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Lecture 5

BIO152H5 Lecture Notes - Lecture 5: Homologous Chromosome, Sister Chromatids, Nuclear Membrane

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Maria Arts

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BIO152 Lecture 5: Meiosis- Why Sexual Reproduction
-Understanding Meiosis: how and why?
-Phases of Meiosis
-Meiosis and genetic variations
-Errors in meiosis
-Comparing asexual and sexual reproduction
-Advantages of Meiosis
Chromosomes and Meiosis
-There are 23 types of chromosomes and 2 chromosomes of each type (homologous
chromosomes, one from each parent).
-X and Y are sex chromosomes:
o‘XX’ represent female.
o‘XY’ represent male.
-For humans, 2n=46.
Meiosis-Sexual Reproduction
-Two haploid gametes (having a single set of unpaired chromosomes)- one from each
parent, unite in fertilization to form a genetically unique, diploid (containing two
complete set of chromosomes, one from each parent) zygote (a cell formed by the union
of two gametes: the developing individual produced from such a cell).
-Sexual reproduction involves the alternation of meiosis and fertilization.
-Meiosis is a mechanism for diversity: the parent nucleus produces four haploid daughter
nuclei, each different from the parent and from its sister.
Major Events in Meiosis
-A) Each chromosome replicates prior to undergoing meiosis, similar as mitosis, where
chromosomes replicate before undergoing cell division.
-B) During meiosis, chromosomes number in each cell is reduced.
-Homologous chromosomes will pair.
-Will have 4 daughter cells as a result.
-They will be genetically different.
-C) A full complement of chromosomes in restored during fertilization.
-After fertilization, you have diploid gametes.
-Via meiosis, you produce gametes, which will produce diploid gametes.
Phases of Meiosis 1
-Meiosis is a continuous process.
-Meiosis 1 is the first division of Meiosis.
-Meiosis 1 begins with a diploid parent cell and produces two daughter cells that will then
progress through meiosis 2.
-Interphase- Replication of nuclear membrane
-Prophase- Condensation of DNA in chromosomes, synapsis occurs (the side by side
pairing of homologous material and paternal chromosomes at the start of meiosis).
-Prometaphase- Dissolution of nuclear membrane
-Metaphase- Movement of chromosomes to midline
-Anaphase- Separation of homologous chromosome
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