Genetics
Genetics: what is it?
What is the study of genetics?
◦ “Genetics is the study of heredity, the process in which a
parent passes certain genes onto their children.”
What does that mean?
◦ Children inherit their biological parents’ genes that express
specific traits, such as some physical characteristics, natural
talents, and genetic disorders.
2
Word Match Activity
Match the genetic terms to their
corresponding parts of the illustration.
•base pair
•cell
•chromosome
•DNA
(Deoxyribonucleic Acid)
•genes
•nucleus
3
nucleus
Word Match Activity
•base pair
chromosome
cell
•cell
•chromosome
•DNA
(Deoxyribonucleic Acid)
•genes
•nucleus
base
pair
(double
helix)
DNA
genes
4
The History of Genetics
Genetics is the study of genes.
Inheritance is how traits, or characteristics, are passed
on from generation to generation.
Chromosomes are made up of genes, which are made up
of DNA.
Genetic material (genes,chromosomes, DNA) is found
inside the nucleus of a cell.
Gregor Mendel is considered “The Father of Genetics"
Gregor Johann Mendel
Austrian monk Called the “Father of Genetics"
Studied the inheritance of traits in pea plants
Developed the laws of inheritance.
Mendel's work was not recognized until the turn of the 20th century
Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea
plants
He found that the plants' offspring retained traits of the parents
6
Site of Gregor
Mendel’s
experimental
garden in the
Czech Republic
7
What did he
actually do to the
plants?
Mendelian Genetics
Dominant traits- traits that are expressed. Genotype- the types of genes
(Alleles) present.
Recessive traits- traits that are covered
up.
Phenotype- what it looks like.
Alleles- the different forms of a
characteristic.
Homozygous- two of the same
alleles.
Punnett Squares- show how crosses are
made.
Heterozygous- two different
alleles.
Probability- the chances/ percentages
that something will occur.
GENOTYPE
PHENOTYPE
the types of genes (Alleles)
present
what it looks like
Mendel’ Pea Plants
Mendel based his laws on his studies of garden
pea plants. Mendel was able to observe
differences in multiple traits over many
generations because pea plants reproduce
rapidly, and have many visible traits such as:
Pod color
Green
Yellow
Seed Shape
Plant Height
Tall
Short
Seed Color
Green
Yellow
Pod Shape
Smooth Pinched
Wrinkled
Round
Mendel’s Experiments
Mendel noticed that some plants always produced offspring that had a form of
a trait exactly like the parent plant. He called these plants “purebred” plants.
For instance, purebred short plants always produced short offspring and
purebred tall plants always produced tall offspring.
X
Purebred Short Parents
Short Offspring
X
Purebred Tall Parents
Tall Offspring
Mendel’s First Experiment
Mendel crossed purebred plants with opposite forms of a trait. He called these plants the
parental generation , or P generation. For instance, purebred tall plants were crossed with
purebred short plants.
X
Parent Tall
P generation
Parent Short
P generation
Offspring Tall
F1 generation
Mendel observed that all of the offspring grew to be tall plants. None
resembled the short short parent. He called this generation of offspring the
first filial , or F1 generation, (The word filial means “son” in Latin.)
Mendel’s Second Experiment
Mendel then crossed two of the offspring tall plants produced from his first
experiment.
Parent Plants
Offspring
X
Tall
F1 generation
3⁄4 Tall & 1⁄4 Short
F2 generation
Mendel called this second generation of plants the second filial, F2,
generation. To his surprise, Mendel observed that this generation had a mix
of tall and short plants. This occurred even though none of the F1 parents
were short.
Mendel’s Law of Segregation
1. Plant traits are handed down through “hereditary factors” in the sperm
and egg.
2. Because offspring obtain hereditary factors from both parents, each plant
must contain two factors for every trait.
3. The factors in a pair segregate (separate) during the formation of sex
cells, and each sperm or egg receives only one member of the pair.
Dominant and Recessive Genes
One factor (gene) in a pair may mask, or hide, the other factor.
• For instance, in his first experiment, when he crossed a purebred tall plant
with a purebred short plant, all offspring were tall. Although the F1
offspring all had both tall and short factors, they only displayed the tall
factor. He concluded that the tallness factor masked the shortness factor.
• Today, scientists refer to the “factors” that control traits as genes. The
different forms of a gene are called alleles.
• Alleles that mask or hide other alleles, such as the “tall” allele, are said to
be dominant.
