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Introduction to Genetics Life Science. Traits survey Why causes these differences?
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Transcript of Introduction to Genetics Life Science. Traits survey Why causes these differences?
Introduction to Genetics
Life Science
Traits survey
Why causes these differences?
Genetics - The study of heredity (how traits are passed on)
x =or
or
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
Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.
Mendel’s cross between tall pea plants yielded all tall pea plants.
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His cross between small pea plants yielded all small pea plants.
X =
Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants.
x =
Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small.
x =
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.
Hereditary information (DNA) is carried in Chromosomes!
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
GeneticsSmall 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 it’s offspring through DNA
Gene
Genes
There are two main 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 (hidden)
Dominant and Recessive Genes• 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 doesn’t, the off- spring will have a widows peak.
Widows Peak
Alleles
All organisms have two copies of each gene (one from female, one from male)
Homozygous- Two copies of the same geneHeterozygous - Two different genes
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
Example:For the widows peak:
WW - has a widows peak Homozygous dominantWw - has a widows peak Heterozygousww - no widows peak Homozygous recessive
Genotype vs Phenotype
• Genotype- Genes you haveEx: WW, Ww, or ww• Phenotype- physical features SHOWNEx: WW Widows peakWw Widows peakww NO widows peak
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
Punnett SquarePunnett 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
Punnett SquaresWe can use a “Punnet Square” to determine
what pairs of genes Lilly has
Ww ww
Ww www
w
W w
Assume Lilly is heterozygous
Assume Herman is homozygous recessive ww
• 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
Ww
Punnett SquaresNotice 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
Ww ww
Ww www
w
W w
Try it yourself!Create a punnett square assuming Lilly is
homozygous dominant (WW)
w
w
W WWhat is the chance of the offspring having a widows peak?
Try it yourself!All of the offspring will have a widows peak!
Ww
Www
w
W W
Ww
Ww
100%
GeneticsRecall that Herman and Lilly had another
offspring, Marylin. She had NO widows peak.
Genetics
So which is true? Is Lilly homozygous dominant (WW) or is she heterozygous (Ww)?
Ww
Www
w
W W
Ww
Ww
Ww ww
Ww www
w
W w
Genetics
Ww
Www
w
W W
Ww
Ww
Ww ww
Ww www
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