How are traits passed
from parents to
offspring?
Mendel and His Peas
• Why did Mendel perform crosspollination experiments?
• What did Mendel conclude about
inherited traits?
• How do dominant and recessive
factors interact?
Mendel and His Peas
• heredity
• genetics
• dominant trait
• recessive trait
Early Ideas About Heredity
• Heredity is the passing of traits from
parents to offspring.
• Gregor Mendel is known as the father
of genetics—the study of how traits
are passed from parents to offspring.
Mendel’s Experimental Methods
• Mendel studied genetics by doing
controlled breeding experiments with
pea plants.
• There are two types of pollination:
• self-pollination
• cross-pollination
Self-Pollination
Mendel’s Experimental Methods (cont.)
• When a true-breeding plant selfpollinates, it always produces offspring
with traits that match the parent.
• Mendel cross-pollinated pea plants
himself and recorded the traits that
appeared.
Cross-Pollination
Mendel’s Experimental Methods (cont.)
Why did Mendel perform
cross-pollination
experiments?
Mendel’s Results
• Once Mendel had enough truebreeding plants for a trait he wanted to
test, he cross-pollinated selected
plants.
• Plants are called hybrids if they come
from true-breeding parent plants with
different forms of the same trait.
First-Generation Crosses
Mendel’s Results (cont.)
hybrid
Science Use the offspring of two
animals or plants with different forms of
the same trait
Common Use having two types of
components that perform the same
function, such as a vehicle powered by
both a gas engine and an electric motor
Mendel’s Results (cont.)
• Mendel also cross-pollinated hybrid
plants.
• He observed that offspring of hybrid
crosses always showed traits in a 3:1
ratio.
Second-Generation (Hybrid) Crosses
Mendel’s Results (cont.)
Mendel recorded traits
of offspring from many
hybrid crosses.
Mendel’s Conclusions
Mendel concluded that two factors, one
from each sperm and one from each
egg, control each inherited trait.
What did Mendel conclude
about inherited traits?
Mendel’s Conclusions (cont.)
• A dominant trait is a genetic factor
that blocks another genetic factor.
• A recessive trait is a genetic factor
that is blocked by the presence of a
dominant factor.
Mendel’s Conclusions (cont.)
How do dominant and
recessive factors interact?
• Genetics is the study of how traits
are passed from parents to offspring.
• Mendel studied genetics by doing
cross-breeding
experiments with
pea plants.
• Mendel’s experiments with pea
plants showed that some traits are
dominant and others are recessive.
What method did Mendel use to
select which plants pollinated
other plants?
A. true breeding
B. self-pollination
C. cross-pollination
D. bees
How many dominant factors does
a purple-flowering pea plant
have?
A. 0
B. 1
C. 2
D. 1 or 2
What is the approximate ratio of
dominant to recessive expression
when both parents are hybrid?
A. 1 : 1
B. 2 : 1
C. 3 : 1
D. 4 : 1
Do you agree or disagree?
1. Like mixing paints, parents’ traits
always blend in their offspring.
2. If you look more like your mother than
you look like your father, then you
received more traits from your mother.