Transcript Punnett Squares - 7th Grade Science

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Create a Venn diagram comparing phenotype and
genotype: Use the words physical appearance, genetic
makeup, heterozygous, homozygous, describes an organism,
purple, tall, Pp, green,pp
Describe the difference between complete dominance,
incomplete dominance, and codominance
IFC: What is the first step in the scientific
method? A. make a hypothesis B. Ask a question
C. draw conclusions D. do background research
IFC: Chemists often make models of molecules using balls to show atoms and
sticks to show bonds. The models help them see what the molecules might
look like. What is a limitation of this model?
a. The models wont last as long as real molecules
b. The colors of the balls and sticks would not show the molecule’s real color
c. Real molecules are very small and complex, models could only
approximate what they look like.
d. Chemists are bad model makers so they would not be very useful
1.
2.
3.
In a cross between a yellow fish and a blue fish all of
the offspring are green. What kind of dominance is
this?
In some flowers blue and white are codominant.
Describe the phenotypes of each of these flowers
BB
WW
BW
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Today you will find a testable question for your science
project.
Log in to my website: akbrownscience.weebly.com
Choose the science fair tab. You will find links to sites with topic and
question ideas.
Look through the topic ideas and questions to help you get an idea
for your project – choose at least 3 today and write them in your
science fair log
Remember to write down the site you got the ideas from so you can
find them again
When you finish, begin looking for background research on your
project.
IFC
In Pea plants, round peas (R) are dominant over wrinkled peas (r).
1.
What is the genotype of a homozygous recessive pea plant?
2.
What is its phenotype?
3.
What is the genotype of a heterozygous pea plant
4.
What is its phenotype?
EQ: how are patterns of
inheritance studied?
• OBJ: I can predict patterns in heredity because I can create
Punnett squares and read pedigrees
• SC.7.L.16.2 Determine the probabilities for
genotype and phenotype combinations using
Punnett Squares and pedigrees.
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Probability is the likelihood that
a particular event will occur
It can be written as a:
1/4
Fraction ____
25%
Percent ____
1:3
Ratio ____
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A Punnett square is a model that
helps you find the probability of
different outcomes from genetic
crosses
http://www.arborsci.com/CoolStuff/CoinFlip.jpg
capital
There are 2 possible
outcomes:
HEADS
TAILS
The chance the coin will land on either one is:
1/2
50%
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1:1
______
_____
Alleles separate randomly just like a coin
flip. . . So can use probability to predict
outcomes of genetic crosses.
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If you toss a coin, what is the probability of getting
heads?
Tails?
If you toss a coin 6 times, how many heads and how
many tails would you expect to get?
Working with a partner, have one person toss a coin 6
times while the other person tallies the results on a
sheet of paper. Then, switch tasks to produce a
separate tally of the second set of 6 tosses.
1.
Assuming that you expect 3 heads and 3 tails in 6 tosses, how
do the results of your tosses compare? How about the results
of your partner’s tosses? How close was each set of results to
what was expected?
2.
Add your results to those of your partner to produce a total
of 12 tosses. Assuming that you expect 6 heads and 6 tails in
12 tosses, how close are these results to what was expected?
3.
If you compiled the results for the whole class, what results
would you expect?
4.
How do the expected results differ from the observed
results?
A Punnett square helps us predict the
probability that an offspring with a particular
genotype and phenotype will be produced
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I wish I could make a punnett
square
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To Make a Punnett square there are a few
simple steps to follow:
1) draw a box and divide it into four parts
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2) label the left hand side of the box with
the genotype of one parent
(R=Red, r=White)
R
r
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3) label the top of the box with the genotype of
the other parent
r
R
r
r
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4) In the middle boxes place 2 letters. One
letter comes from the left side and one
from the top
r
r
R
Rr
Rr
r
rr
rr
You now know the possible genotypes for the offspring
of these two parents
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The genotypes and phenotypes can be given a ratios,
fractions, or %s
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Complete and check with your shoulder partner
. A cross between a female with straight hair
(HH) and a male with curly hair (hh)
genotypes___________
phenotypes__________()
B
B
BB
b
Bb
b
Bb
bb
Black eyes (B) are dominant
over red eyes (b) in some
rats.
Make a cross between two
HETEROZYGOUS rats.
What are the possible genotypes of the offspring?
What are the possible phenotypes of their offspring?
(% and color)
75 % black eyes
25% red eyes
25% BB
50% Bb
25% bb
B
B
b
Bb
Bb
b
Bb
Bb
Make a cross between a
Homozygous Dominant rat
and a homozygous recessive
rat.
What are the possible genotypes of the offspring?
What are the possible phenotypes of their offspring?
(% and color)
100%
eterozygous
100% Black eyes
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2. A cross between
brown dog (bb)
a black dog (Bb) and a
genotypes_____________ (#BB:#Bb:#bb)
phenotypes____________ (#Black:#Brown)
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3. A cross between a yellow corn (Yy) and
another yellow corn (Yy) (y = white corn)
genotypes_________________
phenotypes_______________
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Write the possible outcomes for the guinea
pig offspring in the boxes
Cut out the appropriate guinea pig and glue
in the space
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Bellwork:
IFC
While scientists already know a great deal about DNA, they continue to learn more
about its role in genetics.What is the basis of scientists’ current understanding of
DNA?
A.
They guess how they think it works.
B.
They use combined empirical evidence from many scientists.
C.
They only use evidence that they have personally proven.
D.
They assume they already know all there is to know, even when evidence
contradicts that assumption.
3. Create a Punnett square to show a cross between a yellow corn (Yy) and another
yellow corn (Yy) (y = white corn)
genotypes_________________
phenotypes_______________
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You will pick 2 random celebrities
Their traits are listed on their picture – do not
destroy them I need them all day
Make 6 punnett squares to determine the
genotypes and phenotypes of their offspring