Genetics

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Genetics

• Standard S7L3 Recognition of how biological
  traits are passed on to successive generations

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

or
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The study of heredity started with the work of
Gregor Mendel and his pea plant garden Heredity
is study of passing traits from parents to
offspring.
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.
-Carrying the information are chromosomes.
-Chromosomes are made up of sections called
genes.
-Genes are made up of DNA
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EQ What were Mendels experiments with
inherited traits?

• 1st Generation Plants
• Dominant Trait

• 1st group of offspring from cross-pollination
• Trait observed in the 1st generation when parents
  with different traits are bred

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• Recessive Trait

• Trait that reappears in the 2nd generation after
  disappearing in the 1st generation when parents
  with different traits are bred

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• Mendels 2nd Experiment

• Recessive trait did not show up as often as the
  dominant trait
• Expressed as a ratio

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DNA

• D.N.A. - Deoxyribonucleic Acid
• Molecule made of
• 1. Deoxy Sugar
• 2. Combination of four nitrogen bases
• Either a. Guanine
• b. Cytocine
• c. Thymine
• d. Adenine

The sum total of combinations that these four
bases are capable of creating are greater than
all the stars visible in the night time sky
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DNA

• Nitrogen bases pair up
• Cytosine Guanine
• Thymine Adenine
• Pairing creates a ladder shape
• Angle of bonds creates a twist
• Ladder and Twist produces the famous
• Double Helix

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DNA
Nucleus
Cell

• DNA resides in all cells
• Inside the nucleus
• Each strand forms a chromosome

DNA
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DNA

• DNA is found in all living cells
• It controls all functions
  inside a cell
• It stores all the genetic
  information for an entire
  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
• Trait - A characteristic an organism
  can pass on to its offspring
  through DNA

Gene
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Genetics
Hair color is a perfect example of a trait
What color hair should their children have?
Prince Charming is blond
Snow White has dark hair
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Genetics

• There are three basic kinds of genes
• Dominant - A gene that is always expressed and
  hides others
• Recessive - A gene that is only expressed when a
  dominant gene isnt present
• Codominant - Genes that work together to produce
  a third trait

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Genetics

• Dominant and Recessive Genes
• A dominant gene will always
  mask a recessive gene.
• 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.

Widows Peak
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Genetics

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

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Genetics

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

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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
• Heterozygous - Two different genes

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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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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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EQ How are genes and alleles related to
genotype and phenotype?

• Phenotype
• Genotype

• An organisms appearance
• Hides the non-dominant alleles
• Entire genetic make-up of an organism
• The combination of genes for one or more traits

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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)