

E) Karyotype


Down Syndrome

E) Karyotype


Cell Division IV) Reproductive

Strategies A) Introduction

Cell Division IV) Reproductive Strategies n  mitosis is a key mechanism in asexual reproduction n  meiosis is a key mechanism in sexual reproduction. n  the life cycle of many organisms involves both forms of cell

division

A) Introduction

Cell Division IV) Reproductive Strategies n  meiosis is a key mechanism in sexual reproduction. n  the life cycle of many organisms involves both forms of cell division

Reproduction in Prokaryotes n  bacteria, like human somatic cells, replicate their DNA and

transfer one complete copy into each of two daughter cells. q  unlike human cells bacteria have a single circular

chromosome and no nucleus. n  it does not undergo mitosis n  it reproduces by a form of cell division called binary

fission.

A) Introduction

PRINT ME

Cell Division IV) Reproductive Strategies

q  unlike human cells bacteria have a single circular chromosome and no nucleus. n  it does not undergo mitosis n  it reproduces by a form of cell division called binary

fission. q  bacteria can divide in as little as 20 minutes

n  each daughter cell can produce two new cells q  this is called exponential growth

§  allows for huge populations of identical bacterial (no diversity) to be produced quickly.

q  some bacteria can reproduce by bacterial conjugation.

A) Introduction


q  this is called exponential growth §  allows for huge populations of identical bacterial (no diversity) to be

produced quickly.

q  some bacteria can reproduce by bacterial conjugation. n  involves the transfer of genetic material from cell to cell contact via

a pilus.

A) Introduction


q  some bacteria can reproduce by bacterial conjugation. n  involves the transfer of genetic material from cell to

cell contact via a pilus.

q  conjugation: n  results in cells with new genetic

material n  occurs between non-identical bacterial

cells n  creates a single genetically unique

daughter that can undergo binary fission.

A) Introduction


n  results in cells with new genetic material n  occurs between non-identical bacterial cells n  creates a single genetically unique daughter that can undergo binary fission.

Asexual Reproduction n  Budding

q  a complete smaller version of the parent grows out of the parent’s body.

A) Introduction

Cell Division IV) Reproductive Strategies n  Budding

q  a complete smaller version of the parent grows out of the parent’s body.

n  Vegetative Reproduction q  creeping or running plants. q  once a new plant takes root the runners or stems disappear.

n  Fragmentation q  an entirely new plant is grown from a cutting or fragment of a parent

plant q  can occur in sea stars

A) Introduction

Cell Division IV) Reproductive Strategies n  Fragmentation

q  an entirely new plant is grown from a cutting or fragment of a parent plant q  can occur in sea stars

Parthenogenesis n  a form a asexual reproduction n  unfertilized egg develops into an adult.

q  example Bees n  Queen lays fertilized and unfertilized eggs

q  fertilized: develop into female worker bees q  unfertilized: develop into male drones.

A) Introduction


q  example Bees n  Queen lays fertilized and unfertilized eggs

q  fertilized: develop into female worker bees q  unfertilized: develop into male drones.

Spores n  a form of asexual reproduction, can be produced by meiosis n  a method to disperse offspring great distances

q  spores contain the genetic information and cytoplasm encased in a protective coating.

n  can be haploid or diploid n  can remain dormant until environment is suitable to support

development.

A) Introduction


Cell Division IV) Reproductive

Strategies B) Alternation of

Generations

Cell Division IV) Reproductive Strategies Alternation of Generations n  the life cycle of plants consists of two generations

q  a haploid generation q  a diploid generation

B) Alternation of Generations

Cell Division IV) Reproductive Strategies Alternation of Generations n  the life cycle of plants consists of two generations

q  a haploid generation q  a diploid generation

n  the diploid generation of the plant is called the sporophyte (spore making body) q  through meiosis the sporophyte produces one or more haploid

spores. n  each haploid spore grows into a plant body called a

gametophyte (gamete making body) q  gametophytes produce male and female gametes

n  the gametes fuse at fertilization and make another sporophyte



n  each haploid spore grows into a plant body called a gametophyte (gamete making body)

q  gametophytes produce male and female gametes n  the gametes fuse at fertilization and make another sporophyte

n  all plant life cycles include a sporophyte generation and gametophyte generation q  one generation is dominant over the other in different plant

groups. n  vascular plants (plants with a transport system and conducting

tubes) usually have a diploid sporophyte dominant generation n  non-vascular plants (like mosses) have a haploid gametophyte

dominant stage.



n  vascular plants (plants with a transport system and conducting tubes) usually have a diploid sporophyte dominant generation

n  non-vascular plants (like mosses) have a haploid gametophyte dominant stage.

Mosses n  the leafy green ground/tree hugging plant we normally

see mosses as is the gametophyte q  a certain times of year a stalk grows out of the greenage,

the stalk is the sporophyte and spores are released from its cap.

q  these spores fall to ground and develop into the gametophyte.



q  a certain times of year a stalk grows out of the greenage, the stalk is the sporophyte and spores are released from its cap.

q  these spores fall to ground and develop into the gametophyte.

q  structures within the gametophyte produce sperm and eggs. §  each fertilized egg will develop a new stalk.



Conifers n  in conifers like pine trees, the tree is the diploid sporophyte n  the gametophytes are microscopic structures within the

male and female cones that the tree produces. q  the female gametophyte develops from a specialized

structure at the top of each scale of the female cone (the larger cone) §  it stays within the cone

q  the male gametophyte develops from a structure found on the male cone (the smaller cone) §  it is released as pollen



q  the female gametophyte develops from a specialized structure at the top of each scale of the female cone (the larger cone) §  it stays within the cone

q  the male gametophyte develops from a structure found on the male cone (the smaller cone) §  it is released in the pollen

q  pollen is dispersed by the wind and if it reaches a female cone, sperm from the male gametophyte will grow and fertilize the egg within the female gametophyte.

q  the zygote forms a seed that is attached to the scale of the female cone.


Alternation of Sexual Cycles q  alternation of generations is only found in plants q  some animals can have life cycles that alternate between

asexually and sexual phases. Cnidarians (Jellyfish, Sea Anemones, and Corals)

n  these organisms have two distinct adult forms q  the non-motile polyp q  free swimming medusa


Cnidarians (Jellyfish, Sea Anemones, and Corals) n  these organisms have two distinct adult forms

q  the non-motile polyp q  free swimming medusa

n  in the jellyfish the medusa stage is dominant n  in sea anemones the polyp stage is dominaint



n  in the jellyfish the medusa stage is dominant n  in sea anemones the polyp stage is dominant

q  Obelia species of jellyfish n  has an asexual polyp stage and sexual medusa stage

Advantages to Sexual Reproduction q  generates diversity

n  creates a population more able to adapt to environmental changes

q  genetic diversity may reduce sibling competition for resources.

q  pairing and crossing over of chromosomes offers an opportunity to repair damaged chromosomes.


Advantages to Sexual Reproduction q  generates diversity

n  creates a population more able to adapt to environmental changes q  genetic diversity may reduce sibling competition for resources. q  pairing and crossing over of chromosomes offers an opportunity to repair

damaged chromosomes.

Advantages to Asexual Reproduction q  occurs quickly q  does not require a partner q  requires less energy q  ability to maximize surival by maintaining the generation

that is best suited for the environment.


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