Starter In terms of chromosome number what must happen to human reproductive cells so reproduction can take place? Why?

Meiosis

What is it? A type of cell division that creates gametes for sexual reproduction – Gametes: Egg (female)Sperm (male)

Haploid vs. Diploid Gametes are haploid (1N) – Contains one set of chromosomes Gametes come together to form a diploid (2N) cell during fertilization. – Zygote – Contains two complete sets of chromosomes One was from the father, one was from the mother

Humans Each one of our cells has 46 chromosomes – A set of 23 from Mom, a set of 23 from Dad Our haploid number is… – 23 Our diploid number is… – 46

Homologous Pairs In a diploid cell, the matching pairs of chromosomes are called Homologous Pairs – For every chromosome from an egg, there is a matching one from the sperm Autosomes Which pair does not fit this rule?

The 23 rd pair (in humans) – The sex pair! Answers the question…female or male? XX (female) XY (male)

Sexual Reproduction The process by which the chromosomes of two parents combine to produce offspring – Fertilization – egg cell and sperm cell join to produce a new individual – Zygote – a fertilized egg The SINGLE CELL produced by fertilization

Why is Meiosis important? Two Reasons 1. The production of reproductive cells containing only one set of chromosomes is vital. Why? - For making sure that species has the same number of chromosomes from generation to generation

2. Genetic variation made possible - Meiosis increases the amount of different characteristics you see among individuals that make up the population of a species. - 4 Causes of Genetic Variation

Crossing Over 1.The exchange of genes (pieces of DNA) between pairs of homologous chromosomes – When done, each chromosome in the homologous pair has a different combination of genes compared to before Meiosis began

Random Fertilization 2.Many of sperm to one egg – During reproduction a man emits approximately 120 million sperm. Each of these sperm contains unique set of chromosomes 3.Random Mating

Independent Assortment 4.The homologous pairs line up independently of one another during Metaphase I.

What does this explain? I may look similar to my family members but none of us is exactly the same.

Except for… Identical twins!

What is meiosis? Why is meiosis so important? What is a gamete? Define Diploid. What is our human diploid number? – Fruit flies have 8 chromosomes 2N = ? – Goldfish have 94 chromosomes 2N = ? Define Haploid – Humans 1N = ? – Fruit Flies 1N =? – Goldfish 1N =? Define a Homologous Pair. What is a zygote? Diploid or Haploid? Explain Crossing over.

The Phases Meiosis I – Prophase I – Metaphase I – Anaphase I – Telophase I/Cytokinesis Meiosis II – Prophase II – Metaphase II – Anaphase II – Telophase II/Cytokinesis

Meiosis I Prophase I – Chromatin condenses – Chromosomes of homologous pairs match up and become tangled together. (4 chromatids in each chromosome pair). Crossing over occurs – Nucleolus and nuclear membrane disappear – Centrioles move to opposite sides of the nucleus – Spindle fibers attach to centromeres

Draw Prophase I

Meiosis I Metaphase I – Centrioles move to opposite sides of the cell – The tangled pairs of chromosomes separate and the homologous pairs line up next to each other in the middle of the cell

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Meiosis I Anaphase I – Homologous pairs of chromosomes separate from each other – Spindle fibers shorten pulling one member from each pair to opposite sides of the cell

Draw Anaphase I

Meiosis I Telophase I/Cytokinesis – Chromosomes uncoil back to chromatin – Nuclear membrane may or may not form around both bundles of chromatin at opposite ends of the cell – Spindle fibers disappear – Cytoplasm divides creating two, identical daughter cells that contain one half the number of chromosome pairs as the parent cell

Draw Telophase I/Cytokinesis

Each of the two daughter cells goes back for round 2!

Meiosis II Prophase II – Chromatin condenses – Nuclear membrane disappears – Centrioles move to opposite sides of the nucleus – Spindle fibers attach to centromeres

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Meiosis II Metaphase II – Centrioles move to opposite sides of the cell – Chromosomes line up in the middle of the cell

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Meiosis II Anaphase II – Centromeres that join the sister chromatids split – Sister chromatids becoming separate chromosomes – Spindle fibers shorten

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Meiosis II Telophase II/Cytokinesis – Chromosomes uncoil becoming chromatin – Nuclear membrane forms around both bundles of chromatin at opposite ends of the cell – Nucleolus reappears in each new daughter cell – Spindle fibers disappear – Cytoplasm divides creating 2 haploid gametes from each daughter cell created in Meiosis I. Each gamete has half the number of chromosomes as its parent cell.

Draw Telophase II/Cytokinesis

Now you tell me… What makes each process important? Compare and contrast Mitosis and Meiosis using the Venn Diagram.

Let’s Compare Mitosis – Results in 2 daughter cells when complete – Chromosomes identical to parent cell – Offspring identical to parent – Same number of chromosomes in daughter cells as in the parent cells Meiosis – Results in 4 daughter cells when complete – Chromosomes may be different from parent cell – Offspring different from parent – Half of the number of chromosomes in the daughter cells as in the parent cells