Chapter 10 Notes

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Chapter 10 Notes

• Mendel and Meiosis
• Remember, you can take the practice quiz at
  http//www.glencoe.com/qe/science.php?qi2495
  change to chapter 10
• Punnett square tutorial
•  http//www.borg.com/lubehawk/psquare.htm
•  Practice problems at bottom of page...
•  
• More of the same
•  http//www.biology.arizona.edu/mendelian_genetics
  /problem_sets/monohybrid_cross/01t.html
•  
• Mouse crossing lab
•  http//www.explorelearning.com/index.cfm?methodc
  Resource.dspDetailResourceID35
•  
• Eye color crossing
•  http//www.athro.com/evo/inherit.html
•  
•  Genetics glossary for background words not
  understood
•  http//genetics.about.com/?oncetruegenetic

Links to Genetics info.
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10-1 Mendels Laws of Heredity

• Gregor Mendel 19th Century Austrian monk, bred
  pea plants to study their inheritance.
• Heredity passing of characteristics to
  offspring.
• Genetics branch of biol. studying heredity.
• Traits inherited characteristics, predictable
  based on parent traits.
• Sexual reproductiontraits from both parents, via
  male and female sex cells (gametes). Peas male
  gamete is pollen grain from anther, female is
  ovule in pistil. Pollination transfer of pollen
  to pistil, fertilization uniting male/female
  cells to make seed.
• Pea reproduction allowed him to precisely
  determine the parents, cross pollinate, etc.
  Careful guy only studied one trait at a time,
  analytical.
• Tall plants had been tall for many generations,
  vice versa for short, etc. Plants were true
  breeding (homozygous).

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• Crossbred tall and short (P1 generation) to make
  hybrids (offspring of parents with
  traits-tall/short).
• Monohybrid cross, differed only in height.
• Cross resulted in only tall plants (F1 gener.)
• Crossed these with their own kind (hybrids) and ¾
  were tall and ¼ were short (F2 gener.).

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• M. determined each trait he measured was
  determined by two factors that control each of
  its traits (unit factors).
• Now know that these are genes on chromosomes.
  Two alleles (one from each parent) that control
  each trait.
• Could have alleles for tallness (T) or shortness
  (t) in any pair (TT,Tt, tt)
• When tall/short crossed, only tall resulted, ie.,
  tallness is dominant over shortness, and if they
  are together, will cover over it. We say
  shortness is recessive.

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• Plant have TT alleles both for tall tall plant.
• Plant have tt alleles both for short short
  plant.
• Plant Ttallele for both (T covers t) Tall
  plant.
• Use same letter for alleles of same trait,
  dominant is caps, dominant goes first.
• Looking at prev. F1 cross, each parent had 1 dom.
  and 1 reces. trait. Produced sex cells with a
  random allele of possible types expressed. When
  offspring, results in four possible combinations
• Alleles separate/segregate during formation of
  sex cells and randomly combine Law of
  Segregation. (see Fig.10.5).
• How organism looks Phenotype. Plant is tall.
• The gene combo it contains Genotype. Plant may
  be TT or Tt (and still have phenotype of
  tallunderlying stuff).
• Organism is homozygoussame alleles (TT or tt).
• Organism heterozygousdiff.alleles (Tt is het.zy.
  for height).

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• Mendel also crossed two traits at once (dihybrid
  cross). Interested in whether traits inherited
  together or separately. Round (R) versus wrinkled
  (r) seeds, and yellow (Y) versus green seeds (y).
• P1Crossed RRYY with rryy.
• F1All had dominant traits (Roundyellow).
• F2Let self-pollinate and got lots of everything.
  Ratio 9RndYell 3RndGrn 3 WrkdYell 1 WrkdGrn.
• Law of Independent Assortment Genes for diff.
  traits are inherited independently of each other.

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• 1905, Reginald Punnett, Punnett square as
  shorthand way to find genotype of crossrandom
  assortment give possible offspring and ratio of
  possibilities (ex., p.266).
• Listing possible allele combos down side for one
  parent, across top for other. With dihybrids,
  must list all 4 possible allele for each, so will
  be 16 squares. Fill in grid from top/side
  alleles to show offspring possible and ratio they
  will appear in (remember genotype and phenotype
  arent same thing).
• Punnett squares show probability, not certainty.
  Like flipping coin, chances may be ½, but
  flipping 10X wont always get 5 heads. Some
  variation, but will tend toward ½, especially as
  greater numbers are used.

