Cell ReproductionCell Reproduction

Chromosome Structure Chromosome Structure Review Review

Except for the gametes, humans have Except for the gametes, humans have 46 chromosomes (23 pairs) in the 46 chromosomes (23 pairs) in the nucleus of every cell.nucleus of every cell.

Chromosomes are long strands of DNA Chromosomes are long strands of DNA (genetic code).(genetic code).

When chromosomes are uncoiled, they When chromosomes are uncoiled, they are called are called chromatinchromatin..

When chromosomes are coiled, they When chromosomes are coiled, they look like a “x”.look like a “x”.

Chromosome Structure Chromosome Structure Review Review

Centromere- holds 2 chromatids together

Chromatids- Each half of a chromosome

Each chromatid is a double helix (twisted ladder)

Cells with different numbers of Cells with different numbers of chromosomeschromosomes

Diploid (somatic cell) Diploid (somatic cell) – A cell consisting of – A cell consisting of homologous chromosomes . In humans, this homologous chromosomes . In humans, this cell has 46 chromosomes. One cell has 46 chromosomes. One chromosome of a pair came from the chromosome of a pair came from the mother and one from the father. All cells in mother and one from the father. All cells in the human body are diploid the human body are diploid except sex except sex cellscells..

Haploid (gamete) Haploid (gamete) – A cell that does not – A cell that does not contain chromosome pairs. The contain chromosome pairs. The sperm and and egg are haploid and, in humans, have 23 egg are haploid and, in humans, have 23 chromosomes. chromosomes.

Chromosome ShorthandChromosome Shorthand

n = # of unique chromosomes (haploid)n = # of unique chromosomes (haploid) 2n = # of chromosomes in pairs (diploid)2n = # of chromosomes in pairs (diploid)

XXxx XX

xx HomologousPair

n=4 Haploid cell

2n=8 Diploid cell

XX

x

x

Cell Cycle- Series of events for cells

Interphase is the time between cell division. This is when the cell grows and replication occurs (chromatids are copied). During interphase, DNA is uncoiled (chromatin).

Mitosis/Meiosis is the division of the cell’s nucleus (chromosomes).

Cytokinesis is division of the cell’s cytoplasm and membrane. This is when the cell physically splits in half.

 

Mitosis or Meiosis

Cytokinesis

 

Interphase

MITOSIS Mitosis results in new cells with genetic material

identical to that of the original cell. This process is the reason for human growth.

Mitosis occurs in all cells of the body except the sex cells (egg and sperm cells). Sex cells undergo a different process called meiosis.

Mitosis has 4 phases: Prophase, Metaphase, Anaphase and Telophase.

PROPHASE DNA supercoils (goes

from chromatin to chromosomes)

Nuclear membrane breaks down

Nucleolus breaks down Mitotic spindle forms

from the centrosomes (containing 2 centrioles)

METAPHASE

Chromosomes line up in single file at the center of the cell.

The chromosomes (at the centromere) are held in place by the mitotic spindle.

ANAPHASE The chromatids of

each chromosome separate and move toward opposite poles of the cell.

The spindle pulls the chromatids apart at their centromere.

TELOPHASE (opposite of Prophase)

Mitotic spindle breaks down

Chromosomes uncoil (become chromatin)

Nuclear envelopes reform

Nucleolus reappears within each envelope

CYTOKINESISCYTOKINESIS Cytokinesis occurs differently in Cytokinesis occurs differently in

animal and plant cells.animal and plant cells. In animal cells, the cell membrane In animal cells, the cell membrane

pinches in until it eventually splits pinches in until it eventually splits the cell into two. the cell into two.

This pinching in is called a This pinching in is called a cleavage cleavage furrow.furrow.

CYTOKINESISCYTOKINESIS In plant cells, cytokinesis occurs In plant cells, cytokinesis occurs

when a when a cell platecell plate forms and splits the forms and splits the cell into two.cell into two.

The cell plate starts to form in the The cell plate starts to form in the center and works its way outward center and works its way outward until it reaches the cell wall.until it reaches the cell wall.

