3.3 Meiosis

Essential Idea:

Understandings:

One diploid nucleus divides by meiosis to produce four haploid nuclei
Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number
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
The halving of the chromosome number allows a sexual life cycle with fusion of gametes
Crossing over and random orientation promotes genetic variation
Fusion of gametes from different parents promotes genetic variation

Applications:

Non-disjunction can cause Down syndrome and other chromosomal abnormalities
Studies showing age of parents influences chances of non-disjunction
Description of methods used to obtain cells for karyotype analysis – e.g. chorionic villus sampling and amniocentesis and the associated risks

Skills:

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

Nature of science:

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

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?
Additionally to what extend is cognitive inertia governed by the brain's neurobiology?

3.3 Meiosis.pptx

3.3 Meiosis.pdf

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