JIGSAW

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JIGSAW

• You will have five minutes to master your set of
  notes as YOU will be teaching the class your set!
  
• Take paper with you to your station so you can
  read, summarize and record the notes from your
  section.
• We will then come together as a class to discuss
  MENDELIAN GENETICS as understood by YOU!! ?
• Best teaching group will receive bonus points on
  their lowest daily grade..

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Mendelian Genetics

• The Work of Gregor Mendel
• Chapter 11.1

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What is Inheritance?

• Every living thing has a set of characteristics
  passed on to them from their parents genes!
• Genetics The scientific study of heredity

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Gregor Mendel

• 19th century Austrian monk
• Worked in monastery garden with pea plants
• Father of Genetics

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Some terms to know

• Fertilization male and female reproductive cells
  join to form a new cell diploid embryo
• Self-pollinating plants sperm cells (in pollen)
  fertilize the egg cells in the same flower
• True-breeding if plant self-pollinates,
  offspring produced is identical to itself

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Mendels Work

• Prior Knowledge
• Part of each flower produces pollen (male sperm)
  and part produces egg cells (female)
• Pea flowers are normally self-pollinating
• His peas were true-breeding (tall plants produce
  tall plants, short plants produce short plants,
  green seeds produce green seedsetc)

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Mendels Work

• Mendels Plan
• To produce seeds by joining male and female
  reproductive cells from two different plants
• To do this, self-pollination needed to be
  prevented
• So, he cut away pollen parts from one plant and
  dusted them on a different flower
  (Cross-pollination)
• NOW, seeds produced have two different parents
• He could now cross-breed plants with different
  characteristics and study the results

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Traits

• Mendel studied seven different pea plant traits
• Trait Specific characteristic that varies from
  one individual to another
• Ex. Seed color or plant height

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Mendels F1 Crosses on Pea Plants

• P (Parental generation)
• Original pair of plants
• F (Filial generation)
• Offspring - filia means son/daughter
• F1 is the first generation of offspring (from P
  generation parents)
• Hybrid offspring of crosses between parents
  with different traits

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Examples of hybrid crosses

• When one parents pod color was green and the
  other parents pod color was yellow, the
  offspring wasgreen.
• When one parent was round and one parents seed
  was wrinkled, the offspring wasround.

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Did the characteristics of the parent plants
blend in the offspring?

• NOT AT ALL!
• Each offspring carried on the character of
  only ONE parent!
• Green parent x Yellow parent Green offspring
• Round parent x Wrinkled parent Round offspring
• WHY?
• What conclusions can you make?

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Mendels Principles

• Principle of Biological Inheritance (unit
  characters)
• Principle of Dominance
• Principle of Segregation
• Principle of Independent Assortment

KNOW THESE FROM PAGE 272!!!!!!!!!!!
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Mendels 1st Conclusion

• Biological inheritance is determined by factors
  that are passed from one generation to the next
• GENES - chemical factors that determine traits
• ALLELES - different forms of a gene
• Ex The gene for plant height occurs in one form
  that produces tall plants and in another, short
  plants twp alleles

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Mendels 2nd Conclusion

• Principle of DOMINANCE
• States that some alleles are dominant and some
  are recessive
• Lets look at our example
• When one parents pod color was green and the
  other parents pod color was yellow, the
  offspring wasgreen.
• Which color is DOMINANT?

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Dominance

• An organism with a dominant allele for a form of
  a trait will always exhibit that form of the
  trait
• An organism with a recessive allele for a form of
  a trait will only exhibit that form when the
  dominant allele is not present

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Gene Expression

• Each form of the particular gene is an allele.
• Alleles can be either
• Dominant always show trait - T
• Recessive only see if dominant trait absent t
• In order to see the trait expressed, 2 alleles
  must be paired together (one from mom and one
  from dad)

T
Tt
t

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Mendels 3rd Conclusion

• Had the recessive alleles totally disappeared or
  were they still present in the offspring?
• P Green parent x Yellow parent
• F1 Green offspring ? do they still have
  recessive alleles?
• Mendel allowed the F1 hybrid plants to
  self-pollinate
• He crossed the F1 generation with itself to
  produce the F2
• F1 Green offspring x Green offspring
• F2 ???

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Results.

• Instead of all greenhe saw YELLOW too!

Even though the plants are both green, they can
have a yellow baby because the allele is still
present!
Gg
Gg
F1
G
g
G
g
? Segregation
gametes
GG
Gg
Gg
gg
F2
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Results of F1 Cross

• Mendel assumed dominant masked the recessive
  allele
• But, recessive alleles reappeared in F2!
• Example
• P Green parent x Yellow parent
• F1 Green offspring x itself
• F2 Green offspring and Yellow offspring
• Somehow the alleles for green and yellow had
  separated Segregation!!!!!
• Occurs during formation of gametes

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Principle of Segregation
As gametes form, gene pairs (homologous
chromosomes) separate. Each gamete contains one
gene for the trait.
When do gametes form? So when does segregation
occur?
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• Mendels Principle of Segregation
• Recessive characters hidden in the F1 progeny of
  two true-breeding strains, reappear in a specific
  proportion of the F2 progeny.

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Segregation
Homologous pairs separate! ANAPHASE!!
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Principle of Independent Assortment
As gametes form, gene pairs separate independentl
y of each other.
Alignment of one chromosome pair during
metaphase, does not affect alignment of another
pair. Random arrangement creates independent
assortment VARIATION!
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Independent Assortment
Genetic variation results since gametes carry
different genes.
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Independent Assortment

• Each plant in the F1 generation was formed by the
  fusion of a gamete carrying the dominant alleles
  (RY) with another gamete carrying the recessive
  (ry) alleles.
• Does this mean the two dominant alleles would
  always stay together?
• Or would they segregate independently so that
  any combination of alleles was possible?

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Principle of Independent Assortment

• Genes for different traits can segregate
  independently during the formation of gametes.
• Example genes for seed shape segregate
  independently of those for seed color