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Human Heredity
Some individuals are able to bend their
thumb back at the distal joint at 50° or more
PTC Taster
• The ability to detect a specific taste from
the chemical phenylthiocarbamide (PTC)
has been labeled as the trait PTC Tasting
or Taster..
• The gene for this trait has been mapped to
the long arm of chromosome 7.
Individual Phenotypes
Thumb
Bent
Straight
Tongue Roll
Roller
Non-roller
Little Finger
Bent
Straight
Earlobes
Free
Attached
PTC
Taster
non
Class Phenotypes
Thumb
Bent
# of
students
% of
students
Straight
Tongue Roll
Roller
Nonroller
Little Finger
Bent
Earlobes
Straight Free
Attache
d
PTC
Taster
non
How do the class data compare to
the actual answers?
Bent
Pinky Straight
Dominant
Roller
Non-roller
Dominant
Thumb Bent
Straight
Dominant
Free
Attached
Dominant
Taster
non
Dominant
Heredity
DNAdeoxyribonucleic
acid, stores genetic
information
NOVA Online | Cracking the Code of Life |
Gene- a segment of
DNA that codes for
a trait
9 min, 6 min
Heredity
ChromosomeChromatinrod-shaped body,
loosely stored,
found in the
relaxed DNA
nucleus, made of
25 to 30 THOUSAND
the DNA molecule
genes at “rest”
Mendel’s “factors”
Are Chromosomes!
video clip
Karyotyping
• In your lab tutorial, you looked at three
patients who needed diagnosis.
For all three patients, what was the trouble?
• Specifically A? B? C?
Last name lineup, check in Lab Notes
Genetics- field of biology, study of
heredity
Heredity- how characteristics are
passed from parent to offspring
These black Labrador
puppies are purebred—their
parents and grandparents
were black Labs
with very similar genetic
makeups.
• The parents of these puppies were a
mixture of different breeds
– Their behavior
and
appearance is
more varied as
a result of their
diverse genetic
inheritance
Gregor Mendel
FLOWER
COLOR
Purple
White
Axial
Terminal
SEED
COLOR
Yellow
Green
SEED
SHAPE
Round
Wrinkled
POD
SHAPE
Inflated
Constricted
POD
COLOR
Green
Yellow
STEM
LENGTH
Tall
Figure
9.2A, B
Dwarf
• WHO WAS HE?
– Father of Genetics
– Monk who lived in mid-1800s
– worked with pea plants and
researched heredity
Mendel observed
7 different plants
characteristics of
peas. These
characteristics
were called
traits…
FLOWER
POSITION
G. Mendel
FLOWER
COLOR
Purple
White
Axial
Terminal
SEED
COLOR
Yellow
Green
SEED
SHAPE
Round
Wrinkled
POD
SHAPE
Inflated
Constricted
POD
COLOR
Green
Yellow
STEM
LENGTH
Tall
Figure
9.2A, B
Dwarf
FLOWER
POSITION
• Three Key CHOICES– Control over the breedings
– Use of purebred plants for
Parent Gen.
– Written observations of “eitheror” traits
Mendel Cont.
• Peas are great to study
because
– Only two possible
characteristics per trait
– they easily cross-pollinate
– and have many offspring!
• Trait- a category that has
two or more contrasting
characteristics
– Ex- seed color
What are each of the traits
shown in the pairs below?
Flower
Color
Flower
Position
Seed
Color
Seed
Shape
Pod
Shape
Pod
Color
Stem
Length
Mendel’s Experiments
• In Mendel’s plant
experiments, he used
special names to
describe each generation
of pea plants
• P1 generation- parent
generation
• F1 generation- offspring
of parent generation
• F2 generation- offspring
of F1 generation
Mendel and his Experiments- Video
White
RESULTS
Dominant- (capital)
a trait that covers
another
1
Removed
stamens
from purple
flower
Stamens
Carpel
PARENTS
(P)
2 Transferred
Purple
pollen from
stamens of white
flower to carpel
of purple flower
3 Pollinated carpel
matured into pod
Recessive- (lowercase letter) trait that
is hidden by a
dominant gene
4
OFFSPRING
(F1)
Planted
seeds
from pod
Survey 5 people (including yourself)
Based on your data,
is a Widow’s peak dominant or recessive?
What is your genotype?
