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Mendel
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How are traits passed from parents to offspring?
Focus Questions:
1. What were the results of Mendel’s experiments with pea plants?
2. What did Mendel conclude about inherited traits?
3. How do dominant and recessive factors interact?
• People used to believe in the idea of blending
inheritance (traits mixing like colors of paint).
Today, we know that heredity is more complex.
Heredity – the passing of traits from parents to
offspring.
• Genetics – the study of heredity (how traits are passed from parents to offspring).
Early Ideas About Heredity
1. What were the results of Mendel’s experiments with pea plants?
Lesson 1
• Gregor Mendel did experiments to disprove this idea of blending inheritance, and later became known as “the father of genetics”.
• Mendel used white and purple pea plants for his controlled breeding experiments.
Early Ideas About Heredity
1. What were the results of Mendel’s experiments with pea plants?
Lesson 1
• There are 2 types of pollination:
• self-pollination – pollen from one plant lands on the flower’s pistil of the same plant
• cross-pollination – when wind, water, or animals carry pollen from one plant to the pistil of another plant
1. What were the results of Mendel’s experiments with pea plants?
Lesson 1
• Mendel’s experiment:
1. Self-pollinated true-breeding (purebred) plants
a) Result: offspring were identical to parent plant (same exact traits)
1. What were the results of Mendel’s experiments with pea plants?
What happens when a true-breeding plant self-pollinates?
A. One of its offspring has the same traits as the parent.
B. Some of its offspring have the same traits as the parent.
C. All of its offspring have the same traits as the parent.
D. None of its offspring have the same traits as the parent.
One of i
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Some o
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a..
All of i
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Lesson 1
• 1st generation crosses:
1. Cross-pollinated different colors of true-breeding (purebred) plants
a) Purple + Purple = ?
b) White + White = ?
c) Purple + White = ?
* Fill in results from next slide
1. What were the results of Mendel’s experiments with pea plants?
Lesson 1
First-Generation Crosses Results
Lesson 1
• 2nd generation hybrid crosses:
* hybrid – different version of the same trait (the resulting offspring from crossing purple w/ white)
1. Cross-pollinated 2 purple hybrid plants
a) Purple hybrid + Purple hybrid = ?
* Fill in results from next slide
1. What were the results of Mendel’s experiments with pea plants?
Lesson 1
Second-Generation (Hybrid) Crosses
Lesson 1
• Mendel observed the same results when he cross-pollinated pea plants for other traits too.
• He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio.
2. What did Mendel conclude about inherited traits?
Mendel’s Results
Lesson 1
Mendel recorded traits of offspring from many hybrid crosses.
Lesson 1
Mendel concluded that 2 factors (1 from sperm and 1 from egg) control each inherited trait.
Mendel’s Conclusions
3. How do dominant and recessive factors interact?
Why were ratios important in Mendel’s work?
A. They showed that
heredity does not follow a
set pattern.
B. They showed that some
traits are never passed
on.
C. They showed the
relationship between two
different things.
D. They showed that some
recessive traits are really
dominant.
45
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eredi..
They show
ed that s
ome t.
..
They show
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They show
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.
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Lesson 1
• dominant trait: blocks another genetic factor.
– Written with a Capital letter
• recessive trait: blocked by the presence of a dominant factor.
– Written with a Lowercase letter
3. How do dominant and recessive factors interact?
What method did Mendel use to select which
plants pollinated other plants?
A. true breeding
B. self-pollination
C. cross-pollination
D. bees
true b
reedin
g
self-
pollinatio
n
cross
-polli
nation
bees
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45
How many dominant factors does a purple-
flowering pea plant have?
A. 0
B. 1
C. 2
D. 1 or 2
0 1 2
1 or 2
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45
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
1:01
2:01
3:01
4:01
0 000
45
