Meiosis

Topic 3.3: Meiosis

Essential Idea: Alleles segregate during meiosis allowing new combinations to be formed by the fusion of gametes.

At SHS, Topic 3.3 is taught in the following class unit(s):

Chromosomes (unit 15)
Meiosis (unit 16)

Statements & Objectives:

3.3.U1 One of diploid nucleus divides by meiosis to produce four haploid nuclei.

Compare divisions of meiosis I and meiosis II.

3.3.U2 The halving of the chromosomes number allows a sexual life cycle with fusion of gametes.

Compare sexual and asexual life cycles.
Explain why meiosis must occur as part of a sexual life cycle.

3.3.U3 DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids.

State that DNA is replicated in interphase before meiosis.
Given a diploid number (for example 2n=4), outline the movement and structure of DNA through the stages of meiosis.

3.3.U4 The early stages of meiosis involves pairing of homologous chromosomes and crossing over followed by condensation.

List three events that occur in prophase 1 of meiosis.
Define bivalent and synapsis.
Outline the process and result of crossing over.

3.3.U5 Orientation of pairs of homologous chromosomes prior to separation is random.

Describe the attachment of spindle microtubules to chromosomes during meiosis I.
Describe random orientation of chromosomes during meiosis I.

3.3.U6 Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number.

Explain why meiosis I is a reductive division.
State that cells are haploid at the end of meiosis I.

3.3.U7 Crossing over and random orientation promotes genetic variation.

Explain how meiosis leads to genetic variation in gametes.
State the the number of chromosome combinations possible due to random orientation is 2^n.

3.3.U8 Fusion of gametes from different parents promotes genetic variation.

Outline the role of fertilization as a source of genetic variation.

3.3.A1 Non-disjunction can cause Down syndrome and other chromosome abnormalities. Studies showing age of parents influences chances of non-disjunction.

Define non-disjunction.
State the result of nondisjunction.
Describe the cause and symptoms of Down syndrome.
Explain the relationship between parental age and chances of non-disjunction.

3.3.A2 Description of methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling and amniocentesis and the associated risks.

Describe the two procedures for obtaining fetal cells for production of a karyotype.

3.3.S1 Drawing diagrams to show the stages of meiosis resulting in the formation of four haploid cells.

Outline the events of prophase, metaphase, anaphase and telophase in meiosis I and meiosis II.
Draw diagrams of cells in prophase, metaphase, anaphase and telophase in meiosis I and meiosis II.

3.3.NOS Making careful observations- meiosis was discovered by microscope examination of dividing germ-line cells.

Discuss difficulties in microscopic examination of dividing cells.
Describe the discovery of meiosis.

In the News:

How chromosomes 'cheat' for the chance to get into an egg (2017-11-02)
Scientists identify Down's Syndrome gene (2016-08-09)
From the somatic cell to the germ cell (2017-06-08)
Cells simply avoid chromosome confusion (2014-09-15)