The Work of Gregor Mendel:

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The Work of Gregor Mendel

• Monohybrid, Dihybrid, Incomplete, Codominance,
  Multiple Alleles, Polygenic Traits

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Genetics study of hereditary

• Every living being- plant, animal, microbe or
  human being, has a set of characteristics
  inherited from its parent or parents.
• Genetics study of hereditary

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Gregor Mendels Peas

• Austrian Monk in charge of the garden, Studied
  peas

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What he knew

• fertilization- during sexual reproduction a male
  sperm (pollen) and female egg (ova) joined which
  produced a new cell, which began to develop into
  a tiny embryo encased within a seed.
• When Mendel took control of the garden, he had a
  garden full of self-breeding garden peas which
  were true-breeding

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True-breeding-

• pure genes, if allowed to self pollinate, these
  plants would produce identical copies of
  themselves.

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What he had to work with

• One stock of seeds produced Tall plants,
• One stock of seeds produced Short Plants,
• One line produced green Seeds,
• Another line produced yellow Seeds

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cross pollination

• Basis of Mendels Experiments Tall, Short, green
  Seeds, yellow seeds
• He wanted to cross breed these plants called
  cross pollination

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Genes and Dominance

• Mendel studied 7 different pea plant traits
• Trait a specific characteristic, such as seed
  color or height

1. Form of ripe seed Smooth Wrinkled
2. Color of seed albumen Yellow Green
3. Color of seed coat Grey White
4. Form of ripe pods Inflated Constricted
5. Color of unripe pods Green Yellow
6. Position of flowers Axial Terminal
7. Length of stem Tall Dwarf
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Mendel crossed these plants and studied their
offspring

• He called each of the original plants the P
  (Parental) generation

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F1 generation

• He called the offspring, F1 or first filial
  generation
• Filius and filia are the Latin words for son
  and daughter
• Therefore the child in the picture below is the
  F1 generation of those parents

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Hybrids

• The offspring of crosses between parents with
  different traits are called hybrids
• Ex toyota prius

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Hybrids in other areas

• Mythology Centaurs
• Biology Zeedonk, Liger

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So, what were the results? Did they have a
mixture of all the traits?

• NO, all the hybrids had the characteristics of
  only ONE of the parents.
• In each cross, the character of the other parent
  seemed to disappear!

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First Conclusion

• biological inheritance is determined by factors
  that are passed from one generation to the next
• Today, we called these GENES
• Different forms of a gene are called Allele

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Second conclusion Principle of Dominance

• P of D states that some alleles are dominant and
  others are recessive
• An organism with a dominant form will ALWAYS show
  the trait

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Mendels Findings

• Tall plant was Dominant and Short plant was
  recessive/
• Yellow seeds Dominant and green seeds are
  recessive

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Some common human dominant traits
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Segregation

• Mendel wanted to know what happened to the
  recessive traits. Did they disappear?
• He took the F1 generation and crossed them with
  one another and made the F2 generation

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F2 generation

• the recessive traits reappeared
• ¼ or 25 of all the plants had the recessive
  traits

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He concluded the

• F1 plants produced gametes (sex cells), the 2
  alleles segregated from one another so that each
  gamete carried a single copy of the gene
• In the F1 generation, each gamete had 1 copy of
  the Tall gene and one copy of the short gene.

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Genetics and Probability

• Probability the likelihood that an event will
  occur
• Coin toss 2 possibilities head or tails
• The probability or chances are equal, 1 in 2
  chance
• That is ½ or 50 chance
• If you flip a coin 3 times in a row what are the
  chances that you will get heads every time ½ x ½
  x ½ 1/8 1 in 8 chance of flipping heads 3
  times in a row!

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So what?

• The principles of probability are used to predict
  the outcomes of genetic crosses

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Punnett Squares

• the gene combinations that might result from a
  genetic cross can be determined by drawing a
  diagram known as a Punnett Square

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Very important terms to know!

• Homozygous 2 identical alleles (TT or tt)
  considered true-breeding
• Heterozygous 2 different alleles (Tt) considered
  Hybrids
• Phenotypes physical characteristics, like tall
  or short
• Genotypes genetic characteristics like TT, Tt,
  or tt

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Tutorial

• The figure represents a monohybrid cross of
  F1-hybrid plants.
• Both parent plants are heterozygous (Ss) for an
  allele that determines seed shape.
• Presence of the dominant allele (S) in homozygous
  (SS) or heterozygous (Ss) plants results in
  spherical seeds.
• Homozygous recessive (ss) plants have dented
  seeds.

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Setting up a Punnett square

• 1. Set up a 2 by 2 Punnett square.

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2. Write the alleles for parent 1 on the left
side of the Punnett square.

• Each gamete will have one of the two alleles of
  the parent.
• In this particular cross, half of the gametes
  will have the dominant (S) allele, and half will
  have the recessive (s) allele.

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3. Write the alleles from parent 2 above the
Punnett square.

• For this heterozygous parent (Ss), half of the
  gametes will have the dominant (S) allele, and
  half will have the recessive (s) allele.

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4. Fill the squares for parent 1.

• Fill each square with the allele from Parent 1
  that lines up with the row.

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5. Fill the squares for parent 2.

• Fill each square with the allele from Parent 2
  that lines up with the column.

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Interpreting the results of a Punnett square

• We now have the information for predicting the
  outcome of the cross.
• The genotypes in the four boxes of the Punnett
  square are each equally likely to occur among the
  offspring of this cross.
• We may now tabulate the results.

