Fundamentals of Genetics

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Chapter 9

• Fundamentals of Genetics

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Why do you have your fathers eyes or your
mothers hair color?

• Genetics
• field of biology dealing with how
  characteristics are transmitted from one
  generation to the next
• Heredity
• transmission of characteristics from parent to
  offspring

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Gregor Mendel

• Austrian monk - 1866 Father of Genetics
• Worked with garden pea, Pisum sativum
• Studied statistics
• Observed 7 pea characteristics
• White or purple flowers
• Axial or terminal flower position
• Long (tall) or short stems
• Round or wrinkled seeds
• Yellow or green seeds
• Inflated or constricted pods
• Yellow or green pods

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Mendels work

• Controlled the process of pollination
• pollen grains from the anther of the stamen
  land on the stigma of the pistil (female repro
  organ)
• Peas self-pollinate
• transfer of pollen to stigma of the same flower
• Instead, Mendel cross-pollinated them
• Taking pollen from one plant to pollinate the
  stigma of another flower

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1. Removed the stamen (male reproductive part) to
   prevent self-pollination
2. Used the stamen from a tall plant and pollinated
   only flowers from other tall plants
3. Observed generations for 2 years to be certain of
   purebreds
4. Tall x Tall Short x Short
5. Crossed plants with contrasting traits
6. Tall x Short Short x Tall

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• P
• Parental generation
• F1
• 1st Filial generation (Offspring)
• F2
• 2nd Filial generation (next set of offspring
  from an F1 generation cross)

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• P1 Pure Tall x Pure Short T Tall
• TT tt t Short
• F1 Tall
• Tt
• P2 F1 Tall X F1 Tall
• Tt Tt
• F2 3 Tall 1 Short
• The lost trait reappears!
• TT Tt Tt tt

Only one trait showed
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• To get the results for the F2, do
• FOIL
• (Firsts, outers, inners, lasts)
• Always get
• 75 and 25 short or 31 whenever this type of
  cross occurred

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So what did he conclude?

• Concept of Unit Characters
• The inheritance of each trait is determined by
  units or factors that are passed on.
• - We know these as genes
• - These units occur in pairs. One from each
  parent

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• 2. Law of Dominance
• One factor masks the appearance of another
  factor and prevents it from showing.
• Dominant trait that must show if present (TT or
  Tt)
• Recessive trait that will only show if in the
  pure form (tt)
• Hybrid contains a dominant and a recessive
  trait (Tt)
• Allele The alternate genes for a given trait
  (Tall or short) genes occur in pairs

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• Law of Segregation
• - Paired factors separate during meiosis. - -
  - Each gamete receives only 1 factor of each
  pair.
• - A pair of factors is separated during the
  formation of the gametes.
• Law of Independent Assortment
• - Different pairs of alleles are passed to
  offspring independent of each other as long as
  the factors are not located on the same
  chromosome.
• - You inherited your eye color independently
  from your hair color.

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Lets get Crossing now!

• Genotype
• shows actual genetic makeup (Use symbols for
  genes)
• TT or Pure Dominant or homozygous dominant
• Tt or Hybrid or heterozygous
• tt or Pure Recessive or homozygous recessive
• Phenotype
• Tells appearance (describes the trait)
• Tall (if TT or Tt)
• Short (if tt)
• NO HYBRIDS HERE!
• Homozygous Pure for the trait (TT or tt)
• Heterozygous Hybrid or mixed for a trait (Tt)

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Probability

• The likelihood of a specific event occurring.
• Expressed as a decimal, fraction, percentage or a
  ratio.
• Probability
• number of times an event is expected to happen
• Number of opportunities for an event to happen
• What is the likelihood of being left handled in
  our class?
• Probability of left handed students X 100
• Total number of students in
  classroom

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• What is the probability of pulling out an Ace
  from a deck of cards?
• Probability
• 4 ( of Aces in a deck) x 100
• 52 ( of cards in a deck)
• 113 or 7.6 of the time
• What is the probability of getting heads or tails
  from a coin flip?
• Probability
• 11
• 50

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Punnett Squares

• Shows possible gene pairing and probability of
  each pairing
• There are two kinds of sperm /or 2 kinds of
  eggs depending on the genes that they carry.

Genes of 1 parent
T T
t Tt Tt
t Tt Tt
Phenotype ratio 100 Tall Genotype ratio
100 Tt (Hybrid)
Genes of 1 parent
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Possible crosses

• 1. Do the Punnett squares determine the
• Phenotype ratios
• Genotype ratios
• Trait Purple flower is dominant to white
  flower
• P Purple flower
• p white flower
• 1. PP x PP
• 2. PP x Pp
• 3. PP x pp
• 4. Pp x Pp
• 5. Pp x pp
• 6. pp x pp

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If you are right handed, how do you know if you
are homozygous right handed or hybrid?

