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Meiosis
Meiosis
6.3
Meiosis
A process of nuclear division that reduces the number of chromosomes into half.
Produces haploid gametes.
Provides genetic variation from one generation to another through the process of crossing-over, independent assortment and random fertilisation.
Occurs in the gonads; testes and ova (humans); anther and ovary (flowering plants).
Consists of two separate nuclear divisions; meiosis I and meiosis II.
The cell undergoes interphase before entering meiosis.
Meiosis I:
Phase
Key event
Prophase I
Chromosomes condensed and thickened.
Homologous chromosomes paired up to form bivalents through synapsis.
Non-sister chromatids of homologous chromosomes exchange the DNA segments through crossing-over.
It leads to genetic recombination.
Centrioles migrate to opposite poles and form spindle fibres.
Nucleolus and nuclear membrane disappear.
Metaphase I
Spindle fibres pull the homologous chromosomes to the middle cell and aligned at the metaphase plate side by side.
The homologous chromosomes are arranged independently.
Anaphase I
Spindle fibres pull the homologous chromosomes to the opposite poles.
Each chromosome still consists of two sister chromatids.
Telophase I and cytokinesis
The chromosomes arrived at both poles.
Each pole now has a haploid daughter nucleus because it contains one set of chromosome.
Spindle fibres disappear, nucleolus and nuclear membrane reappear.
Produce two haploid daughter cells.
Each daughter cell receives one chromosome from the homologous pair.
Meiosis II:
The process is similar to mitosis.
Produce four haploid cells which are genetically different from one another and parent cell.
Effects of Uncontrolled Meiosis:
Abnormal meiosis leads to non-disjunction of chromosomes.
Non-disjunction chromosomes lead to Turner's syndrome, Klinefelter's syndrome, XYY males and XXX females.
Chapter : Cell Division
Topic : Meiosis
Form 4
Biology
View all notes for Biology Form 4
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