Download 5.1 Mendel`s Work

7.2.d Students know plant and animal cells contain
many thousands of different genes and typically
have two copies of every gene. The two copies (or
alleles) of the gene may or may not be identical, and
one may be dominant in determining the
phenotype while the other is recessive.
Mendel
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Gregory Mendel was a priest in Europe who did an
experiment with pea plants
Heredity- passing of traits from parent to offspring
Trait- form of a characteristic like height or seed
color
Genetics- the study of heredity
Mendel’s Experiments
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Fertilization- when
the male and female
sex cells join
Pollination- when
pollen reaches the
pistil
Purebred- same 2
alleles for a trait
P generationParental generation
• Pea plants are self-pollinating
• Self-pollinating- pollen lands
on pistil of same flower
Crossing Pea Plants
 Gregor Mendel crossed pea plants that had different traits.
The illustrations show how he did this.
Mendel crossed 2 plants by taking pollen from one flower
and brushing it onto a flower of another plant
Mendel’s Experiments
 F1 generation- Offspring from the P generation
 F2 generation- Offspring from the F1 generation
 Mendel crossed one short with one tall pea plant
 All of F1 were tall and ¾ of the F2 were tall
Experiments With Other Traits
Key concept: “In all of Mendel’s crosses, only one form of
the trait appeared in the F1 generation. However, in the
F2 generation, the “lost” form of the trait always
reappeared in about one fourth of the plants.”
Dominant and Recessive Alleles
 Mendel demonstrated that factors
control inheritance of traits
 Those factors come in pairs: one
from the female (mom) and one
from the male (dad)
 Gene- factors that control a trait
 Alleles- different forms of the gene
 Key concept: “An organism’s traits
are determined by the alleles it
inherits from its parents. Some
alleles are dominant, while other
alleles are recessive.”
Dominant and Recessive Alleles
 Dominated allele- trait
that always shows up in
an organism when it is
present (Tt, TT)
 Recessive allele- trait that
is hidden whenever the
dominant allele is there
(tt)
Dominant and Recessive Alleles
 Hybrid- has 2 different alleles for a trait
 Before Mendel people thought that traits
were blended when there were 2 different
traits which was incorrect
 Traits are determined by individual
alleles inherited from each parent
 Capital letter represents dominate trait
 Lowercase letter represents recessive trait
 Because of Mendel’s work with genetics
he has been called the Father of Genetics
 What were the results of Mendel’s experiments,
or crosses?
 What controls the inheritance of traits in
organisms?