• Test Cross
• Method used to find out if something (someone)
  is pure dominant or hybrid for a given trait.
• Cross them with a pure recessive for that trait.
  
• If the results come up with a recessive
  individual, then the parent was a hybrid

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• In Guinea pigs
• B Black coat b White coat
• Cross a BB guinea pig with a pure recessive (bb)
• Cross a Bb guinea pig with a pure recessive (bb)

Bb x bb
BB x bb
       
       
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How are two traits, not linked on the same
chromosome inherited (according to the Law of
Independent Assortment) inherited?

• Dihybrid crosses
• A cross between individuals that involve two
  pairs of contrasting traits.
• This is where your FOILing talents come in!
• Foil this!
• AaBb

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In pea plants Round seeds are dominant over
wrinkled seeds and Yellow seed coats are dominant
over green seed coats

• R Round Y Yellow
• r wrinkled y green
• P1 Cross two pea plants, homozygous for
  contrasting traits, what will result?
• RRYY x rryy

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RY RY RY RY
ry RrYy RrYy RrYy RrYy
ry RrYy RrYy RrYy RrYy
ry RrYy RrYy RrYy RrYy
ry RrYy RrYy RrYy RrYy
RY RY RY RY
ry
ry
ry
ry
Phenotype ratio 100 Round/Yellow Genotype
ratio 100 RrYy
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• F1 Cross
• Cross 2 plants from the F1 generation RrYy x
  RrYy
• Now FOIL RrYy to figure out the possible gametes
  for each parent plant
• RrYy
• RY
• Ry
• rY
• ry

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RY Ry rY ry
RY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
RY Ry rY ry
RY
Ry
rY
ry
9331
Phenotype ratio Round/Yellow
9/16 Round/Green 3/16 Wrinkled/ Yellow
3/16 Wrinkled/Green
1/16
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• Always a 9331 ratio when you cross 2
  dihybrids!!
• 31 ratio with a monohybrid cross!!!

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Is it always so black and white? What happens
when you cross someone with blue eyes and brown
eyes? Do you always get brown eyes?

• Incomplete dominance
• Two or more alleles influence the phenotype,
  resulting in an intermediate phenotype.
• Traits are blended
• When you cross a red and a white 400 flower, you
  get pink 400s

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• Do the Punnett square now to figure out the
  phenotype and genotype ratios
• R Red r white
• P1 Red x white
• F1 Cross Pink x Pink
• Genotype ratio
• Phenotype ratio

       
       
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A round face crossed with a square face results
in an oval shaped face.

• Show the cross which would result in an oval
  shaped face.
• 2. Cross two individuals who both have oval
  shaped faces

       
       
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Codominance

• Occurs when both alleles for a gene are expressed
  in a heterozygous offspring.

Roans
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• R Red R White or R Red W
  White
• B Black B White

R R
R RR RR
R RR RR
Phenotype ratio 100 Roan Genotype ratio
100 RR
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In Humans, Blood types and Sickle cell Anemia
exhibit codominance

• 1. Blood Types Exhibit Dominance, Codominance
  and Multiple Alleles
• Allele for A proteins on RBC Allele for B
  proteins on RBC. (Codominance)
• Alleles for A and B protein are Dominant to O
• There are three alleles to determine blood type
• A, B and O (Multiple alleles)

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A B gt o or IA IB gt i
Blood Type Donate to Receive from
A
B
AB
O
Blood Type Donate to Receive from
A A, AB A, O
B B, AB B, O
AB AB A, B, AB, O
O A, B, AB, O O
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Population   A B AB O
US Whites   39.7 10.6 3.4 46.3
African Americans   26.5 20.1 4.3 49
African   25 19.7 3.7 51.7
Navaho Native Am   30.6 0.2 0 69.1
Ecuadorian Am   4 1.5 0.1 94.4
Japanese   38.4 21.9 9.7 30.1
Russians   34.6 24.2 7.2 34
French   45.6 8.3 3.3 42.7
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• Sickle Cell Anemia
• Due to a gene mutation, normal red blood cells
  are not formed, instead, sickled shaped cells are
  produced
• HNHN All Normal RBC
• HNHS Carrier for SCA ½ the
• RBC are sickle shaped.
• Show some of the symptoms of SCA
• HSHS SCA All RBC will be sickle shaped.

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Distribution of Malaria
Distribution of SCA
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Advantage to being a Carrier

• People who are carriers for SCA, have a partial
  resistance to Malaria.
• People who are homozygous for SCA have a total
  resistance to Malaria though they usually die in
  childhood.
• 100,000/year
• 1.5 million/year die from Malaria