Life Science

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Life Science

• Genetics

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Genetics The study of heredity,
how traits are passed from parent to offspring
or
x

or
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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
• Trait - A characteristic an organism
  can pass on to its offspring
  through DNA

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

X

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.
The pairs are called alleles. They can be
dominant or recessive.
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Genetics

• Types of genes
• Dominant - A gene that is always expressed and
  hides others. Stronger form of the trait. Written
  as a capital letter. (D)
• Recessive - A gene that is only expressed when a
  dominant gene isnt present. Weaker form of ones
  traits. Written in lower case. (d)
• Alleles-One of the forms of a gene, may be
  dominant or recessive. (D or d)
• Genes always exist in pairs. DD, Dd, dd

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Genetics

• All organisms have two copies of each gene, one
  contributed by the father, the other contributed
  by the mother.
• Homozygous - Two copies of the same gene
• (DD, dd) purebred
• Heterozygous - Two different genes
• (Dd) hybrid

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• Dominant and Recessive Genes
• A dominant gene will always
  mask a recessive gene.
• widows peak dominant (W)
• no widows peak recessive (w)
• If one parent contributes a
  gene for a widows peak, and the
  other parent doesnt, the off-
  spring will have a widows peak.

Widows Peak
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Genetics

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

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Genetics

• 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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Genetics

• Since Herman has no widows peak, he must be ww,
  since Lilly has a widows peak she could be either
  WW or Ww
• Definitely ww Homozygous
• recessive
• Either Ww Heterozygous
• or WW Homozygous
  dominant

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Phenotype an organisms appearance. Example
Brown eyes, Blue eyes Genotype an individuals
combination of alleles for a trait. Example BB,
Bb, bb
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Genetics

• 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
W
w
Assume Herman is homoozygous recessive
ww
Ww
ww
w
Ww
ww
w
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Genetics

• 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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Genetics

• Another possibility is that Lilly might be WW,
  homozygous dominant.

Assume Lilly is homozygous dominant
WW
W
W
Assume Herman is homoozygous
ww
Notice that all the offspring are heterozygous
and will have a widows peak
Ww
w
Ww
Ww
w
Ww
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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

• Recall that Herman and Lilly had another
  offspring, Marylin. She had no widows peak,
  therefore, Lilly must be heterozygous.

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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.
• Brown and blond are the two, true traits
• Homozygous conditions produce either brown or
  blond hair
• Heterozygous conditions produce red hair

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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 chromasomes is cut in half 2. Occurs in
gonads (testes, ovaries, stamens, etc)
3. Makes gametes (sperm, ova, pollen, etc)