genetics life science heredity and traits
TRANSCRIPT
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Life Science
Genetics
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Genetics
The study of heredity, how traits are passed
from parent to offspring
x =
or
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 1800’s
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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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Mendel’s cross between tall pea plants yielded all
tall pea plants. His cross between small pea plants
yielded all small pea plants.
Mendels’ cross between tall pea plants and small pea
plants yielded all tall pea plants.
X =
x =
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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Mendel’s 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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DNA
D.N.A. - Deoxyribonucleic Acid
Molecule made of:
1. Deoxy Sugar
2. Combination of four nitrogen basesEither: 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
• DNA resides in all cells
– Inside the nucleus
• Each strand forms a chromosome
Cell Nucleus
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 organismcan pass on to it’s offspring
through DNA
Gene
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Genetics
Hair color is a perfect example of atrait
Prince Charming
is blond
Snow White
has dark hair
What color hair should their children
have?
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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 isn’t present
– Codominant - Genes that work together toproduce 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 doesn’t,
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 alower 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
Ww ww
Ww ww w
w
W w
Assume Lilly is heterozygous
Ww
Assume Herman is homoozygousrecessiveww
• A Punnet Squarebegins 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 theoffspring
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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 nothave a widows peak
Ww ww
Ww ww w
w
W w
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Genetics
Another possibility is that Lilly might be
“WW”, homozygous dominant.
Ww
Ww w
w
W W
Assume Lilly is homozygousdominant
WW
Assume Herman is homoozygousww
Ww
Ww
Notice that all theoffspring areheterozygous and will have a widows peak
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Genetics
So which is true? Is Lilly homozygous
dominant (WW) or is she heterozygous
(Ww)?
Ww
Ww w
w
W W
Ww
Ww
Ww ww
Ww ww w
w
W w
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Genetics
Ww
Ww w
w
W W
Ww
Ww
Ww ww
Ww ww w
w
W w
If Lilly were heterozygous,
then 1 / 2 of their offspring
should have a widows peak,1 / 2 shouldn’t
If Lilly were homozygous, all
of their children will have a
widows peak
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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 behomozygous recessive, “bb”.
Bb
Bbb
b
B B
Bb
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.
+
Cell Di ision
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Cell Division( Meiosis)
1. A process of cell
division where the
number of chromasomesis cut in half
2. Occurs in gonads
(testes, ovaries, stamens,
etc)
3. Makes gametes
(sperm, ova, pollen, etc)