Download 6.1-BIO-GEN-gentics.punnetsquares

Independent Research!
Big picture goal… you will be able to conduct
your own research after high school!
Today we will be learning about how traits can be
predicted using punnet squares.
Take notes to be able to answer the following
questions:
“Independent Research: Punnet Squares”
1.
2.
3.
4.
Who is Gregor Mendel?
TIP: Use index to
What is a DOMINANT trait?
start!
What is a RECESSIVE trait?
Describe at least 3 traits were found to be either
dominant or recessive in pea plants.
How do we know
about traits ?!
It’s all because of
Gregor Mendel!
Video clip
Gregor Mendel
• Gregor Mendel was a priest who liked to garden
• He grew pea plants and found a way to crosspollinate them
cross-pollinate = to
combine pollen and eggs
from two different flowers
Mendel’s Contributions
1. What is a gene?
Genes = pieces of
DNA that pass on
traits
2. What is an
allele? different
forms of a gene
are called alleles
3. Where do alleles come from?
One allele for each gene is passed on from each parent
Mendel’s Law of Dominance
For every gene, there is 1 dominant allele
5. What is the difference between dominant
and recessive alleles?
• Dominant alleles = capital letters (B)
• Recessive alleles = lowercase letters (b)
* If a dominant allele is present, it will always be
shown!
Naming Traits
6. What is homozygous?
If both alleles are the same
(both capital or both lowercase)
Purebred
7. What is heterozygous?
If the two alleles are different
(one capital and one lowercase)
Hybrid
→ RR or rr
Homozygous
“Same zygote”
→ Rr
Heterozygous
“Different zygote”
Predicting Traits
8. What is a punnet square?
We can predict the results of a genetic
cross using a Punnett Square!
Parent #2 alleles
Draw this square in your notes
Parent #1 alleles
Multiply traits to
get 4 possible
offspring results
Punnett Squares!
Punnett Squares!
B
b
b
b
Punnett Squares!
B
b
B
b
B
b
Punnett Squares!
B
b
b
B
b
b
B
b
Punnett Squares!
B
b
b
Bb
bb
b
B
b
Punnett Squares!
B
b
b
Bb
bb
b
Bb
bb
Punnett Squares!
B
b
b
Bb
bb
b
Bb
bb
9. How do punnet squares
show fertilization? Sperm or
Sperm or
Egg Cell +
B
b
b
Bb
bb
b
Bb
bb
Egg Cell +
9. How do punnet squares
show fertilization?
B
b
4 possible
zygotes!
b
Bb
bb
b
Bb
bb
Predicting Traits
Let’s look at the trait of rolling your tongue:
1. First assign the trait a letter: Let’s choose “r”.
2. Then assign alleles:
• Tongue rollers = R (dominant)
• Non-tongue rollers = r (recessive)
If your genes are RR or Rr  you can roll your tongue
If your genes are rr  you cannot roll your tongue.
Predicting Traits
What would happen if a tongue roller had children
with a non-tongue roller?
RR
x
rr
=
?
Parent #1 trait
Parent #2 trait
R
R
r
Rr
Rr
r
Rr
Rr
There is a 100%
chance (4 / 4) that all
of their children will
be tongue- rollers!
Homozygous or Heterozygous?
What would happen if a tongue roller
had children with a non-tongue roller?
RR
x
r
r
Homozygous
rr
=
?
Homozygous
R
R
Rr
Rr
Rr
Rr
All offspring will
be heterozygous!
But how will the genes be expressed?
10. What is Genotype? = genetic make-up
(alleles)
RR, Rr, rr
11. What is Phenotype = physical characteristics
(expression)
Tongue rollers vs. non-tongue rollers
But how will the genes be expressed?
What is genotype?
Genotype = genetic make-up (alleles)
RR, Rr, rr
What is phenotype?
Phenotype = physical characteristics (expression)
Tongue rollers vs. non-tongue rollers
Practice Problems
If a homozygous dominant parent with dimples had
children with a heterozygous parent with dimples,
what phenotypes could the children have?
D= has dimples, d= no dimples
D
D
d
D
Practice Problems
If a homozygous dominant parent with dimples had
children with a heterozygous parent with dimples,
what phenotypes could the children have?
D= has dimples, d= no dimples
D
D
D
DD
DD
d
Dd
Dd
All offspring will
have dimples!
