Introduction to Genetics

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Introduction to Genetics

• Life Science

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Traits survey

• What causes these differences?

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Genetics - The study of heredity (how traits are
passed on) Traits are determined by genes found
on DNA
or
x

or
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The study of heredity started with the work of
Gregor Mendel and his pea plant garden
Mendel was an Austrian Monk that lived in the
mid 1800s
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Mendel noted that the size of pea plants varied.
He cross-bred these pea plants to find some
surprising results.
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Mendels cross between tall pea plants yielded
all tall pea plants.
X

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His cross between small pea plants yielded all
small pea plants.

X
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Mendels cross between tall pea plants and small
pea plants yielded all tall pea plants.
x

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Mendel then crossed these second generation tall
pea plants and ended up with 1 out 4 being small.
x

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Mendels work led him to the understanding that
traits such as plant height are carried in pairs
of information not by single sets of information.
Hereditary information (DNA) is carried in
Chromosomes!
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DNA

• DNA is found in all living cells
• It controls all functions
  inside a cell
• DNA stores all the genetic
  information for a
  living organism
• Single cell like an amoeba
• Multi cell like a human

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Genetics

• Small sections of DNA are responsible for a
  trait. These small sections are called
  Genes.
• Gene - A segment of DNA that codes for a specific
  trait
• Come in different versions
• Trait - A characteristic an organism
  can pass on to its offspring
  through DNA

Gene
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Genes

• Genes come in different versions
• Dominant - A gene that is ALWAYS expressed and
  hides others
• Recessive - A gene that is only expressed when a
  dominant gene isnt present (hidden)

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Alleles- a version of a gene

• All organisms have two copies of each gene (one
  from female, one from male)
• Homozygous- Two copies of the same gene
• Heterozygous - Two different genes

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Dominant and Recessive Genes
Widows Peak

• A dominant gene will hide a recessive gene!
• Example
• A widows peak is dominant, not having a widows
  peak is recessive.
• If one parent contributes a
  gene for a widows peak, and the
  other parent doesnt, the off-
  spring will have a widows peak.

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Example

• A Widows Peak, dominant trait, would be
  symbolized with a capital W, while no widows
  peak, recessive trait, would be symbolized with a
• lower case w.
• Father - No Widows Peak - w
• Mother - Has a Widows Peak - W

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Example

• For the widows peak
• WW - has a widows peak Homozygous dominant
• Ww - has a widows peak Heterozygous
• ww - no widows peak Homozygous recessive

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Genotype vs Phenotype

• Genotype- Genes you have
• Ex WW, Ww, or ww
• Phenotype- physical features SHOWN
• Ex
• WW? Widows peak
• Ww? Widows peak
• ww? NO widows peak

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Example

• Since Herman has no widows peak, he must be
  ______, since Lilly has a widows peak she could
  be EITHER ______ or ______.

ww
WW or Ww
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Punnett Square

• Punnett Square - A tool we use for predicting the
  traits of an offspring
• Letters used as symbols to represent genes
• Capital letters dominant genes
• Lower case letters recessive genes
• Genes always exist in pairs

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Punnett Squares

• We can use a Punnet Square to determine what
  pairs of genes Lilly has

• A Punnet Square begins with a box 2 x 2
• One gene is called an allele
• One parents pair is split into alleles on top,
  the other along the side
• Each allele is crossed with the other allele to
  predict the traits of the offspring

Assume Lilly is heterozygous
Ww
Assume Herman is homozygous recessive
ww
W
w
Ww
ww
w
Ww
ww
w
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Punnett Squares

• Notice that when Lilly is crossed with Herman, we
  would predict that half the offspring would be
  Ww, the other half would be ww
• Half Ww, Heterozygous, and will
  have a widows peak
• Half ww, Homozygous, and
  will not have a widows peak

W
w
Ww
ww
w
Ww
ww
w
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Try it yourself!

• Create a punnett square assuming Lilly is
  homozygous dominant (WW)

W
W
What is the chance of the offspring having a
widows peak?
w
w
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Try it yourself!

• All of the offspring will have a widows peak!

W
W
Ww
w
Ww
100
Ww
w
Ww
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Genetics

• Recall that Herman and Lilly had another
  offspring, Marylin. She had NO widows peak.

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Genetics

• So which is true? Is Lilly homozygous dominant
  (WW) or is she heterozygous (Ww)?

W
W
W
w
Ww
w
Ww
Ww
ww
w
Ww
w
Ww
Ww
ww
w
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Genetics
If Lilly were heterozygous, then 1/2 of their
offspring should have a widows peak, 1/2
shouldnt
If Lilly were homozygous, all of their children
will have a widows peak
W
W
W
w
Ww
w
Ww
Ww
ww
w
Ww
w
Ww
Ww
ww
w
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Genetics

• So, back to the original question. What color
  hair will the offspring of Prince Charming and
  Snow White have?

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Genetics

• Hair color is different from widows peak, no
  color is truly dominant.
• Dark brown and blond are homozygous traits
• Brown is dominant (BB)
• Blond is recessive (bb)
• Heterozygous conditions produce brown, red, etc.

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Genetics

• For Snow White to have brown hair she must be
  homozygous dominant, BB, a blond Prince Charmin
  must be homozygous recessive, bb.

B
B
Bb
b
Bb
Bb
b
Bb
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Genetics

• All the offspring from Prince Charming and Snow
  White will therefore be heterozygous, Bb, and
  since hair color is codominant.. all their
  children will have red hair.

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Cell Division (Meiosis)
1. A process of cell division where the number
of chromosomes is cut in half 2. Occurs in
gonads (testes, ovaries, stamens, etc)
3. Makes gametes (sperm, ova, pollen, etc)