Transcript Genetics Listening Bingo

Genetics
The study of heredity - how traits are passed
from parent to offspring
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
Why did Mendel work with pea
plants?
• Fast to grow
• Easy to cross pollinate
• Two distinct forms for traits
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Tall or short
Yellow or green pods
Smooth or pinched pods
Yellow or green peas
Round or wrinkled peas
Colored or white seed coats
Side flowers or end flowers
Mendel’s cross between tall pea plants yielded all
tall pea plants. His cross between short pea plants
yielded all short pea plants.
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Mendel’s cross between tall pea plants and short pea
plants yielded all tall pea plants.
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Mendel then crossed these second generation tall pea
plants and ended up with 1 out 4 being short.
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Mendel’s Factors
• Mendel repeated this experiment
with many pea plants with many
different traits
• For each, he discovered that there
seem to be “factors” that
disappeared in one generation and
then reappeared in the next
• This went against the idea that an
organism is a blend of their
parents’ traits
Why was Mendel’s work so
important?
• Mendel worked at time when microscopes were
not very good and the cell theory was only just
being thought of
• When scientists understood DNA and
chromosomes, they understood how important his
work with pea plants was
Dominant vs. Recessive Genes
There are TWO basic kinds of
genes:
– Dominant - A gene that is
always expressed and hides
others
Represented with a capital
letter
– Recessive - A gene that is
only expressed when a
dominant gene isn’t present
Represented with a lowercase
letter
A Human Example
Eddie Munster
•
A dominant gene will always
mask a recessive gene.
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A “widow’s peak” is dominant,
not having a widow’s peak is
recessive.
•
If one parent contributes a
for a widow’s peak, and the
parent doesn’t, the offhave a widow’s peak.
gene
other
spring will
Latin Roots
All organisms have two copies of each gene: one
contributed by the father and the other contributed
by the mother.
Homozygous - Two copies of the same gene
“homo” - same
Heterozygous - Two different genes
“hetero” - different
Genotypes and Phenotypes
For the widow’s peak:
Genotypes: WW, Ww, or ww
Phenotypes: widow’s peak or no widow’s peak
WW - has a widow’s peak
Homozygous dominant
Ww - has a widow’s peak
Heterozygous
ww - no widow’s peak
Homozygous recessive
Eddie Munster’s Parents
Father = Herman - No Widow’s
Peak
Mother = Lilly - Has a Widow’s
Peak
What can you determine about a
genotype from a phenotype?
Since Herman has no widow’s peak, he must
be “ww”, since Lilly has a widows peak she
could be either “WW” or “Ww”
Definitely ww
Either Ww
or WW
Homozygous
recessive
Heterozygous
Homozygous
dominant
Punnett Squares
A Punnett Square is a tool used to predict the
possible gene combinations of the offspring.
In this case, we can work backwards…
• A Punnet Square begins
with a box 2 x 2
Assume Lilly is heterozygous
Ww
Assume Herman is homozygous
recessive
ww
• One gene is called an
“allele”
W
w
w
Ww
ww
w
Ww
ww
• 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
How can you tell?
So which is true? Is Lilly homozygous
dominant (WW) or is she heterozygous
(Ww)?
W
w
W
W
w
Ww
ww
w
Ww Ww
w
Ww
ww
w
Ww Ww
More Information Needed
Recall that Herman and Lilly had another
offspring, Marylin. She had no widow’s peak.
Therefore, Lilly must be heterozygous.
Incomplete dominance
• Two forms blend
Co-dominant Traits
• both forms are shown
Multiple Alleles
• more than two forms of a trait
Polygenic Traits
• Controlled by many genes