Practice Problems
If two heterozygous parents with dimples
had children, what phenotypes could the
children have?
D
d
D
d
DD
Dd
Dd
dd
75% chance
offspring will
have dimples!
25% chance
offspring will NOT
have dimples!
Practice Problems
If two heterozygous parents with dimples
had children, what phenotypes could the
children have?
D
D
d
d
Let’s Review:
• What is a GENOTYPE?
• If a girl is heterozygous for eye color, and
the alleles for eye color are brown (B) and
blue (b), what would be her GENOTYPE?
• If a boy has blue eyes and is homozygous
for eye color, what would be his
GENOTYPE?
• Now…what if these two individuals have a
baby?
DOMINANT AND RECESSIVE
TRAITS LAB
“Dominant and Recessive Traits Lab”
Copy and use this chart to survey
people in the class:
YES
Roll Your Tongue
Attached Earlobes
Dimples
Widow’s Peak
Longer Second Toe
Bent Little Finger
Hitchhiker’s Thumb
NO
% with
trait
Dominant VS Recessive
Longer
Second Toe
Shorter
Second Toe
Bent Little
Finger
Straight Little
Finger
Normal
Thumb
Hitchhiker’s
Thumb
Dominant VS Recessive
Tongue
Roller
Can’t Roll
Tongue
Unattached
Earlobes
Attached
Earlobes
Dimples
No Dimples
Widow’s
Peak
No Widow’s
Peak
Extra Slides BelowAdvanced &
Additional material
But how will the genes be expressed?
Genotype
Phenotype
RR
Rr
tongue rollers
rr
non-tongue rollers
*Remember: If a dominant trait is present,
it will always be exhibited.
Mendel’s Laws
Law #2: Law of Segregation
Segregate = to separate
• Alleles segregate during meiosis
T t
T
Meiosis = Copy
DNA once,
Divide twice
T
t
t
4 cells with different alleles
Mendel’s Laws
Law #3: Law of Independent Assortment
Genes for different traits can independently
separate from each other
For example: seed color does not have to
depend on seed shape or vice versa
• Yellow wrinkled seeds and green wrinkled seeds
• Yellow smooth seeds and green smooth seeds
Mendel’s Contributions
The second offspring plants = F2 generation
• The ‘2’ tells you that they are the offspring of
the F1 generation
P generation
1 tall, 1 short
F1 generation
4 tall, no short
F2 generation
3 tall, 1 short
Why Pea Plants?
• They were easy to grow and they grew quickly!
• They had 7 different traits (seed shape, seed color,
pod shape, pod color, height, etc.)
• For each trait, they had 2 distinct forms (yellow vs.
green, short vs. tall)
• They could self-pollinate OR cross-pollinate
Mendel’s Contributions
The original pair of plants = P generation
• P for parental
The first offspring plants = F1 generation
• F for filia (Latin for “daughter”)
P generation
1 tall, 1 short
F1 generation
4 tall, no short
Now it’s time for …
Odd but TRUE!
Burmese Neck Stretching
The Padaung tribe of Burma considered a
long neck beautiful. At age 5, girls were
introduced to the first neck ring. As they
grew, rings were added. Their shoulders
were pushed down, making the neck
look longer.
A fully stretched neck was between 1015" long. A woman could not drink
from a cup, because tipping her head
back would make her fall- she could
only drink from a straw. If a woman
offended her tribe, her rings were cut
off and she would choke to death.
True… but is it a trait?
Families passed the tradition
down. A long neck was a way
to attract good husbands.
Is it possible for a woman
to pass on the trait of a
long neck to her children?
Why or why not?
Write down your thoughts!
Chinese Foot Binding
In the 10th century in China, legend says a
prince began the practice of foot binding
because he loved the small feet of his wife.
A tiny foot became the mark of a wealthy and
well-born woman.
Foot binding began as early as age 4. A
strip of bandage was wrapped tightly around
the foot, and the four small toes were
broken and bent under the sole.
Chinese Foot Binding
The bandage was tightened each day and
the foot was put into smaller and smaller
shoes. An ideal foot was only 4 inches
long. By then, the foot was useless for
walking very far.
Bound feet would bend, becoming so concave they were sometimes
described as "lotus hooks".
True… but is it a trait?
Could a mother whose feet were bound pass on the
trait of small feet to her children? Why or why not?
What are your thoughts?!