Transcript 11.1 The Work of Gregor Mendel

The Work of Gregor Mendel
Section 11.1
11.1 The Work of Gregor Mendel: The
“Father of Genetics”
• The delivery of characteristics from
our parents is called heredity; the
study of heredity is called genetics
• Mendel was born in the Czech
Republic in 1822; he studied science
and mathematics
• He worked in a monastery garden; it
was here where he did work that
“changed biology forever”
Mendel’s Pea Plants
• Mendel worked with self pollinating pea
plants (meaning offspring are identical to
parent)
– The traits, or specific characteristics,
of the plants for each generation were
the same
• One day, Mendel decided to cross
pollinate the plants (using two different
ones);
– The offspring of parents with different
traits are called hybrids
So what traits did Mendel’s hybrid’s show?
Mendel’s First Conclusion - Genes
• Mendel saw that for each trait, all of the
hybrid offspring had the characteristics of
only one parent
– “The other seemed to disappear”
• He concluded: an individual organism’s
characteristics are determined by factors
which are passed from one parental
generation to the next
– We know now these factors are genes
Genes & Alleles
• Each of the traits Mendel studied occurred
was controlled by one gene which
occurred in two contrasting ‘varieties’
• The variations produced different
expressions, or forms, of each trait
• Example: gene for plant height occurs in
one form that produces tall plants and
another form that produces short plants
• These different forms of the gene for
plant height are called alleles
How are different forms a gene
distributed to offspring?
• During gamete formation (meiosis),
alleles for a trait separate, or
segregate, from each other so that
each gamete carries only a single
copy of each gene
• The alleles are paired up again during
fertilization
Mendel’s 2nd Conclusion: The
Principle of Dominance
• He was amazed that the trait
that had “disappeared” in the
first (F1) generation reappeared
in the second generation (F2) –
he concluded:
• This principle states that some
alleles are dominant and others
are recessive.
Dominant and Recessive Traits
• The principal of dominance: some
alleles are dominant and some are
recessive
• An organism with at least one dominant
allele will show the dominant form of
the trait
• An organism will only show the
recessive trait if no dominant allele is
present (two recessive alleles)
What were the dominant and
recessive alleles in Mendel’s pea
plants?
•In Mendel’s experiments, the
allele for tall plants was
dominant and the allele for
short plants was recessive.
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