Download Rock-Around-the-Clock PDF document

Rock Around
the Clock
Genetics
✥
Learning the Strategy
The Rock Around the Clock strategy will help you focus on the main idea, significant points,
new insights, and important words or terms in a reading selection. You will work in teams to
record key points from your reading; then prepare a presentation. You’ll increase your reading
comprehension and vocabulary, and you’ll improve your team and presentation skills — requirements for real life on the job.
❂
Practicing the Strategy
1. Working with your group, write down all of the things you already know about your reading
topic.
2. Read the article or textbook section your teacher assigns to the group (silently or aloud).
3. While you are reading, highlight or mark the text to identify
•
•
•
•
•
Main idea
Key words and their meanings
Important points
Ah-ha’s (insights)
Unanswered questions
4. As a group, discuss the selection and notes you have made. Together, determine the main
idea, important points, key terms and meanings, ah-ha’s, and unanswered questions.
5. As a team, design a presentation to help the class understand your section of the text. Your
presentation should
•
•
•
•
Include the main idea, important points, key terms and meanings, ah-ha’s, and
unanswered questions from your reading.
Incorporate a variety of visual aids.
Be between two and five minutes in length.
Feature a designated presenter or presenters.
International Center for Leadership in Education
Genetics
Twins may or may not look alike. A baby looks
like its mother or father or both. A flower is
pink the first year and red the next. These and
other mysteries of heredity have been unraveled through the study of genetics.
In the past ten years, scientists have made advances by leaps and bounds compared to those
in earlier centuries. Before 1850 they thought
heredity was controlled by something in the
blood or the sap in a tree. Believing that hereditary traits were blended, they concluded that
a black cat mating with a white cat would produce only gray cats. Tall men who married short
women would bear medium-sized children.
Then an Austrian monk, Gregor Mendel (18231884), began experimenting with reproducing
plants. His findings in the basic principles of
genetics are still standing today. Mendel discovered that traits are inherited in separate factors (now called genes), and that the genes did
not combine in reproduction. Instead, some
genes are more dominant than others.
Mendel bred pea plants that bloomed in white
with peas that bloomed in purple. He wanted
to determine if the blending theory was correct. But he instead discovered that in the first
generation (F1), the white trait disappeared altogether. No light purple or purplish-white
flowers were evident.
Because the pea plants are self-fertile, he allowed
the first generation to self-pollinate. This time he
found that three plants were purple and one was
white. The ratio was 3:1. But where was this white
plant hiding in the first generation?
Mendel began repeating the experiment but
expanded it to cover 22 different strains of peas,
studying seven different traits. Every time the
second generation (F2) had the same 3:1 ratio.
He hypothesized that every trait is controlled
by two factors that are capable of being inherited. (See Punnett Square.)
He believed that if the factors are different, one
is dominant and one is recessive, and that dominant factor will mask or hide the recessive. He
went on to apply the mathematical laws of probability to the combinations of factors, thus laying the groundwork for the next 150 years of
science studies in genetics.
In the mid-1890s, Mr. Reginald Punnett studied science at Clifton College. He was mostly
interested in confirming Mendel’s findings
from forty years before. Punnett invented the
Punnett Square used by scientists and students
today to display the results of a genetic cross.
In a Punnett Square, the traits are mapped to
show the frequency of the factor for a specific
trait. Each trait has two parts. The combination
of parts makes that trait either homozygous (the
same, either dominant or recessive) or heterozygous (mixed — both dominant and recessive).
Using the same letter with lower and upper
cases, (Tt) the Punnett Square is a visual representation of the combination of genes that is
useful in determining how many times the
dominant and recessive genes will show up in
the next generation.
International Center for Leadership in Education
T
T
Hybrid plus Hybrid
Mendel’s Second Generation:
t
t
Purple
Pea
Purple
Pea
Purple
Pea
White
Pea
Hybrid plant that was result of white pea
bred with purple pea. The resulting
purple plant (hybrid) was allowed to self
pollinate (hybrid). This resulted in a 3:1
ratio or 75% dominant (purple) and 25%
recessive (white).
If the Parent Genotypes are:
the next generation will have:
Pure, dominant
Hybrid plus homozygous recessive
Hybrid plus hybrid
Homozygous recessive plus homozygous recessive
☛ 100% of offspring with that dominant trait
☛50% dominant trait, 50% recessive trait
☛ 75% dominant trait, 25% recessive trait
☛ 100% recessive trait
International Center for Leadership in Education
Rock
Around
the Clock
Sample Solution
Main Idea
Key Words and Meanings
Early discoveries in genetics unraveled the
mystery of living beings’ trait heredity.
Punnett Square – a mapping tool to show the
frequency of the factor for a specific trait
Homozygous – the same, either dominant or
recessive
Heterozygous – mixed, both dominant and
recessive
Important Points
Mendel discovered that traits are inherited in separate factors (genes) and that genes did
not combine in reproduction. Some genes are more dominant than others. In the Punnett
Square, the traits are mapped to show the frequency of the factor of a specific trait. Each
trait has 2 parts. The combination of parts makes that trait either homozygous or heterozygous. The Punnett Square allows us to represent the combination of genes that is useful in
determining how many times the dominant and recessive genes will show up in the next
generation.
Parent Genotypes
next generation
Pure, dominant
100% with that dominant trait
Hybrid plus homozygous recessive
50% dominant, 50% recessive
Hybrid plus hybrid
75% dominant, 25% recessive
Homozygous recessive plus homozygous recessive 100% recessive
Ah-ha’s (Insights)
Unanswered Questions
Mathematic laws of probability are
applied to combinations of factors
How is this research being applied in
genetic engineering today?
International Center for Leadership in Education
Rock
Around
the Clock
Main Idea
Key Words and Meanings
Important Points
Ah-ha’s (Insights)
Unanswered Questions
International Center for Leadership in Education