Transcript Mendel`s Experiments

Bell Work Activity
Copy onto your ‘Bell work’ paper the following question. Answer it and save it
to turn in. If you don’t know an answer, get a book and find it or review with a
friend. Blanks will count against you and wrong answers don’t help you.
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Complete: Word association. Use the description that best
describes the term. This is practice for your vocab quiz.
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Agenda:
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Discussion: Section 1: Gregor Mendel - Quick Lab: Mendel’s Ratios
Discovery Question
• How can uniqueness contribute to scientific
advancement?
Albinism
Freckles
These are examples of “Mendelian” traits.
It’s through the study of dominant-recessive
traits that scientists have been able to
unlock the mysteries of heredity…what this
chapter is dedicated to.
Do you have a physical trait or feature that
is unique to just you? Maybe something that
no one in your family has, or even more
unique, no one at school has? Share these!
They make you special.
Genetics…studying the stuff that makes us.
• Do you have any idea how you are made the way you are?
• You’re hair color, your eye color, your height…these are all a result
of how your parents genes interact with each other. You have had
an idea about this, but do you know how to predict it?
• What happens when something completely unexpected happens,
like disease?
• There are rules that govern this process…it’s not completely
unpredictable and because of our understanding of genetics
someday humans will know exactly how to custom make babies,
free of disease and designed to be genetically perfect.
• In this chapter you will start to learn the process.
What Happened Here?
Impacts, Issues: The Color of Skin
• Like most human traits, skin color has a genetic
basis; more than 100 gene products affect the
creation and influence of melanin.
Mom:
Mom: European
Dad: African American
Dad:
Mom: European
Dad: African American
Fraternal Twins
The Main Objective of Genetics
• If there is one thing you should learn is being
able to accurately predict the probability that
something will happen.
• More specifically, you should be able to predict
the likelihood that offspring from a mating will
have & or display particular traits.
Objectives Section 1
• Identify Gregor Mendel’s contribution to modern genetics.
• Differentiate between a character/gene and a trait.
• Describe why garden pea plants are good subjects for
genetic experiments.
• Summarize the three major steps of Mendel’s first
experiments.
• State the typical ratio of traits in Mendel’s first experiments.
Vocabulary
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Character
Trait
Hybrid (cross)
Generation
Mendel’s Breeding Experiments
• Recall, the science of heredity and the mechanism by
which traits are passed from parents to offspring is called
genetics.
• This field was undiscovered until an Austrian monk
named Gregor Mendel did breeding experiments in the
1800s with the garden pea plant.
• The point…
• Mendel is important to study because
• Modern genetics is based on Mendel’s explanations for
the patterns of heredity in garden pea plants.
Why Mendel’s The Bomb
• Just as in all sound scientific experiments,
Mendel practiced good techniques to
ensure that his experiments gave results
that were valid and useful.
– He made observations that made him ask
questions.
– He made predictions.
– He designed experiments with controls.
– He kept extremely accurate records of
data.
– He calculated results based upon the data.
– He proposed a theory to why everything
happened the way it did based upon his
results…
– And then he experimented some more!
Features of Pea Plants
• Mendel used pea plants as his subjects of his heredity
experiments.
• The garden pea plant is a good subject for studying
heredity because the plant has:
(Leave several lines below each heading.)
• 1. contrasting traits,
• 2. usually self-pollinates,
• 3. and grows easily.
• We’ll take a closer look at all of these topics.
Features of Pea Plants; Contrasting Traits
• Just like in modern genetics, Mendel had to study
the blending of traits that resulted from
fertilizations.
• The categories of traits that are inherited are
called characters.
• The different versions or forms of the characters
are called traits.
• The crossing between parents with unlike traits is
called a hybrid cross.
7 Characters with Contrasting Traits
Studied by Mendel
THE CHARACTERS
THE TRAITS
Contrasting Traits
Pea plant characters
Flower Color
Pea plant traits
Purple v White
Pea Color
Green v Yellow
Dog characters, (aka genes)
Hair Length
Dog traits
Short v Medium v Long
Hair color
Brown v Black v White v
This Applies to Other
Animals
as
Well.
