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Cell Division (1.6/3.3/10.1)

HHMI Cell Division WebQuest


Cell Division WebQuest




YouTube Video


YouTube Video


YouTube Video





Cancer Video Clips:

YouTube Video


YouTube Video


1.6 Cell division

Nature of science:

Serendipity and scientific discoveries—the discovery of cyclins was accidental. (1.4)

Understandings:

Mitosis is division of the nucleus into two genetically identical daughter nuclei.

Chromosomes condense by supercoiling during mitosis.

Cytokinesis occurs after mitosis and is different in plant and animal cells.

Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm.

Cyclins are involved in the control of the cell cycle.

Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.

Applications and skills:

Application: The correlation between smoking and incidence of cancers.

Skill: Identification of phases of mitosis in cells viewed with a microscope or in a micrograph.

Skill: Determination of a mitotic index from a micrograph.

Guidance:

The sequence of events in the four phases of mitosis should be known.

Preparation of temporary mounts of root squashes is recommended but phases in mitosis can also be viewed using permanent slides.

To avoid confusion in terminology, teachers are encouraged to refer to the two parts of a chromosome as sister chromatids, while they are attached to each other by a centromere in the early stages of mitosis. From anaphase onwards, when sister chromatids have separated to form individual structures, they should be referred to as chromosomes.

International-mindedness:

Biologists in laboratories throughout the world are researching into the causes and treatment of cancer.

Theory of knowledge:

A number of scientific discoveries are claimed to be incidental or serendipitous. To what extent might some of these scientific discoveries be the result of intuition rather than luck?

Utilization:

The mitotic index is an important prognostic tool for predicting the response of cancer cells to chemotherapy.

Aims:

Aim 8: The tobacco industry could be discussed. Suppression of the results of research by tobacco companies into the health effects of smoking tobacco was unethical. Smoking causes considerable social harm, but, with the exception of laws on production and supply in Bhutan, has never been made illegal.

3.3 Meiosis

Nature of science:

Making careful observations—meiosis was discovered by microscope examination of dividing germ-line cells. (1.8)

Understandings:

One diploid nucleus divides by meiosis to produce four haploid nuclei.

The halving of the chromosome number allows a sexual life cycle with fusion of gametes.

DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids.

The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation.

Orientation of pairs of homologous chromosomes prior to separation is random.

Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number.

Crossing over and random orientation promotes genetic variation.

Fusion of gametes from different parents promotes genetic variation.

Applications and skills:

Application: Non-disjunction can cause Down syndrome and other chromosome abnormalities.

Application: Studies showing age of parents influences chances of non-disjunction.

Application: Description of methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling and amniocentesis and the associated risks.

Skill: Drawing diagrams to show the stages of meiosis resulting in the formation of four haploid cells.

Guidance:

Preparation of microscope slides showing meiosis is challenging and permanent slides should be available in case no cells in meiosis are visible in temporary mounts.

Drawings of the stages of meiosis do not need to include chiasmata.

The process of chiasmata formation need not be explained.

Theory of knowledge:

In 1922 the number of chromosomes counted in a human cell was 48. This remained the established number for 30 years, even though a review of photographic evidence from the time clearly showed that there were 46. For what reasons do existing beliefs carry a certain inertia?

Utilization:

An understanding of karyotypes has allowed diagnoses to be made for the purposes of genetic counselling.

Aims:

Aim 8: Pre-natal screening for chromosome abnormalities gives an indication of the sex of the fetus and raises ethical issues over selective abortion of female fetuses in some countries.

Essential idea: The inheritance of genes follows patterns.

10.1 Meiosis

Nature of science:

Making careful observations—careful observation and record keeping turned up anomalous data that Mendel’s law of independent assortment could not account for. Thomas Hunt Morgan developed the notion of linked genes to account for the anomalies. (1.8)

Understandings:

Chromosomes replicate in interphase before meiosis.

Crossing over is the exchange of DNA material between non-sister homologous chromatids.

Crossing over produces new combinations of alleles on the chromosomes of the haploid cells.

Chiasmata formation between non-sister chromatids can result in an exchange of alleles.

Homologous chromosomes separate in meiosis I.

Sister chromatids separate in meiosis II.

Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I.

Applications and skills:

Skill: Drawing diagrams to show chiasmata formed by crossing over.

Guidance:

Diagrams of chiasmata should show sister chromatids still closely aligned, except at the point where crossing over occurred and a chiasma was formed.

Aims:

Aim 6: Staining of lily anthers or other tissue containing germ-line cells and microscope examination to observe cells in meiosis are possible activities.

Essential idea: Genes may be linked or unlinked and are inherited accordingly.




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Jessica Clark,
Feb 12, 2014, 10:15 AM
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Jessica Clark,
Feb 12, 2014, 10:15 AM
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Jessica Clark,
Feb 10, 2015, 3:52 AM
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Jessica Clark,
Feb 10, 2015, 3:52 AM
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Jessica Clark,
Feb 12, 2014, 10:15 AM
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Jessica Clark,
Feb 10, 2015, 3:52 AM
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Jessica Clark,
Feb 12, 2014, 10:16 AM
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