Meiosis Concept Presentation

Riffat Asif and Ezgi Cetinkaya

D 2.2. and D 3.1

Meiosis Square Dance

• http://www.youtube.com/watch?v=iCL6d0OwKt8

Curriculum Expectations

• D 2.2 : investigate the process of meiosis, using a microscope or similar instrument, or a computer simulation, and draw biological diagrams to help explain the main phases in the process

• D 3.1 : explain the phases in the process of meiosis in terms of cell division, the movement of chromosomes, and crossing over of genetic material

Lesson Sequence

Meiosis IProphase IMetaphase IAnaphase ITelophase IInterkinesis

Meiosis IIProphase IIMetaphase IIAnaphase IITelophase IICytokinesis

Who Cares?

No Meiosis, No Fertilization.

No Fertilization, No Offspring.

No Offspring, No Family, No Future

Student Misconceptions/Difficulties• Students may have trouble differentiating

between the stages of meiosis and mitosis. Have them compare these two processes in a chart or via a graphic organizer

Meiosis

And Mitosis

What D o We Know about Mitosis?

Makes Two Identical Daughter CellsSister Cell Are DiploidGrowth and Repair Of Tissue

MITOSIS

Essential For Growth And Repair of Animals, Plants Human Tissue.

Mitosis will help me grow

Sooner Mitosis Happens the

sooner I can get this thing out of my

head

Mitosis will heal my Wounds

Meiosis vs. Mitosis (A comparison) MITOSIS MEIOSIS

Occurs in somatic cells Occurs in germ cells as part of the sexual cycle

Haploid and diploid cells can undergo mitosis- one round of division

Only diploid cells undergo meiosis- 2 rounds of division, meiosis I and II

Preceded by S phase- chromosome duplication

Chromosomes duplicate before meiosis I but not before meiosis II

Homologous chromosomes do not pair

Homologous chromosomes pair along their length during prophase of meiosis I

Genetic exchange between homologous chromosomes very rare

Crossing-over occurs between homologous chromosomes during prophase of meiosis I

Mitosis vs. Meiosis continuedMITOSIS MEIOSIS

Sister chromatids attach to spindle fibers from opposite poles during metaphase

Sister chromatids do not attach, rather homologous chromosomes attach to spindle fibers from opposite poles during metaphase I

Centromere splits at the beginning of anaphase

Centromere does NOT split during meiosis I

- Sister chromatids attach to spindle fibers from opposite poles during metaphase II

- Centromere splits at the beginning of anaphase II

Produces 2 new daughter cells, identical to each other and the original cell

Produces 4 haploid cells, one (egg) or all (sperm) of which can become gametes- none is identical to each other or to original cell

Meiosis I

Meiosis IProphase IMetaphase IAnaphase ITelophase IInterkinesis

Prophase I

• Chromosomes thicken becoming visible• Centrosomes begin to movetoward opposite poles• Crossing over, genetic exchange between non-sister chromatids • Spindle begins to form

Metaphase I

• Tetrads line up along metaphase plate• Each chromosome of a homologous pair attaches fibers from opposite poles• Sister chromatids attach to fibers from the same pole

Anaphase I

• Centromere does not divide • Chiasmata migrate off chromatid ends• Homologous chromosomes move to opposite poles

Telophase I

• Nuclear envelope re-forms• Result: cells have half the # ofchromosomes, each consisting of two sister chromatids

Interkinesis

• No chromosomal duplication (as opposed to mitosis)

• In some species chromosomes decondense

Meiosis II

Meiosis IIProphase IIMetaphase IIAnaphase IITelophase IICytokinesis

Prophase II

• Chromosomes condense• Centrioles move towards opposite poles• *Nuclear envelope breaks down at the end of prophase II

Metaphase II

• Chromosomes align at the metaphase plate • Sister chromatids attach to spindle fibers from opposite poles

Anaphase II

• Centromeres divide

• Sister chromatidsmove to opposite poles

Telophase II

• Chromosomes begin to uncoil

• Nuclear envelopes and Nucleoli reform

Cytokinesis

• Cytoplasm dividesforming 4 new haploidcells

Great Educational Video Clips

• http://www.cellsalive.com/meiosis.htm• Allows students to become active in their learning

• http://www.youtube.com/watch?v=R_LUJSqeSrI• An excellent video that is great to apply especially for those kinesthetic learners

Meiosis Virtual Lab

• A great virtual lab that students can investigate online

http://bio.rutgers.edu/~gb101/lab10_meiosis/meiosis_web/index10.html

Virtual Lab

• Students are able to become active in their learning, they are able to identify each of the stages through various microscopic images. Information is provided for them throughout the activity

• There is also a section in the lab where students are able to construct karyotypes- can be provided for those students who need to be further challenged

Click the image above to choose the stage of meiosis I the cells are in

Click on one of the cells above to get meiosis stage II choices

Some Virtual Lab Activities

Safety Considerations for Lab

• Students should be monitored during the virtual lab activity to make sure that they are not using the wrong website and to make sure that they are staying on track to the activity

• Internet safety- usually schools sets up firewalls to avoid unsafe websites but make sure to educate both yourself and students of the risks involved with internet safety

Significance of Meiosis:

Genetic Variation caused by the possible combinations of chromosomes during “Crossing Over” in Meiosis 1. Crossing over increase genetic diversity as the genes on the chromosomes combine in number of ways.

An alteration in the DNA structure during meiosis cause mutations.

In most cases mutations are maladaptive and the new cell dies.

A small number of mutations are viable ----- the cell survives. If the mutant gamete combines with another gamete to produce an offspring ---- the mutation can be passed to the next generation.

Exploring Further: Practical and Societal Applications

GENETIC DISORDERS AND MUTATIONS:

Sometimes the chromosomes after crossing over separates and move to one pole instead of opposite poles.

When the chromosomes do not separate it is called as: “ non disjunction”. The gametes with extra chromosome fertilize, the zygote has three chromosomes instead of the normal 2. This is called “Trisomy of chromosome 21”

Exploring Further: Practical and Societal Applications

Traits and Phenotype of animals

Traits are distinguished characteristics that are inherited.

Traits are inherited in discrete units called genes located on the chromosomes.

Exploring Further: Practical and Societal Applications

Trisomy 21 ----- Down Syndrome

The most common chromosomal disorder with incidence of 1:700 live births in U.S.

High correlation between maternal age and meiotic non- disjunction” leading to Trisomy 21.

Other abnormalities related to Trisomy 21 are: Congenial heart disease Dimorphic features Mental retardation Predisposition to Leukemia Abnormal Immune response Auto immunity

Exploring Further: Practical and Societal Applications

Differentiated Assessment

• Guided practice and formative assessment, summative assessment

• Brain-storming activities, presentation of videos for refreshing students’ prior knowledge

• Graphic organizers• Different activities and presentation styles to

gear to the many learning styles, ELL and IEL learners (e.g. youtube video presents an excellent activity for the kinesthetic learners)

More Resources and References

• http://www.carolguze.com/text/442-3-cell_cycle_mitosis_meiosis.shtml

• http://www.biology.iupui.edu/biocourses/N100/2k4ch9meiosisnotes.html

• http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect16.htm

• Hartwell, L., Hood, L., Goldberg, M., Reynolds, A., Silver, L., & Veres, R. (2008). Genetics: From genes to genomes. (3rd ed., pp. 96-97). New York: McGraw-Hill