Cell Reproduction

Cell Reproduction

Homework!• www.cellsalive.com• Complete the mitosis and meiosis sheets

Cells Division Introductory Video

The Chromosome

•During cell division the cell’s DNA is coiled compactly into a CHROMOSOME

•Each chromosome is a single DNA molecule

•The DNA wraps tightly around a protein called HISTONE (helps maintain the chromosome’s shape)

Breaking Down the Definitions1. Chromosome2. Histone3. Chromatid4. Centromere5. Chromatin6. Sex chromosome7. Autosome8. Homologous

chromosome9. Karyotype10. Diploid

11. Haploid12. Binary fission13. Mitosis14. Asexual reproduction15. Meiosis16. Gamete17. Interphase18. Cytokinesis19. Prophase20. Spindle fiber

21. Metaphase22. Anaphase23. Telophase24. Cell plate25. Synapsis26. Tetrad27. Crossing over28. genetic recombination29. Independent assortment30. Sexual reproduction

Anatomy of a Chromosome• Each half of a chromosome is

called a CHROMATID• Chromatids form as the DNA

copies itself before cell division• The 2 Chromatids are attached at

a point called a CENTROMERE• CHROMATIN=less tightly areas of

DNA between cell divisions

Chromosome Numbers• Every species has a certain number of

chromosomes in each cell.• Animal chromosomes are either:

• Sex Chromosomes—will determine the gender of an organism (X and Y)

• Autosomes—all of the other chromosomes

• Cells with 2 sets of Chromosomes are DIPLOID

• Cells with one set of chromosomes are HAPLOID (sex cells…half the number of chromosomes)

Chromosomes Clip• How many chromosomes does a potato have?

• How many chromosomes do Ferns have?

• After the video…in your own words why do different organisms have different numbers of chromosomes??

Cell Division (aka Cell Reproduction) in Prokaryotes•Most prokaryotes reproduce by BINARY FISSION

•2 identical cells are produced from one cell

•Draw this

Cell Division Eukaryotes• Two types of Cell Division

(Reproduction) in Eukaryotes!• Mitosis=new cells with

identical genetic material• Meiosis=reduces the number

of chromosomes by half for the purpose of eventual reproduction

Mitosis

Meiosis

The Cell Cycle•The CELL CYCLE is the repeating events of the life of a cell.

• Interphase is the period between cell divisions

How do little elephants grow up to be BIG elephants?

Three reasons why cells reproduce by asexual reproduction or MITOSIS:

1. Growth 2. Repair 3. Replacement

Mitosis Cycle

• Interphase• Prophase• Metaphase• Anaphase• Telophase & Cytokinesis

Interphase occurs before mitosis begins

• Chromosomes are copied (# doubles)• Chromosomes appear as threadlike coils (chromatin) at the

start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase

CELL MEMBRANENucleus

Cytoplasm

InterphaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Prophase 1st step in Mitosis

• Mitosis begins (cell begins to divide)• Centrioles (or poles) appear and begin to move to opposite

end of the cell. • Spindle fibers form between the poles.

CentriolesSister chromatids

Spindle fibers

ProphaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Spindle fibers

Centrioles

Metaphase 2nd step in Mitosis

•Chromatids (or pairs of chromosomes) attach to the spindle fibers.

Centrioles

Spindle fibers

MetaphaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Anaphase 3rd step in Mitosis

•Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell.

Centrioles

Spindle fibers

AnaphaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Telophase 4th step in Mitosis

• Two new nuclei form. • Chromosomes appear as chromatin (threads rather than

rods).• Mitosis ends.

NucleiNuclei

Chromatin

TelophaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Cytokinesisoccurs after mitosis

•Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes.

Animal Mitosis -- ReviewInterphase

Prophase

Metaphase

Anaphase

Telophase

Interphase

Plant Mitosis -- ReviewInterphase

Prophase

Metaphase

Anaphase

Telophase

Interphase

REMEMBER!InterphaseProphaseMetaphaseAnaphaseTelophaseCytokinesis

IPMATC

I P___ M___ A___ T___ C______

Label it!

Brainpop Mitosis

Mitosis in an Onion

Prophase

Metaphase

Anaphase

TELOPHASE and CYTOKINESIS

Stages of Mitosis Animation

It’s your turn! Identify the stages of mitosis…

Mitosis Dance Video

Onion Tips and Whitefish…

View 1 View 2 View 3 View 4 View 5

Whitefish

Onion

Meiosis KM 42

Meiosis – key differences from mitosis

• Meiosis reduces the number of chromosomes by half.• Daughter cells differ from parent, and each other.• Meiosis involves two divisions, Mitosis only one.• Meiosis I involves:

• Synapsis – homologous chromosomes pair up. Chiasmata form (crossing over of non-sister chromatids).