(Hint: assign letters for Widow’s peak and no Widow’s peak)
Alleles
• different forms of a gene that code for a trait
• reside at the same place on homologous
chromosomes
Example- Bb
GENE
P
P= purple
p = white
A = axial
a= terminal
B= buds
b= no buds
P
a
a
B
DOMINANT
allele
b
RECESSIVE
allele
GENOTYPE:
PP
aa
HOMOZYGOUS
for the
dominant allele
HOMOZYGOUS
for the
recessive allele
Mendel’s Laws, Genotype vs. Phenotype- Video
Bb
HETEROZYGOUS
Figure 9.4
Genotype- genetic makeup of an organism
(alleles)
Example- PP
Phenotype – physical appearance of an organism
Example- purple colored petals
gene
P
a
B
P= purple
p = white
A = axial
a= terminal
P
a
b
RECESSIVE
allele
B= buds
b= no buds
GENOTYPE:
PP
aa
HOMOZYGOUS
for the
dominant allele
HOMOZYGOUS
for the
recessive allele
Bb
HETEROZYGOUS
Figure 9.4
For those with
a widow’s
Why is your
genotype W?
Homozygous= Purebred = having two copies of
the same allele; BB or bb
Heterozygous= Hybrid = two different alleles; Bb
gene
P
a
B
P= purple
p = white
A = axial
a= terminal
P
a
b
RECESSIVE
allele
B= buds
b= no buds
GENOTYPE:
PP
aa
HOMOZYGOUS
for the
dominant allele
HOMOZYGOUS
for the
recessive allele
Bb
HETEROZYGOUS
Figure 9.4
Review Question
What is the difference between genes and
alleles?
Example: Blood type is the gene, what
would the alleles be?
Pg.205
Hair
length
Short L Long l
Hair
texture
Hair
curliness
Wiry T
Should this Dog
be named Spot?
Silky t
Curly H Straight h
Coat
Spot A Solid a
pattern
What is his GENOtype?
L
t
l
T
H
A
What is his PHENOtype?
What trait is he Homozygous for?
H a
Mendel: Law of Segregation
From his pea experiments,
Mendel believed:
• Each individual inherits 2
copies of every gene.
• During the formation of
gametes, the 2 copies of
a gene separate
“segregate” (1 copy in
every gamete).
Parent 1
What happens when the F1s cross?
Parent 2
Law of Segregation Cont.
MONOHYBRID CROSSES
• Monohybrid Cross- involves
one pair of contrasting traits
– Example- Cross a male
and female, determine the
gender of offspring
• Punnett SquareWho? R.C.Punnett, geneticist
What? tool used to predict the
outcomes of crosses
Punnett squares Who? P.183
• The Punnett square: grid system for predicting
all possible genotypes from a mating (cross).
– axis- each parent
possible gametes
– inside grid possible
offspring genotypes
• Punnett square yields
ratio of potential
genotypes and
phenotypes.
Law of Independent AssortmentFactors for different
characteristics are
distributed to
gametes
independently
A dihybrid cross involves two traits.
• Mendel’s dihybrid crosses led to his second law,
the law of independent assortment.
• The law of independent
assortment states that
allele pairs separate
independently of each
other during meiosis.
• Mendel’s dihybrid
crosses with
heterozygous plants
yielded a 9:3:3:1
phenotypic ratio.
Dragon Lab
Mom
Dad
Alleles in
Egg
Alleles
in
Sperm
Baby
Phenotype
Genetics and Probability
• Probability- the likelihood that a specific
outcome will occur
– Expressed as: a fraction, decimal ratio, or %
– In a basic Punnett Square, you have four 4
boxes so your ratios could be
1:4 (25%) , 2:4(50%) , 3:4(75%) , 4:4 (100%)
Mendel’s works :
126 red: 122 white
126/248 = 50.8 % P(red)
Your Notes look like this…
EACH
WILL
BE A
SEPARATE
EXAMPLE
Punnett
Squares
Example 1:
Homozygous x Homozygous
Homozygous for purple PP = purple
Genotypic Ratio:
Homozygous for white pp = white
Phenotypic Ratio:
Example 2:
Homozygous x Heterozygous
Homozygous for black coat BB
Genotypic Ratio:
Heterozygous for black coat Bb
Phenotypic Ratio:
Example 3:
Heterozygous x Heterozygous
Heterozygous for black coat Bb Heterozygous for black coat Bb
Genotypic Ratio:
Phenotypic Ratio:
Example 4: Testcrossindividual of unknown genotype is crossed
with a homozygous recessive individual
UNKNOWN!
Is he BB or Bb?
Genotypic Ratio:
Homozygous
Recessive
Phenotypic Ratio:
TEST CROSS
Results tell whether tested
individual is PUREBRED or
HYBRID dominant.
---Test Cross Ex. Would give 100%
Dominant offspring if the individual
was PURE for the dominant trait.
