Meiosis

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Meiosis

• How sex cells are made!

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Asexual vs. Sexual Reproduction

• A. Asexual reproduction - quick and efficient.
• 1. Dont need a partner.
• 2. But your offspring are all
• clones no variation!
• Sex is not for everyone
• Because the environment is always changing, some
  offspring may not be as well adapted as the
  parents.
• Sex can be dangerous - spreading disease, risk of
  predation
• Sex requires energy to find a mate

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Why sex?

• B. Sexual reproduction- takes more energy!
• 1.You and your mate must find each other
• 2. Must exchange genetic material.
• 3. It is energetically expensive to construct
  and use mate-attracting body parts.
• Bottom Line Why is sexual reproduction so
  AWESOME for you?
• Because you and your mate BOTH pass
  characteristics to all your offspring, there will
  be natural VARIATION (differences) introduced by
  sex. These variations give your offspring
  selective advantages for survival in changing
  environments.

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Variation thanks to sexual reproduction- all
these puppies are slightly different genetically
even though they had the same parents
This will be important when we study EVOLUTION!
Hint hint!
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Intro to Genetics

• What will we study in the next few days?
• Meiosis- the process that makes sex cells which
  carry YOUR genetic info into your offspring
• Karyotypes- what your chromosomes look like
• Understanding how your genes get passed on
• Linking genetics to evolution (next chapter)

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Genetics- to generate

• Genetics is the branch of biology that deals with
  the study that explains how organisms inherit
  characteristics- inheritance may come from sexual
  or asexual reproduction.
• Asexual reproduction- mitotic division
• Sexual reproduction- meiotic divisions

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Two things are required in order for genetics to
work

• You must inherit a single copy of every gene from
  both your parents. Since you have two biological
  parents, you will have TWO complete sets of
  genes.
• 2. When YOU make your own gametes (sex cells),
  your two sets of genes must be separated from
  each other. Each of your gametes will have only
  one set of genes.

http//www.web-books.com/eLibrary/Medicine/Neonata
l/Images/CF_Inheritance.gif
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Chromosome Number

• Diploid (2N) 2 copies of each chromosome
• Haploid (1N) 1 copy of each chromosome
• Homologous chromosomes chromosomes that have
  same size, shape gene sequence

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Chromosome Number- Somatic cell (human)

• Diploid (2N) 46
• Haploid (1N) 23
• Homologous chromosomes 23 pairs of homologues
• Is this a karyotype of a somatic cell or gamete?

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Diploid vs. Haploid

1. Diploid- 2 sets of info 1 set of chromosomes
   from mom, other set from dad ONLY SOMATIC CELLS
2. Haploid- 1 set of genetic info 1 set of
   chromosomes ONLY GAMETES!

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http//www.web-books.com/eLibrary/Medicine/Neonata
l/Images/CF_Inheritance.gif
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How do organisms make gametes (1N) from germ
cells (2N)?

• Meiosis- a process that
• produces gametes
• is a reduction division- reduces the
  chromosome number in half (2N ? 1N)
• A diploid cell results in 4 UNIQUE and VARIED
  haploid cell
• 2 divisions

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Overview of Meiosis
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You and your siblings all have50 genetic info
from mom50 genetic info from dad

• Why dont all of you look the same?
• http//www.diffen.com/difference/Meiosis_vs_Mitosi
  s
• CROSSING OVER-
• genetic shuffling of info
• nonsister chromatids cross parts of themselves
  during Prophase I of the first meiotic division
  (Meiosis I)
• genetic recombination occurs- you end up with
  gametes that are all a little different but still
  50 mom and 50 dad info

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Lab- Meiosis Phases Activity

• Grab your lab books. Title activity as above.
• Name, date, period.
• You will work individually.
• Cut out each phase of meiosis.
• Paste/tape the phases in order (book pg. 276-7)
• Name each phase
• Describe what is occurring at each phase.
• Label Meiosis I and Meiosis II
• Answer the following questions
• What is the importance of meiosis.
• List 3 ways meiosis is DIFFERENT from mitosis.
• List 2 ways meiosis is SIMILAR to mitosis.

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Links to check out useful info and animations

• http//www-bcf.usc.edu/forsburg/meiosis.html
• http//www.youtube.com/watch?vZ0ujlwWQXzM
• http//meiosistheprocess.wikispaces.com/MeiosisVi
  deo (this site has lots of great options for
  learning meiosis!)
• http//www.hhmi.org/bulletin/nov2008/features/ (a
  very good reading that gets into the details)
• http//mercury.bio.uaf.edu/kevin_mccracken/geneti
  cs/labs/lab1/lab-1b.pdf (helpful notes on all
  the phases)

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Interphase I

• DNA Replication occurs (exact copy of DNA made)

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Prophase I

• Chromosomes pair with their homologous
  chromosomes
• Crossing-over exchange of alleles between
  homologous chromosomes

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Metaphase I

• Homologous chromosomes line up on equator
• Spindle fibers attach to centromeres

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Anaphase I

• Homologous chromosomes separate

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Telophase I Cytokinesis

• Nuclear membrane reforms
• Cell separates into 2 cells
• Daughter cells are haploid
• Chromosome sets and alleles unique in each cell

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Prophase II

• 2 haploid cells
• No chromosome replication
• Each chromosome has 2 chromatids

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Metaphase II

• Chromosomes line up on equator
• Spindle fibers attach at the centromere

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Anaphase II

• Sister chromatids separate
• Chromatids pulled to opposite poles

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Telophase II Cytokinesis

• New nuclear envelopes reform
• 4 daughter cells
• All are haploid, 1N (one set of chromosomes)
• Non-identical (different alleles)

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Gamete formation

• In males, meiosis produces 4 sperm
• In females, meiosis produces 1 egg and 3 polar
  bodies

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Comparing Mitosis Meiosis
Mitosis Meiosis
Creates 2 diploid cells Creates 4 haploid cells
2 daughter cells with identical sets of chromosomes and alleles 4 daughter cells with different alleles on each chromosome
Allows organism to grow and replace cells Allows organisms to produce gametes for sexual reproduction
How organisms reproduce asexually Allows organisms to produce gametes for sexual reproduction
Animation
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http//kvhs.nbed.nb.ca/gallant/biology/mitosis_mei
osis.html