Transcript Gregor Mendel: The Father of Genetics

Gregor Mendel:
The Father of Genetics
Mendel’s Studies
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Austrian Monk
1800’s
Studied inheritance
Used pea plants
Mendel Clip
Mendel’s Work
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Dominant Trait – the observed trait that
covers another trait (written as an upper
case letter).
Recessive Trait – trait that can be covered by
a dominant trait (written as a lower case
letter).
Tall is dominant in pea plants, so the gene for
tallness is represented by an upper case “T”
and shortness is represented by a lower-case
“t”.
Alleles
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Allele - Alternative forms of a gene for
each variation of a trait (like T or t for
tallness in pea plants).
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During sexual reproduction, parents pass
on one allele for each trait to their
offspring.
Phenotype & Genotype
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Phenotype
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The way an organism looks and behaves
Ex. Tall, yellow, blond, blue eyes
Genotype
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The gene combination an organism contains
Ex. TT or Tt for tall
Homozygous – two alleles are the same, TT
Heterozygous – two alleles are different, Tt
Mendel’s Experiment
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Mendel crossed tall pea plants with short
plants. He expected the offspring to be
either a height somewhere between the
heights of the parent plants or to get some
tall offspring and some short offspring.
He was surprised that all of the offspring
were tall! What happened to the short
trait?
Mendel’s experiment
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Mendel then crossed two of the offspring
to see what their offspring would look like.
He was surprised to see the short trait
resurfaced! 1 out of every four plants was
short. So, he inferred that the short trait
was somehow “masked” by the tall trait in
the first generation.
Punnett Squares
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Punnett Squares are used to predict the
genotypes and phenotypes of the offspring
when the genotypes of the parents is
known.
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http://www.youtube.com/watch?v=d4izVAk
hMPQ
Let’s Draw What Mendel Did!
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Mendel’s original parent plants (this is called the
P1 generation) were each homozygous tall and
homozygous short.
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Let’s draw a Punnett Square to illustrate this
cross and the offspring that would result.
Let’s Draw What Mendel Did!
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Mendel’s original parent plants (this is called the
P1 generation) were each homozygous tall and
homozygous short.
TT
Tt
Tt
tt
Mendel’s Experiment
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Next, let’s draw another Punnett Square to
illustrate the cross between these
offspring and the possible genotypes of
their offspring.
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This is exactly what Mendel saw.
Mendel’s Experiment
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2)
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Tt crossed TT
Tt crossed Tt
Tt crossed tt