Yellow…
Features of Pea Plants; Self-Pollination
• In garden pea plants, each flower contains both male
and female reproductive parts. This arrangement allows
the plant to self-pollinate = to fertilize itself.
• Cross-pollination occurs when pollen from the flower of
one plant is carried by insects or by other means to the
flower of another plant.
• Mendel cross-pollinated pea plants by removing the
male parts from some of the flowers then dusting the
female parts with pollen from another plant.
Cross-Pollination. The Process Mendel Used
Features of Pea Plants; Easy to Grow
• The garden pea is a good subject for studying heredity
because it matures quickly and produces many offspring.
• Why is this good?
• You can compare many offspring to get good data!
Mendel’s First Experiments
• Mendel’s first experiments used monohybrid crosses and
were carried out in three steps.
• A monohybrid cross is a cross that is done to study one
pair of contrasting traits.
– Crossing a plant that has purple flowers with a plant that has
white flowers is an example of a monohybrid cross.
• Each step involved a new generation of plants. A
generation is a group of offspring from a given group of
parents.
A Monohybrid Cross
A monohybrid cross
means to mate two
flowers.
In Mendel’s case he
chose two with
contrasting traits.
Parents = p generation
1st generation = F1
OFFSPRING
1st Generation
3 Steps Mendel’s First Experiments, continued
1st Step: Producing the Parental (P) generation
• Plants that self-pollinate for several generations
eventually produce offspring of the same trait. Such a
plant is said to be true-breeding for a given trait.
• The first group of parents that are crossed in a breeding
experiment are called the parental generation or P
generation.
• Mendel first produced true-breeding plants for the P
generation.
• Using true-breeding plants ensured that the traits being
studied were predictable (free of variables).
3 Steps Mendel’s First Experiments, continued
2nd Step: Producing the F1 Generation
• The true-breeding P generation were crosspollinated, producing offspring.
• The offspring of the P generation is called the
first filial generation, or F1 generation.
• He then recorded the traits of this generation.
3 Steps Mendel’s First Experiments, continued
3rd Step: Producing the F2 Generation
• Mendel allowed the F1 generation to selfpollinate and produce new plants.
• He called this offspring the second filial
generation, or F2 generation.
• He then recorded data about the F2 generation.
Visual Concept: Mendel’s Experiments
Mendel’s Results
• All of Mendel’s F1 (first generation) plants expressed the
same trait for a given character. The contrasting trait
seemed to have disappeared.
• The contrasting trait reappeared, however, in some of
the F2 plants when the F1 plants were allowed to
self-pollinate. But, most importantly, the traits appeared
in a predictable pattern.
• For each of the seven characters that Mendel studied,
he found a predictable 3-to-1 ratio of contrasting traits in
the F2 generation.
– This lays the groundwork for dominant and recessive traits…
Mendel’s Crosses and Results
Summary
• Modern genetics is based on Mendel’s explanations for the patterns
of heredity that he studied in garden pea plants.
• The garden pea plant is a good subject for studying heredity
because the plant has contrasting traits, usually self-pollinates, and
grows easily.
• Mendel’s first experiments used monohybrid crosses and were
carried out in three steps.
• For each of the seven characters that Mendel studied, he found a
similar 3-to-1 ratio of contrasting traits in the F2 generation.
Application
• Calculating Ratios
• Mendel obtained data from his experiments but
to get an idea of what the data was telling him
he had to work with the numbers.
• He chose ratios because using ratios is a way to
compare different values.
• Conduct the “Quick Lab” on page 270.
First Review: Calculating Ratios
• Compare the number of boys to girls by
Calculating the ratio of boys to girls in the class.
• Amount of one
(first value)
Amount of the other
(second value)
• Then simplify.
• Why simplify?
• Let’s say you have 45 sodas and 8 people. How
many sodas can each person have?...
• This let’s you know a lot of comparative info.
HW/CW
• Practice reproducing the ratios Mendel formed
by completing the “Quick Lab” on page 270.
– This is your first lab… 25 pts due 1/31