Meiosis and Sexual Reproduction Notes

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Meiosis and Sexual Reproduction Notes

• To be used with Meiosis and Sexual Reproduction
  Guided Notes

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From poppa
From momma
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Gametogenesis

• Gametogenesis the formation of gametes (eggs and
  sperm)
• Each species has a characteristic number of
  chromosomes
• Homologous Chromosomes the two members of a pair
  of chromosomes
• contain genes for the same traits

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Diploid vs. Haploid

• Diploid Number the number of chromosomes found
  in all body cells (2n)
• Haploid Number 1/2 the diploid number of
  chromosomes (n)
• found in the egg and sperm cells of a species

DIPLOID
HAPLOID
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Gametogenesis Terms

• Gametes eggs or sperm
• Gonads specialized organs in higher animals
  where the gametes are made
• Ovaries female gonads
• Testes male gonads

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Meiosis

• Meiosis process which involves a 1/2 reduction
  division of the chromosome number
• Haploid nuclei are formed which contain only one
  chromosome of the original pair
• Meiosis ONLY occurs in the gamete producing cells
  of the gonads (testes and ovaries)
• The production of sex cells

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First Meiotic Division- Interpahse1

1. DNA and chromosomes replicate

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Prophase 1

• Each chromosomes pairs with its matching
  homologous chromosome forming a tetrad
• Crossing-over occurs here

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Metaphase 1

• Spindle fibers attach to the homologous
  chromosomes

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Anaphase 1

• Spindle fibers pull homologous chromosomes to
  opposite ends of the cell

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Telophase 1

• Nuclear membrane forms.
• Cytokinesis occurs forming 2 new daughter cells
  having half the of chromosomes.

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Meiosis Terms

• Synapsis the meeting of two homologous
  chromosome pairs
• Tetrads the two pairs of homologous chromosomes
• Crossing Over the exchange of chromosome pieces
  in the tetrad during crossing over
• Crossing over increases the variability of the
  offspring
• This is why the offspring of sexual reproduction
  show many variations

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Crossing Over
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Meiosis 2- Very similar to Mitosis
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Prophase 2

• Nuclear membrane disappears and spindle fibers
  form

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Metaphase 2

• Chromosomes line up in the middle

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Anaphase 2

• Chromosomes are divided in half (centromere is
  split)

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Telophase 2

• Cells divide in half again (cytokinesis)
• Produced 4 haploid (n) daughter cells

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Meiosis, continued

• Disjunction Homologous pairs of chromosomes
  separate and move toward opposite poles of the
  cell
• Nondisjunction the failure of homologous
  chromosomes to separate

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Nondisjunction
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Nondisjunction

• Down's syndrome results from the nondisjunction
  of chromosome 21
• individual has an extra 21st chromosome
• polyploidy having an entire extra set of
  chromosomes
• Will result in the 3n or 4n number of chromosomes

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Downs Syndrome Rates
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Cyclopia

• Nondisjunciton of chromosome 13-15 or 17-18
• Two eyes within one orbit
• Proboscis-like appendage above the eye
• Low-set or missing ears
• Missing facial bones
• Congenital heart disease
• (do not survive)

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Turners syndrome

• XO sex chromosomes
• 1/2000 female births
• Short stature
• Wide-spaced underdeveloped nipples
• Webbed neck
• Swelling of hands feet
• Sterile

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Klinefelters Syndrome

• XXY sex chromosomes
• 1/800-1000 male births
• Greatly reduced male genitalia
• No sperm production no sex drive
• Some breast production
• Wide curvy hips

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Jacobs Syndrome

• XYY sex chromosomes
•  1/1000 male births
• Taller than average
• Normal to subnormal intelligence
• Worse than normal acne
• Dense body hair
• (2 of maximum security prison population)

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Superwoman Syndrome

• XXX sex chromosomes
•  1/2000 female  births
• Normal to slightly retarded intelligence
• Extra development of female secondary sex
  characteristics
• Fertile

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Polyploidy
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Meiosis and Fertilization

• Meiosis and fertilization are necessary for
  sexual reproduction
• Egg (n) Sperm (n) Zygote (2n)

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Spermatogenesis

• Spermatogenesis The production of sperm
• one successful meiotic division produces 4 sperm

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Sperm

• Sperm Structure smaller than the egg but capable
  of locomotion with its flagellum.

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Oogenesis

• Oogenesis the production of ova (eggs)
• One meiotic division produces 1 egg and 3 polar
  bodies.

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The Meiosis Square Dance
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Homologous chromosomes
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Prophase I
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Synapsis and crossing over
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Metaphase I -- Notice the synpasis
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Anaphase I
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Prophase 2 similar to mitosis Replication does
not occur between meiosis 1 and meiosis 2
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Metaphase 2
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Anaphase 2
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Telophase 2 chromosome number is now ½ of the
original
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Cytokinesis meiosis results in 4 daughter cells
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Answers to Homework
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Summary

• The diploid number (2n) of chromosomes is reduced
  by 1/2 to the haploid number (n)
• Eggs and sperm are formed
• Crossing Over occurslots of variation
• Variations rarely occur in MITOSIS
• Variations often occur in MEIOSIS

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Results of Meiosis

• Mitosis is associated with growth and
  asexual reproduction
• Meiosis is associated with sexual reproduction
• Spermatogenesis the production of sperm
• Produces 4 sperm
• Oogenesis the production of ova or eggs
• Produces one egg and three polar bodies