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Genotypes that resulted from this monohybrid
cross (Ss x Ss)

• 25 50 25
• homozygous heterozygous homozygous dominant
  dominant recessive

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Phenotypes that resulted from this monohybrid
cross (Ss x Ss)
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Independent Assortment Dihybrid Crosses

• 2 factor Cross
• Mendel crossed true breeding plants that
  produced only round yellow peas (RRYY) with
  plants that produced wrinkled green peas (rryy)
• All the F1 round yellow peas

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Showed that the allele for yellow and round peas
are dominant

• Provided the hybrid plants for the F1 cross to
  produce the F2 generation
• F2 RrYy
• Found a grand mix of traits proving that the
  genes practiced independent assortment meaning
  that the seed shape and color are independent of
  one another

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F2 results//

• 9331
• 9 yellow and round, 3 green and round, 3 yellow
  and wrinkled, 1 green and wrinkled

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Tutorial Dihybrid Crosses

• Determine all possible combinations of alleles in
  the gametes for each parent.
• Half of the gametes get a dominant S and a
  dominant Y allele the other half of the gametes
  get a recessive s and a recessive y allele.
• Both parents produce 25 each of SY, Sy, sY, and
  sy.

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1. Punnett square.

• Since each Parent produces 4 different
  combinations of alleles in the gametes, draw a 4
  square by 4 square punnett square.

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2. Place in Gametes from Parent 1

• List the gametes for Parent 1 along one edge of
  the punnett square.

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3. Place Gametes from Parent 2

• List the gametes for Parent 2 along one edge of
  the punnett square.

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4. Fill in Alleles from Parent 1

• Fill out the squares with the alleles of Parent
  1.

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5. Fill in Alleles from Parent 2

• Fill out the squares with the alleles from Parent
  2.
• The result is the prediction of all possible
  combinations of genotypes for the offspring of
  the dihybrid cross, SsYy x SsYy.

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Predicting the phenotype of offspring

• There are 9 genotypes for spherical, yellow
  seeded plants. They are
• SSYY (1/16)SSYy (2/16)SsYY (2/16)SsYy (4/16)

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Predicting the phenotype of offspring

• Two recessive alleles result in green seeded
  plants.
• There are 2 genotypes for spherical, green seeded
  plants. They are
• SSyy (1/16) Ssyy (2/16)

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Predicting the phenotype of offspring

• Two recessive s alleles result in dented seeded
  plants.
• There are 2 genotypes for dented, yellow seeded
  plants. They are
• ssYY (1/16) ssYy (2/16)

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Predicting the phenotype of offspring

• A ssyy plant would be recessive for both traits.
• There is only 1 genotypes for dented, green
  seeded plants. It is
• ssyy (1/16)

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A phenotypic ratio of 9331

• A phenotypic ratio of 9331 is predicted for
  the offspring of a SsYy x SsYy dihybrid cross.

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Summary of Mendels Principles

• Inheritance of biological characteristics is
  determined by genes passed from parents to
  offspring
• In cases where 2 alleles exist 1 is dominant, 1
  is recessive
• Each adult has 2 copies of each gene, one from
  each parent
• Genes for different things usually segregate
  independently

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Beyond Dominant and Recessive alleles

• some alleles are neither dominant nor recessive
• many traits are controlled by multiple alleles or
  genes

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• If Mendel were given a mommy black mouse a
  daddy white mouse asked what their offspring
  would look like, he would've said that a certain
  percent would be black the others would be
  white.  He would never have even considered that
  a white mouse a black mouse could produce a
  GREY mouse!  For Mendel, the phenotype of the
  offspring from parents with different phenotypes
  always resembled the phenotype of at least one of
  the parents. 
• In other words, Mendel was unaware of the
  phenomenon of INCOMPLETE DOMINANCE.

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1. Incomplete Dominance

• F1 Generation red flower (RR) and white flower
  (rr)
• F2 Generation pink (Rr)
• With incomplete dominance, a cross between
  organisms with two different phenotypes produces
  offspring with a third phenotype that is a
  blending of the parental traits. 

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2. Codominance

• Both alleles contribute to the phenotype
• ex chicken feathers
• In COdominance, the "recessive" "dominant"
  traits appear together in the phenotype of hybrid
  organisms.
• I remember codominance in the form of an example
  like so
• red x black ---gt red black spotted

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• In horses, gray horses (GG) are codominant to
  white horses (WW).  The heterozygous horses(GW)
  is an appaloosa horse (a white horse with gray
  spots on the rump and loins). Cross a white horse
  with an appaloosa horse.

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• GenotypeGW (2) WW (2)
• Phenotype
• appaloosa (2)
• white (2)

W W
G W
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Polygenic traits

• interactions of several genes
• Ex eye color, skin color

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3. Multiple Alleles

• more than two alleles that code for the trait
• Ex coat color of rabbits

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Blood Types

• A and B are codominant
• AA Type A
• BB Type B
• AB Type AB
• A and B are dominant over O
• AO type A
• BO type B
• OO type O

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1

• Show the cross between a mother who has type O
  blood and a father who has type AB blood.

O O
GENOTYPES
- AO (2) BO (2) - ratio 11
A B
PHENOTYPES
- type A (2) type B (2) - ratio 11
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2

• Show the cross between a mother who is
  heterozygous for type B blood and a father who is
  heterozygous for type A blood
• Genotype
• Phenotype

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A O
B O
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3

• Show the cross between a mother who is homozygous
  for type B blood and a father who is heterozygous
  for type A blood
• Genotype
• Phenotype

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Show the cross between a mother who is homozygous
for type B blood and a father who is heterozygous
for type A blood

• Genotype
• AB (2), BO (2)
• ratio - 11
• Phenotype
• Type AB (2)
• Type B (2)
• ratio 11

B B
A O
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