Mitosis and Cytokiinesis Mitosis and Cytokiinesis PracticePractice

Each student kit needs:Each student kit needs:– one 8 foot orange string cut in ½one 8 foot orange string cut in ½– One 5 foot black string cut in ½One 5 foot black string cut in ½– 1 clear spoon and fork1 clear spoon and fork– 1 white spoon and fork1 white spoon and fork– 2 pom-poms2 pom-poms– 2 paper clips2 paper clips– 8 coffee stirrers8 coffee stirrers

What is the cell cycle What is the cell cycle phase? (IPMATC)phase? (IPMATC)

What is the cell cycle What is the cell cycle phase? (IPMATC)phase? (IPMATC)

What is the cell cycle What is the cell cycle phase? (IPMATC)phase? (IPMATC)

What is the cell cycle What is the cell cycle phase? (IPMATC)phase? (IPMATC)

What is the cell cycle What is the cell cycle phase? (IPMATC)phase? (IPMATC)

What is the cell cycle What is the cell cycle phase? (IPMATC)phase? (IPMATC)

MeiosisMeiosis A type of cell division in which the A type of cell division in which the

chromosome # is reduced by half to chromosome # is reduced by half to produce haploid cells.produce haploid cells.

This produces gametes (sex cells). This produces gametes (sex cells). Meiosis has the same phases as mitosis; Meiosis has the same phases as mitosis;

however, it goes through 2 rounds of however, it goes through 2 rounds of these phases. The phases of meiosis are these phases. The phases of meiosis are Prophase I/IIProphase I/II, , Metaphase I/IIMetaphase I/II, , Anaphase Anaphase I/III/II and and Telophase I/II.Telophase I/II.

PROPHASE IPROPHASE I Nuclear membrane breaks downNuclear membrane breaks down Nucleolus breaks downNucleolus breaks down Mitotic spindle forms from the centrosomesMitotic spindle forms from the centrosomes Chromatin coils to become chromosomesChromatin coils to become chromosomes Homologous chromosomes position Homologous chromosomes position

themselves next to each other- This is called themselves next to each other- This is called synapsissynapsis..

Crossing overCrossing over occurs- This is when occurs- This is when homologous chromosomes “swap” pieces of homologous chromosomes “swap” pieces of DNA with each other.DNA with each other.

METAPHASE IMETAPHASE I

Homologous pairs line up along the Homologous pairs line up along the midline of the cell. midline of the cell.

ANAPHASE IANAPHASE I Homologous chromosomes move Homologous chromosomes move

away from each other toward away from each other toward opposite poles of the cell.opposite poles of the cell.

TELOPHASE ITELOPHASE I

Nuclear membrane forms around each Nuclear membrane forms around each set of chromosomesset of chromosomes

Spindle breaks downSpindle breaks down Chromosomes Chromosomes do not do not uncoil and uncoil and

nucleoluses do not form because there nucleoluses do not form because there is a second round of nuclear division.is a second round of nuclear division.

This is followed by Cytokinesis I which This is followed by Cytokinesis I which produces 2 haploid cells.produces 2 haploid cells.

PROPHASE IIPROPHASE II

Nuclear membrane breaks downNuclear membrane breaks down Spindle formsSpindle forms

METAPHASE IIMETAPHASE II

Chromosomes line up in single file Chromosomes line up in single file along the midline of the cell.along the midline of the cell.

ANAPHASE IIANAPHASE II

Chromatids of chromosomes Chromatids of chromosomes separate and move to opposite poles separate and move to opposite poles of the cell.of the cell.

TELOPHASE IITELOPHASE II Chromosomes uncoil to become Chromosomes uncoil to become

chromatin.chromatin. Nuclear membranes form around each Nuclear membranes form around each

set of chromosomesset of chromosomes Nucleoluses form in each nuclear Nucleoluses form in each nuclear

membrane.membrane. Spindle breaks down.Spindle breaks down. This is followed by Cytokinesis II which This is followed by Cytokinesis II which

produces 4 haploid cells.produces 4 haploid cells.

Differences between mitosis Differences between mitosis and meiosisand meiosis

MitosisMitosis– Metaphase- Metaphase-

chromosomes are chromosomes are in single filein single file

– 2 product cells 2 product cells (diploid)(diploid)

– Somatic cells (non-Somatic cells (non-sex) producedsex) produced

– 4 phases (PMAT)4 phases (PMAT)

MeiosisMeiosis– Metaphase I Metaphase I

chromosomes are chromosomes are aligned as pairsaligned as pairs

– 4 product cells (haploid)4 product cells (haploid)– Sex cells (gametes) Sex cells (gametes)

producedproduced– Synapsis and crossing Synapsis and crossing

over occurs during over occurs during Prophase IProphase I

– 8 phases (PMAT 1 and 8 phases (PMAT 1 and 2)2)

What if meiosis yields sex What if meiosis yields sex cells with < or >23 cells with < or >23

chromosomes?chromosomes? Down SyndromeDown Syndrome Turner SyndromeTurner Syndrome Klinefelter SyndromeKlinefelter Syndrome