History of Genetics

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History of Genetics
Biology
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Genetics

• How characteristics are transmitted from parents
  to offspring

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Gregor Mendel
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Gregor Mendel (1822-1884)

• worked with Pisum satium (pea plant)

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Mendel studied 7 characteristics

• Flower color
• Flower position along stem
• Seed color
• Seed shape
• Pod shape
• Pod color
• Stem length

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Mendels Experiments

• Mendels First Cross
• Crossed purebred purple
• with purebred white
• P (parent) generation
• - F1 purple
• Crossed F1 hybrids
• produced F2 generation
• - 3 purple 1 white

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Mendels Ideas of Inheritance

• Alternative versions of genes (alleles) account
  for variations in inherited characters.
• each gene resides at a particular
  location of a chromosome and can exist in
  variable forms (two different forms for flower
  color)

P
Pp
p
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Mendels Ideas of Inheritance

• For each characteristic, an organism inherits
  two alleles,
• one from each parent.
• an organism is either homozygous (two of
  the same alleles) or heterozygous (two different
  alleles)

Homozygous
Heterozygous
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Mendels Ideas of Inheritance

• If the two alleles differ, the dominant allele
  is fully expressed and the recessive allele has
  no noticeable affect on appearance.
• heterozygotes express the dominant trait

RR
rr
Rr
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Mendels Law of Segregation

• The two alleles for each character segregate
  during
• gamete production.
• ovum/sperm get only one of the two
  alleles (haploid)

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P generation Phenotype Purple/White
Genotype PP/pp F1 generation
Phenotype Purple Genotype Pp F2
generation? Genotype/Phenotype can be
predicted using a Punnet Square
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Mendels Law of Independent Assortment
Each pair of alleles segregates into gametes
independently.
WH
wH
wh
Wh
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Mendels Law of Independent Assortment
Parental Genotypes GGWW ggww
gw
GW
Parental Gametes?
GgWw
F1 Genotypes?
gw
GW
Gw
gW
F1 Gametes?
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Beyond Mendel...
Different Types of Inheritance
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Complete Dominance Incomplete Dominance
Mendels Traits Snapdragon Color
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Incomplete Dominance
One allele does not dominant the other in the
heterozygous condition. Both alleles are
expressed but a new phenotype appears that is
intermediate.
RR
rr
Rr
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Codominance
Both alleles in the Heterozygous condition
are dominant.
CC
Cc
cc
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Codominance Multiple Alleles
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Incomplete Dominance
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