---ANY recessive phenotype
offspring mean the tested
parent must have been
HETEROZYGOUS
Test Cross example 2
P1 -
F1 -
?Unknown Dominant?
ROUND
? RR -or- Rr ?
X
Homozygous Recessive
wrinkle
We know is [[ rr ]]
If offspring are ALL round,
then unknown parent was ______________
If some offspring phenotype shows wrinkles,
then the unknown parent was ___________
Smiley :
Genotype vs. Phenotype
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» List Hour #
CROSS
OFFSPRING
Long stem x long
stem
787 long
277 short
Green pods x green
pods
428 green 152
yellow
ACTUAL
RATIO
APPROXIMATE
RATIO
CROSS
OFFSPRING
Peas with axial
flowers x peas
with terminal
flowers
652 axial
flowers
206 terminal
flowers
Fruit flies, normal
wings x curly
wings
103 normal
wings
92 curly
Oval radishes x
oval radishes
25 long radishes
52 oval radishes
28 round
radishes
Tongue rollers x
tongue rollers
755 tongue
rollers
245 non-rollers
ACTUAL
RATIO
APPROXIMATE
RATIO
Beyond Mendel
More Complex Inheritance
& Sex-Linked Traits
Incomplete Dominance
• An inheritance
relationship in which a
“mix” or blend of the
two alleles is
produced
Incomplete Dominance
• A cross between round radishes and long
radishes produces oval radishes.
(incomplete dominance).
A cross between round radishes and long
radishes produces oval radishes. (incomplete
dominance). If oval radishes were selling for
the most money, what would you cross for
highest profit?
a. round x round
c. oval x oval
b. round x long
d. long x oval
Co-Dominance
-Both alleles are visible in
the phenotype
-examples- Lubber
grasshopper or a roan
horse--- or my sable corgi !
The lubber grasshopper is a
very large grasshopper, and
is black with red and yellow
stripes.
A. What is the expected
1 RW: 0
genotypic ratio of the F1
generation?
B. What is the expected
phenotypic ratio of the F1
1 roan: 0
generation?
C. What percent is expected to
be white?
0%
D. How do incomplete dominance
and co-dominance differ?
E. Using your text, explain how
blood typing illustrates both
complete dominance and codominance?
Example 1: Homozygous x
Homozygous
Round (RR) Yellow (YY) seeds crossed with Wrinkled (rr) green (yy) seeds
Genotypic Ratio:
Phenotypic Ratio:
Dihybrid Cross
• Mono = One… so Monohybrid cross we
were only focusing on ONE trait.
• Di = Bi = Two
So DiHybrid
cross
considers
two traits at
the same
time.
Example 1
X
Dihybrid Cross pg. 171
Round= R wrinkle= r // Yellow = Y green=y
RY
RY
Ry
rY
ry
Ry
rY
ry
Example 2: Heterozygous x
Heterozygous
Round (Rr) Yellow (Yy) seeds crossed with Round (Rr) Yellow (Yy) seeds
Genotypic Ratio:
Phenotypic Ratio:
Dihybrid cross GgNn x GgNn
GN
Gn
gN
gn
GN
GGNN GGNn GgNN
GgNn
Gn
GGNn GGnn
GgNn
Ggnn
gN
GgNN
GgNn
ggNN
ggNn
gn
GgNn
Ggnn
ggNn
ggnn
Phenotypic ratio:
9 green, smooth:
3 green, wrinkled
3 yellow smooth
1 yellow wrinkled
REVIEW Genetic Crosses
homozygous = having two copies of the same
allele
heterozygous = having two different alleles
Genotype- genetic makeup of an organism
(alleles)
Phenotype – physical appearance of an organism
1. Guinea pigs
1. Black -
white –
3. Punnett square –
4. Genotypic ratio:
5. Phenotypic ratio:
2. ____ x ____
2. Curly vs Straight
C= curly
c = straight
Cc x cc
genotypic ratio: 1 Cc : 1 cc
phenotypic ratio : 1 curly: 1 straight
C
c
c
c
Cc
Cc
cc
cc
3. In peas. . .
1. Tall -
dwarf –
3. Punnett square –
4. Genotypic ratio:
5. Phenotypic ratio:
2. ____ x ____
The following
traits are
dominant:
+brown eyes
+curly hair
+attached
earlobes
+curling tongue.
Which one is
Wanda’s mom?
Dad =
Brown B?
curly C?
unattached aa
roller R?
Wanda=
Brown B?
curly C?
attached A?
roller R?