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Meiosis 10-2

• Normal cells contain chromosomes in pairs (one
  chr.from each parent that correspond) Diploid
  cell (normal state) (2n). Remember, Mendel said
  peas had two factors for each trait. One allele
  on each chromosome for that trait.
• Regular mitosis division, cell doubles all of its
  DNA in interphase (temporarily 4n) and then
  divides into two cells of 2n each.
• Organisms produce gametes via meiosis a special
  sex cell division. Doubles all info (temp. 4n),
  then divides twice to make 4 sex cells (gametes).
  Each gamete contains only one of each kind of
  chromosome. These are haploid cells, contain
  haploid or n number of chromosomes. (Only want ½
  the info from each parent to make a new
  organism).
• Organisms have set numbers of chromosome for
  species (not necessarily related to their
  complexity). Vary widely (see Table 10.1, p.270).
• Two chromosomes of each pair determine
  appearance. Each has one allele of each paired
  trait (not necessarily identical). Homologous
  Chromosomes.
• Meiosis keeps 2n as standard cell size, via two
  divisions

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• Meiosis occurs in specialized gamete- producing
  cells of parent org. bodies.
• Two separate divisions Meiosis I (beginning with
  diploid cell) and Meiosis II (ending with 4
  haploid cells).
• Sex cells-gametes Malesperm Femaleeggs.
  Fertilization results in a single zygote, the 1st
  cell of the new organism, that can then increase
  via mitosis.
• Using production and fusion of haploid cells for
  reproduction is sexual reproduction.
• Meiosis similar to mitosis mechanism, but differs
  in certain critical aspects.

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Meiosis!
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• Interphase- Just as in mitosis replicates its
  DNA to make two sister chromatids joined
  w/centromeres (remember, these identical
  copiesalso has a homologous one (with its own
  copy) that has other allele on it.
• Each homologous set of two (with copies) joins
  closely to make four part TETRAD. (seePro/Met1,
  p.273).
• Two homologous chromosomes, each containing two
  sister chromatids.
• Pair tightly and some homologous information is
  exchanged crossing over.
• In humans, usually 2-3 crossovers per hom.pair in
  Pro.1.

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• Crossing over isnt entirely a mistake results
  in better genetic variety in organism, like
  indep. assortment.
• Metaphase I same, except two homologous sets are
  lined up side by side (XX) and split apart from
  each other.
• Anaphase I chromatid pairs still bonded b/c
  split homologous pairs, not centromeres holding
  sister pairs apart.
• TelophaseI reverse of prophase but ½ info with
  still doubled pairsshort interphase, goes
  straight to 2nd division.

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• Meiosis II Identical to steps in regular
  mitosis. Sister chromatids are split, but since
  homologous chromosomes were already separated,
  this leaves things at haploid conditions with 4
  sex cells.
• Meiosis is goodGenetic Recombination due to
  random chromosome assortment (additional from
  crossing over). Introduces great variation in
  organisms, which helps survival of whole group,
  raw material for evolution.
• Meiosis is physical basis for Mendels results
  explains his observations.

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• Meiosis (and mitosis) generally occur remarkably
  error-free. But sometimes mistakes.
• NondisjunctionFailure of chromosomes to separate
  properly (both chromosomes go to one pole and
  none to another).
• Trisomy one extra chromosome (one extra came
  this way). Humans extra 21st Chro. 47 total
  Down syndrome. Extra chro. often survivelacking
  dont (not enough info).
• Monosomy lacking one Chr. (one of ours went the
  other way). Usually dont survive in
  humans/higher animals (see above). Exception
  Turner syndrome. Human females with single X
  chromosome instead of two.
• Triploidy or Tetraploidy Total failure of
  chromosomes to separate at all. On one side,
  plus normal haploid produces three sets of info
  3n, instead of normal 2n. If both do that,
  tetraploidy 4n (4sets instead of 2). So-called
  polyploids seldom occur in animals (usually die).
  In plants can occur. Flowers and fruits may be
  larger or healthier.
• Thus desirable as crop plants. Banana plant
  (sterile herbaceous plant), day lily.
  Tetraploidwheat, triploidapples,
  polyploidmums.
• Meiosis nondisjunction usually a tragic mistake,
  but can be turned to human advantage in
  particular cases. (actually chemicals to promote
  this for plant breeding purposes).

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The End

• of this onion cell. Radiation has caused the
  spindle apparatus to fail to separate chromosomes
  properly