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12.1: Origins of Hereditary Science
Objectives
• Why was Gregor Mendel important for modern genetics?
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Why did Mendel conduct experiments with garden peas?
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What were the important steps in Mendel’s first experiments?
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What were the important results of Mendel’s first experiments?
Mendel’s Breeding Experiment
• Gregor Mendel
• A monk that did breeding experiments in the 1800s with the
_______________________________
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The science of __________________ and the mechanism by which traits are passed from parents to
_____________________ is called __________________.
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____________________________ is based on Mendel’s explanations for the patterns of heredity in
garden pea plants.
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Most of Mendel’s experiments involved crossing ______________ types of pea plants. In this case,
the words ___________ means “to mate or breed two individuals.”
Features of Pea Plants
• The garden pea plant is a good subject for studying heredity because the plant has:
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In the study of heredity, physical features that are inherited are called ____________________.
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A _____________is one of several possible forms of a character.
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The offspring of a cross between parents that have contrasting traits
is called a _________________.
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In garden pea plants, each flower contains both ___________
and ______________ reproductive parts. This arrangement allows the
plant to ___________________________, or fertilize itself.
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___________________________ occurs when ____________
from the flower of one plant is carried by insects or by other means
to the flower of _____________________________.
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Mendel cross-pollinated pea plants by removing
the _________________ from some of the flowers then
dusting the female parts with _________ from another plant.
Features of Pea Plants (cont.)
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The garden pea is a good subject for studying heredity
because it _________________________________ and
produces _______________________________.
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Thus, Mendel was able to compare several results for each
type of cross and collect repeated data.
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Collecting repeated data is an important scientific method.
Checkpoint
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Who is called the father of genetics?
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What did he study?
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Why?
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What is the difference between self and cross pollination?
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What is a hybrid?
Mendel’s First Experiment
• A ______________________ is a cross that is done to study _________ pair of contrasting traits.
• Ex.: Crossing a plant that has purple flowers with a plant that has white flowers.
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Mendel’s first experiments used monohybrid crosses and were carried out in three steps.
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Each step involved a new generation of plants. A _________________ is a group of offspring from
a given group of parents.
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Plants that _______________ for several generations produce offspring of the same type. Such a
plant is said to be _______________________ for a given trait.
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The first group of parents that are crossed in a breeding experiment are called the
________________________ or P generation. The offspring of the P generation is called the first
filial generation, or ______________________.
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Mendel allowed the F1 generation to _______________________ and produce new plants. He
called this offspring the second filial generation, or _________________________.
Ratios in Mendel’s Results
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All of Mendel’s F1 plants expressed the __________ trait for a given character. The contrasting
trait seemed to have _____________________.
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The contrasting trait _______________________, however, in some of the F2 plants when the F1
plants were allowed to self-pollinate.
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For each of the seven characters that Mendel studied, he found a similar _______ ratio of
contrasting traits in the F2 generation.
Checkpoint
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What are two reasons garden peas good to study heredity?
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What is a monohybrid cross?
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What is true breeding?
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How are the p, f1 and f2 generations related?
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Which generation does the recessive trait disappear and which generation does it reappear?
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What is the ratio of the f2 generation?
Summary
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Modern genetics is based on Mendel’s explanations for the patterns of heredity that he studied in
garden pea plants.
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The garden pea plant is a good subject for studying heredity because the plant has contrasting traits,
usually self-pollinates, and grows easily.
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Mendel’s first experiments used monohybrid crosses and were carried out in three steps.
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For each of the seven characters that Mendel studied, he found a similar 3-to-1 ratio of contrasting
traits in the F2 generation.