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Introduction to Genetics
Chapter 11
The Work of Gregor Mendel
Section 11.1
The Experiments of Mendel
• Heredity is the delivery of characteristics
from parent to offspring.
• Scientific study of heredity is genetics.
• Austrian monk Gregor Mendel is the father of
genetics.
– Used pea plants (a model system)
The Experiments of Mendel
• The Role of Fertilization
– Fertilization is when male/female reproductive
cells join to make a new cell.
– Pea plants normally self pollinate “true breeding”
• Offspring identical
– Each plant had certain traits.
• These traits may vary between individuals.
The Experiments of Mendel
• Mendel crossed his “true breeding” plants to
see how traits would be expressed.
• He studied 7 different traits.
– Each had two contrasting characters.
• Offspring of a cross between different
parents are called hybrids.
The Experiments of Mendel
• Genes and Alleles
– Each original pair of plants is the
P generation.
– Offspring are F1 = first filial
– Genes are the factors (traits)
passed from one generation to
the next.
– Alleles are alternative forms of a
gene.
The Experiments of Mendel
• Dominant and Recessive Alleles
– Principle of Dominance (Mendel’s 2nd Conclusion)
• Dominant: trait will show if one allele present (masks
other allele)
• Recessive: need two alleles for trait to appear
Segregation
• Mendel didn’t stop with
crossing the parent plants.
• He thought: Where did the
recessive alleles go?
• He allowed all 7 kinds of
plants to self pollinate.
– Called these the F2
Segregation
• The F1 Cross
– The F2 plants showed the recessive alleles!
• ¼ of the plants showed this trait.
– How could this be?
• At some point, the recessive allele had separated from
the dominant.
• Another word for separation=SEGREGATION
– Alleles segregate during the formation of gametes.
Segregation
• During gamete formation,
the alleles for each gene
segregate.
• Each gamete carries only
one allele for each gene.