Class objectives
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Class Objectives:.  Distinguish between haploid and diploid cells and its relation to meiosis and fertilization. D istinguish the various phases of meiosis due to the position of the chromosomes at that particular phase.

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Class Objectives:

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Class objectives

Class Objectives:

Distinguish between haploid and diploid cells and its relation to meiosis and fertilization.

Distinguish the various phases of meiosis due to the position of the chromosomes at that particular phase.

 Explain the reason meiosis reduces the number of chromosomes by one half so that when gametes are fertilized the number of chromosomes is restored.

 Compare and contrast the cells produced by both mitosis and meiosis and the fate of the cells from each cycle.


Haploid vs diploid

Haploid vs. Diploid

  • Diploid (2n)

    • A cell with two of each kind of chromosome

    • ex) somatic cells

  • Haploid (n)

    • A cell with one kind of chromosome

    • ex) germ cells

  • In mitosis, cells are dividing to form diploid cells

  • In meiosis, cells are dividing to form haploid cells


The phases of meiosis

The Phases of Meiosis

Meiosis I & Meiosis II


Meiosis i

Meiosis I

  • Consists of:

    • Prophase I

    • Metaphase I

    • Anaphase I

    • Telophase I

    • Cytokinesis I

  • Before meiosis begins, what must happen to the cell’s DNA/chromosomes?


Prophase i

Prophase I

Like prophase of mitosis:

  • The nucleus and nuclear envelope disappears.

  • Centrioles move to the opposite poles and the spindle fibers form between the centrioles.

  • Chromosomes condenses into sister chromatids.

    Unlike prophase of mitosis:

  • Pairs of homologous chromosomes form a tetrad.

  • Crossing over may occur.

    • Exchange of genetic material


Metaphase i

Metaphase I

  • Spindle fibers attach to centromeres.

  • Tetrads line up at the spindle’s equator.

    Unlike mitosis:

  • Homologous chromosomes are lined up side by side as tetrads.


Anaphase i

Anaphase I

  • Tetrads, which consist of two homologous chromosomes separate.


Telophase i cytokinesis i

Telophase I/Cytokinesis I

  • The nucleus and nuclear envelope reappears. disappears.

  • The spindle is broken down and the chromosomes uncoil.

  • Cytokinesis, the division of the cytoplasm and the organelles begins and ends forming two cells.


Mitosis ii

Mitosis II

  • Consists of:

    • Prophase II

    • Metaphase II

    • Anaphase II

    • Telophase II

  • The purpose of meiosis II is to separate sister chromatids of each chromosome into separate cells.


Prophase ii

Prophase II

  • The nucleus and nuclear envelope disappear.

  • Spindle fibers and centrioles form.

  • Chromosomes condenses into sister chromatids.


Metaphase ii

Metaphase II

  • Sister chromatids attach to the centromere.

  • Sister chromatids line up at the equator.


Anaphase ii

Anaphase II

  • Sister chromatids separate into two chromosomes.

  • Chromosomes move to the opposite poles.


Telophase ii cytokinesis ii

Telophase II/Cytokinesis II

  • The nucleus and nuclear envelope reforms.

  • The spindles breakdown.

  • The cytoplasm divides

  • 4 haploid cells are formed.


Fertilization

Fertilization

  • The 4 haploid cells formed in meiosis will become gametes.

  • Gametes are:

    • Sperm in males (haploid)

    • Eggs in females (haploid)

  • Gametes transmit the genes they contain to their offspring.

  • When a sperm fertilizes an egg a zygote is formed  this is called sexual reproduction

  • A zygote is a diploid cell.

    • Sperm (haploid) + Egg (haploid) = zygote (diploid)


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