 HAPPY THURSDAY 
BELL WORK:
In 33 words, explain how a girl with blue
eyes could have two parents with brown
eyes.
**Turn in your HW – The 2 handouts**
Standard: B6F - Predict possible
outcomes of genetic combinations
such as monohybrid crosses.
Essential Question: How can I
predict genetic outcomes?
Genetics is the
scientific study
of heredity.
Gregor Mendel
is the Austrian
monk who was
particularly
important to
understanding
biological
inheritance.
A trait is a specific characteristic that varies
from one individual to another.
From his experiments,
Mendel concluded that
biological inheritance is
determined by factors that
are passed from one
generation to the next.
The chemical factors that
determine traits are called
genes.
The different forms of a
gene are called alleles.
When mating
two organisms,
the original pair
of organisms is
known as the P
generation.
The “P” in P
generation
stands for
parental.
The offspring of the P generation
is the F1 generation.
“F1” in F1 generation stands for
first filial.
Filius and filia are the Latin words
for son and daughter.
The offspring of crosses between
parents with different traits are
called hybrids.
The principle of
dominance states that
some alleles are
dominant while others
are recessive.
The dominant allele will
always be expressed.
A capital letter is used to
represent a dominant
allele.
When Mendel crossed the F1
generation with itself, one
fourth of the F2 plants showed
the trait controlled by the
recessive allele.
The recessive allele will only be
expressed when the dominant
allele for the trait is not
present.
A lower case letter is used to
represent a recessive allele.
The way in which alleles separate during meiosis does
not follow a pattern. It is completely random.
The results of genetic
crosses can be
explained by the
principles of
probability.
Probability is the
likelihood that a
particular event will
occur.
Probabilities predict the average outcome of a large
number of events.
Probabilities cannot predict the exact outcome of an
individual event.
In probability, sample size eventually determines how close
resulting numbers get to the expected values.
In probability, past
outcomes do not affect
future ones.
The gene combinations that
might result from a genetic
cross can be determined by
drawing a diagram known as a
Punnett square.
The types of gametes produced
by each F1 parent are shown
along the top and left sides of a
Punnett square.
The possible gene
combinations for the F2
offspring appear in the 4 boxes
that make up the square.
The letters in the
Punnett square
represent alleles.
Punnett squares
are used to
predict and
compare the
genetic variations
that will result
from a cross.
Organisms that have two of
the same alleles for a
trait are homozygous
Organisms that have two
different alleles for a
trait are heterozygous.
Homozygous organisms are
true-breeding/purebred
for a trait.
Heterozygous organisms
are hybrid for a trait.
A phenotype is an
organism’s physical
characteristics.
A genotype is an
organism’s genetic
makeup.
Two organisms can
have the same
phenotype but
different
genotypes.
Mendel’s
assumptions
about segregation
predicted a
phenotypic ratio
of 3:1.
Mendel’s
assumptions
about segregation
predicted a
genotypic ratio of
1:2:1.
The fact that genes that
segregate independently
do not influence each
other’s inheritance is
known as independent
assortment.
The principle of
independent assortment
states that genes for
different traits can
segregate independently
during the formation of
gametes.
Independent assortment
helps account for the many
genetic variations
observed in many
organisms.
Punnett Square Steps
1st Step = Identify what letter is being
used
What would be the possible outcomes for the
offspring of a cross between pink flower (PP) and
a white flower (pp)?
“P” and “p”
Punnett Square Steps
2nd Step = Assign the trait for each letter.
What would be the possible outcomes for the offspring of a
cross between pink flower (PP) and a white flower (pp)?
P= PINK
p = WHITE
Punnett Square Steps
3RD Step = Match what letters are being
used for each parent/gender.
What would be the possible outcomes for the
offspring of a cross between pink flower (PP) and a
white flower (pp)?
= PP
DAD
= pp
MOM
Let’s sum it up…..
1st = Identify what letters are being used.
2nd = Assign the trait for each letter.
3rd = Match what letters are being used for each
parent/gender.
4th = Now fill in your Punnett Square.
Punnett Square practice…
1. What would be the possible outcomes for the offspring of a
cross between pink flower (PP) and a white flower (pp)?
p
p
P
P
Pp
Pp
Pp
Pp
P = Pink
p = White
DAD = PP
MOM = pp
**When using the letters like “P and p” OR “C and c”, draw the lowercase letter in
cursive or just make sure you make them look different. Otherwise, you might
confuse the dominant for the recessive **
2. Long fingers are dominant (F) to short fingers (f).
Complete the Punnett square for a homozygous
recessive mom and a heterozygous dominant dad.
f
f
F
f
Ff
ff
F = Long
f = Short
ff
DAD = Ff
MOM = ff
Ff
3. In a plant, long stems are dominant (L) to short stems (l). If a
homozygous dominant flower and a homozygous recessive plant are
crossed, what would be the phenotypic ratio of their offspring?
l
l
L
L
Ll
Ll
L = Long
L = Short
Ll
DAD = LL
MOM = ll
Ll
4. Straight hair (C) is dominant to curly hair (c). What would be
the probability that a child would have curly hair if both
parents are heterozygous dominant?
C
c
C
c
CC
Cc
Cc
cc
C = Straight
c = Curly
DAD = Cc
MOM = Cc
5. Having a hitchhiker's thumb is a dominant trait (T). If
a woman with a straight thumb has a child with a man
who is heterozygous for the trait, what are the chances
their child will have a hitchhiker's thumb?
T
t
t
Tt
tt
t
Tt
tt
T = Hitchhiker
t = Straight
DAD = Tt
MOM = tt
6. What would the phenotypic and genotypic ratios be
for two purple (Pp) flowers that were bred together?
P
p
P
p
PP
Pp
Pp
pp
P = Purple
p = White
DAD = Pp
MOM = Pp
Can you identify your own genotypes
and phenotypes?
Hairline:
Widow’s peak is dominant to
straight hairline
Eye Shape:
Almond eyes
is dominant to round eyes
Eyelash Length:
Long eyelashes is dominant to
short eyelashes
Tongue Rolling:
CAN roll the tongue
is dominant to cannot
Hitchhiker’s Thumb:
Hitchhiker’s thumb is dominant to
straight thumb
Lip Thickness:
Thick lips
are dominant to thin lips