3.3: Meiosis
Teaching time: 2 hours Practical time allocated: 0
key vocabulary
Prior learning and retrieval practice
Review 1.6 cell division
Review 3.2 chromosomes
Essential idea: Alleles segregate during meiosis allowing new combinations to be formed by the fusion of gametes.
Exercise 1: Watch this video and connect-extend-challenge
Asexual and Sexual life cycles
U1: One diploid nucleus divides by meiosis to produce four haploid nuclei.
U2: The halving of the chromosome number allows a sexual life cycle with fusion of gametes.
Exercise 2: Compare and contrast asexual and sexual reproduction
Meiosis
U3: DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids.
U4: The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation.
U5: Orientation of pairs of homologous chromosomes prior to separation is random.
U6: Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number.
U7: Crossing over and random orientation promotes genetic variation. Guidance from the syllabus: The process of chiasmata formation need not be explained.
U8: Fusion of gametes from different parents promotes genetic variation.
Mechanisms of Meiosis Bio Review 04.04.2003.pdfExercise 3: Explain the stages of meiosis. Explain how variation in the offspring is produced through independent assortment, crossing over and random fertilisation.
Use the tutorial here to help you.
Drawing the stages of Meiosis
Nature of science: Making careful observations—meiosis was discovered by microscope examination of dividing germ-line cells. (1.8)
S1: Drawing diagrams to show the stages of meiosis resulting in the formation of four haploid cells. Guidance from the syllabus: Drawings of the stages of meiosis do not need to include chiasmata. 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.
Exercise 4: Draw diagrams to show the stages of meiosis
Non-disjunction and Down Syndrome
A1: Non-disjunction can cause Down syndrome and other chromosome abnormalities.
A2: Studies showing age of parents influences chances of non-disjunction.
Exercise 5: Explain what non-disjunction is and is relationship to Down Syndrome. What evidence is there to suggest that the age of parents influence the chance of non-disjunction.
Karyotype analysis
Prenatal diagnosis Bio Sci Rev.pdfA3: Description of methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling and amniocentesis and the associated risks.
Exercise 6: Outline the processes of chorionic villus sampling and amniocentesis. What are the risks associated with these processes.