• In Metaphase I, homologous pairs line up at metaphase plate.• In Anaphase I, sister chromatids do NOT separate.• Overall, separation of homologous pairs of chromosomes, rather

than sister chromatids of individual chromosome.

Meiosis I (four phases)• Cell division that reduces the chromosome number

by one-half.

• four phases:a. prophase Ib. metaphase Ic. anaphase Id. telophase I

Meiosis• The form of cell division by which gametes (sperm or egg cells), with

half the number of chromosomes, are produced.

• Diploid (2n) haploid (n) n=# of chromosomes

• Meiosis is sexual reproduction.

• Two divisions (meiosis I and meiosis II).

Meiosis• Sex cells divide to produce gametes (sperm or egg).

• Gametes have half the # of chromosomes.

• Occurs only in gonads (testes or ovaries).

Male: spermatogenesisFemale: oogenesis

• Meiosis is similar to mitosis with some chromosomal differences.

Sex ChromosomesThe Sex Chromosomes code for the sex of the offspring.** If the offspring has two “X” chromosomes it will be a female. ** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male.

XX chromosome - female XY chromosome - male

In Humans the “Sex

Chromosomes” are the 23rd set

Boy or Girl? The Y Chromosome “Decides”

X chromosomeY chromosome

Interphase I

• Similar to mitosis interphase.

• Chromosomes replicate (S phase).

• Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres.

• Centriole pairs also replicate.

Interphase I•Nucleus and nucleolus visible.

nuclear membrane

nucleolus

cell membrane

chromatin

Prophase I• Longest and most complex phase (90%).

• Chromosomes condense.

• Synapsis occurs: homologous chromosomes come together to form a tetrad.

• Tetrad is two chromosomes or four chromatids (sister and nonsister chromatids).

Prophase I - Synapsis

Homologous chromosomes

sister chromatids sister chromatidsTetrad

Prophase I

centriolesspindle fiber

asterfibers

Crossing Over

•Crossing over (variation) may occur between nonsister chromatids

•Crossing over: segments of nonsister chromatids break and reattach to the other chromatid.

Crossing Over - variation

nonsister chromatids

chiasmata: site of crossing over

variation

Tetrad

Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over

Crossing-over multiplies the already huge number of different gamete types produced by independent

assortment.

Metaphase I• Shortest phase

• Tetrads align on the metaphase plate.

• INDEPENDENT ASSORTMENT OCCURS:1. The random separation of the homologous chromosomes---this results in GENETIC VARIATION

Homologous Chromosomes

• Pair of chromosomes (maternal and paternal) that are similar in shape and size.

• Homologous pairs (tetrads) carry genes controlling the same inherited traits.

• Each locus (position of a gene) is in the same position on homologues.

• Humans have 23 pairs of homologous chromosomes.

a. 22 pairs of autosomesb. 01 pair of sex chromosomes

Homologous Chromosomes

Paternal Maternal

eye color locus

eye color locus

hair color locus

hair color locus

Metaphase I

metaphase plate

OR

metaphase plate

Anaphase I• Homologous chromosomes separate and move towards the poles.

• Sister chromatids remain attached at their centromeres.

Anaphase I

Telophase I

• Each pole now has haploid set of chromosomes.

• Cytokinesis occurs and two haploid daughter cells are formed.

Telophase I

Meiosis II• No interphase II

(or very short - no more DNA replication)

• Remember: Meiosis II is similar to mitosis

Prophase II• same as prophase in mitosis

Metaphase II• same as metaphase in mitosis

metaphase platemetaphase plate

Anaphase II• same as anaphase in mitosis• sister chromatids separate

Telophase II

• Same as telophase in mitosis.

• Nuclei form.

• Cytokinesis occurs.

• Remember: four haploid daughter cells produced.

gametes = sperm or egg

Telophase II

Meiosis

2n=4

sex cell

diploid (2n)

n=2

n=2

meiosis I

n=2

n=2

n=2

n=2

sperm

haploid (n)

meiosis II

Meiosis – mouseParent cell

4 gametes

1st division

2nd division

Meiosis I

Draw This!

Meiosis II

Meiosis

Cells Dividing Clip

Crash Course Meiosis

Meiosis Pipe Cleaner Lab

Snowball Fight!