MOM 1
Wanda got a from dad, had to get
the A from mom, Mom one has a
A to give
The following traits are
dominant:
brown eyes
curly hair
attached earlobes
rolling tongue
Probability of 2 coins
Coin #1
H
H
T
T
Coin #2
H
T
H
T
1/4
¼ + ¼ = ½ OR
1/4
H
T
H
HH
HT
T
HT
TT
Test cross- an unknown genotype is crossed
with a homozygous recessive individual
TESTCROSS:
B_?
GENOTYPES
bb
Two possibilities for the black dog:
BB
Bb
B
GAMETES
b
OFFSPRING
or
Bb
All black
B
b
Bb
b
bb
1 black : 1 chocolate
6. In mice, black coat is dominant over white.
Outline possible crosses to determine whether
a black mouse is homozygous or
heterozygous.
___ = black
___ = white
_______ x _bb___
(black)
(testcross)
BB or Bb
Pg 10 #7
If two black mice are mated several times. . .
Results:
23 black : 8 white
What do you know about the parents?
Lubber Grasshopper (co-dominant)
The lubber grasshopper
is a very large
grasshopper, and is
black with red and
yellow stripes.
RR = red stripes
YY = yellow stripes
RY = red and yellow
stripes
4. Cross two lubbers,
both with red and yellow
stripes. List phenotypic
ratio. 1 red: 2 red and yellow: 1 yellow
Running mice =
Waltzing mice =
Black =
brown =
1.
hom. run/hom.black x
hetero run/hetero blk
________ x ________
In mice. . .
RB
RB
Rb
RRBB
RRBb
rB
RrBB
Phenotypic ratio:
rb
RrBb
2. ___________ x _____________
hetero run
hetero black
Answer:
hetero run
pure brown
3 run black:
1 waltz black:
3 run brown:
1 waltz brown
Answers to dihybrid practice
problems
1. Phenotypic ratio: 4 run black :0
2. Phenotypic ratio:
3 run black
1 waltz black:
3 run brown:
1 waltz brown
3. Phenotypic ratio: 1 run black: 1 run brown
4. Phenotypic ratio: 3 run black: 1 waltz black
Genetic corn
What phenotypes do you see on your cob?
Brown & Smooth (A),
Brown & wrinkled (B),
Yellow & Smooth (C)
Yellow & Wrinkled (D).
Which is dominant?
Brown =
Yellow =
Smooth =
wrinkled =
If the P1 generation was heterozygous for both traits, hypothesize
what will be your phenotypic ratio?
Phenotypes
Description
Number present
Class Results
Ratios
1
2
3
brown
brown
yellow
smooth
llll
wrinkled smooth
ll
ll
4
yellow
wrinkled
l
brown
smooth
Class Results
Brown
Yellow
smooth
wrinkled
Yellow
wrinkled
Corn Punnett Square
BS
BS
Bs
bS
bs
Phenotypic ratio:
9 brown, smooth:
3 brown, wrinkled
3 yellow, smooth
1 yellow, wrinkled
Bs
bS
bs
Dihybrid Lab
• In corn, brown kernels are dominant over
yellow kernels.
• Smooth texture is dominant over wrinkled.
• Cross a hybrid brown, wrinkled corn with a
yellow, heterozygous smooth corn.
• What percent will be brown and smooth?
Pg 22 # 5 Aliens from Mars
_______________ x _______________
hetero for both
hetero for both
1. E= 2 eyes
e = 1 eye
T = triangle
t = pentagon
Aliens from
Mars
2. EeTt x EeTt
A. What is the expected genotypic ratio
of the F1 generation?
1 RW: 0
B. What is the expected phenotypic
ratio of the F1 generation?
1 pink: 0
C. What percent is expected to be
white?
D. If for Valentine’s Day a florist wanted0%
all pink flowers, what would be the
phenotypes for the parents?
Red x white
Genetic Word Problems
1. Red is INCOMPLETELY dominant over
white
RW
WW
Red =
________ x ________
RR
White = WW
pink
white
R
W
RW
Pink =
W
RW
WW
W
RW
WW
Genetic Word Problems
2.
Red =
White =
roan =
________ x ________
roan
roan
1. Genotype ratio: 1RW : 1WW
Phenotype ratio: 1 pink: 1 white
2. Genotypic ratio
Phenotypic ratio
% dominant
1 RR: 2 RW: 1WW
1 red : 2 roan: 1 white
50%
3.
1 AA: 1Aa
1 dominant: 0
100%
Genotypic ratio
Phenotypic ratio
% dominant
4. Genotypic ratio
Phenotypic ratio
% dominant
1 YyWw: 1 Yyww
1 yellow web: 1 yellow hoof
yes 50%