Genetics Meiosis page 24 study guide

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Genetics Meiosis page 24 study guide

• Key words
• Haploid
• Diploid
• Homologous
• Reduction division

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• Sexual reproduction new individual by a
  combination of two haploid sex cells (gametes).
• Fertilization combination of genetic
  information from two separate cells that have one
  half the original genetic information

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Page 24 sg

• Female- produces an egg
• Male produces sperm
• Both gametes are haploid (n) or a single set of
  chromosomes
• new individual called a zygote, with two sets of
  chromosomes (diploid or 2n).
• Meiosis is a process to convert a diploid cell to
  a haploid gamete, and cause a change in the
  genetic information to increase diversity in the
  offspring.

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Ploidy Number of sets of chromosomes in a cell

• Haploid (n)-- one set chromosomes
• Diploid (2n)-- two set of chromosomes. Most plant
  and animal adults are diploid (2n)
• Eggs and sperm are haploid (n)

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Chromosomes in a Diploid Cell

• Summary of chromosome characteristics
• Diploid set for humans 2n 46
• Autosomes homologous chromosomes, one from each
  parent (humans 22 sets of 2)
• Sex chromosomes (humans have 1 set of 2)
• Female-sex chromosomes are homologous (XX)
• Male-sex chromosomes are non-homologous (XY)

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Reduction Division

• Living organisms which reproduce sexually halve
  their chromosome number in preparation for fusion
  of gametes.

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Lets watch

• Meiosis

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Meiosis divided into meiosis I and meiosis II
(me1 and me2)

• Page 24 sg
• Page Prophase I pairing of homologous
  chromosomes
• Called synapsis
• Animations (unique features )

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Prophase 1

• Homologs find their partner becoming intimately
  associated forming a synaptonenal complex ,a
  lattice of proteins
• This is called a tetrad

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• Over view of process. http//barleyworld.org/educ
  ational/meiosisline39.swf

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Prophase 1 page 24 study guide

• With this relationship of homologs crossing over
  occurs. This is an exchange of genetic
  information which leads to continued diversity.
• The site of crossing over is called chiasmata.

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Prophase 1

• Chromosomes pair up as homologous chromosomes
• Nuclear membrane disappears
• Spindle mt grow from each pole

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Prophase 1
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Crossing Over

• Crossing Over Causes Genetic Variation

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Metaphase I

• Terminal chiasmata hold homologs together.
• Only one side of centromere facing outward.
• Spindle attaches to only one side, which will
  pull sister together.

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Anaphase I

• Microtubules shorten
• Break chiasmata
• At finish each pole has a full set of chromosomes
  which have been independently assorted.

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Telophase I

• Chromosomes cluster
• Nuclear membrane forms

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Meiosis II

• Division time variable but typically a short
  Interphase
• Cytokinesis may or may not occur
• No synthesis

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Prophase II

• Breakdown nuclear membrane
• Centrioles form and move toward the poles
• New spindles form

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Metaphase II

• Microtubules grow from the centrioles and attach
  to the centromeres
• The sister chromatids line up along the cell
  equator

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Anaphase II

• The centromeres break and sister chromatids
  separate 
• Cytokinesis begins

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Telophase II

• The chromosomes may decondense (depends on
  species)
• Cytokinesis reaches completion, creating four
  haploid daughter cells

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• Remainder of animations including a look at the
  comparison of mitosis and meiosis
• Animations

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Review

• Meiosis
• meiosis double cell division