• A recessive allele, such as the short allele, is masked, or covered up,
whenever the dominant allele is present.
Homozygous Genes
What Mendel referred to as a “purebred” plant we now know this to mean
that the plant has two identical genes for a particular trait. For instance, a
purebred tall plant has two tall genes and a purebred short plant has two
short genes. The modern scientific term for “purebred” is homozygous.
short-short
short-short
short-short
X
Short Parents
Short Offspring
Law of Segregation each parent donates one height gene to the offspring.
Since each parent had only short genes to donate, all offspring will also have
two short genes (homozygous) and will therefore be short.
Hybrid (Heterozygous) Alleles
In Mendel’s first experiment, F1 offspring plants received one tall gene and
one short gene from the parent plants. Therefore, all offspring contained both
alleles, a short allele and a tall allele. When both alleles for a trait are
present, the plant is said to be a hybrid for that trait. Today, we call hybrid
alleles heterozygous.
short-tall
short-tall
tall-tall
short-short
X
Parent Short
P generation
Parent Tall
P generation
Offspring Tall
F1 generation
Offspring have both a tall and a short allele, only the tall allele is expressed
and is therefore dominant over short.
Dominant and Recessive Genes… The Law of
Dominance
• Gene that prevents the other gene from “showing” –
dominant (there are a few exceptions to this …)
• Gene that does NOT “show” even though it is present –
recessive
• Symbol – Dominant gene – upper case letter – T
Recessive gene – lower case letter – t
Dominant
color
Recessive
color
Dominant vs Recessive Alleles
Mendel observed a variety of dominant alleles in pea plants other than the tal
allele. For instance, hybrid plants for seed color always have yellow seeds.
Green & Yellow Allele
Yellow Seed
However, a plant that is a hybrid for pod color always displays the green
allele.
Green Pod
Green & Yellow Allele
Round seeds are dominant over wrinkled seeds, and smooth pods are
dominant over wrinkled pods.
• Chromosomes come in homologous pairs, thus genes
come in pairs.
Homologous pairs – matching genes – one from female
parent and one from male parent
• Example: Humans have 46 chromosomes or 23 pairs.
One set from dad – 23 in sperm
One set from mom – 23 in egg
Alleles – different genes (possibilities) for
the same trait
ex: purple or white flowers
To be purebred or not to be purebred
that is the question…
An organism that always produces an offspring with
the same physical / genetic characteristic(s).
1. P Generation – Parents
2. F1 Generation – Offspring from parents
3. F2 Generation – Offspring from F1
Law of Segregation
Each gamete only donates one allele for each gene.
Law of Independent Assortment: each pair of genes
separate independently of each other in the production of sex cells.
• Gene pairs will separate during the formation of egg or sperm
cells.
• Plant will donate one allele from each pair
• Plant will donate either a yellow or green seed allele, either a
yellow or green pod allele, and a wrinkled or round seed allele
•
Plant will always donate a wrinkled pod shape
• The donation of one allele from each pair is independent of any
other pair.
• Ex: if the plant donates the yellow seed allele it does not mean
that it will also donate the yellow pod allele.
Example: Straight thumb is dominant to hitchhiker thumb
T = straight thumb t = hitchhikers thumb
(Always use the same letter for the same alleles—
No S = straight, h = hitchhiker’s)
Straight thumb = TT
Straight thumb = Tt
Hitchhikers thumb = tt
* Must have 2 recessive alleles
for a recessive trait to “show”
The Punnett Square
Probability
- The likelihood an event will or will not occur.
Ex. What is the probability of flipping heads?
50 -- 50 , ½, 50%
Ex. What is the probability of pulling an ace out of a deck of
cards?
4 -- 52 , 1/13, 7.7%
The prior occurrences have no effect on future results – it is all
chance and it starts over each time.
Punnett Squares
The Punnett square is the
standard way of working out what
the possible offspring of two
parents will be.
◦It is a helpful tool to show allelic
combinations and predict
offspring ratios.
Types of Genetic Crosses
Monohybrid cross - cross involving a
single trait (We will cover these first.)
e.g. flower color
Dihybrid cross - cross involving two traits
e.g. flower color & plant height
32
How to set up a Punnett Square…
Begin by constructing a grid of two perpendicular lines.
How to set up a Punnett Square…
One parents traits go on
top 
For this example lets consider a genotype
of BB crossed with bb.
B
b
b
B
• Notice only one
letter goes above each
box
• It does not matter
which parent’s
genotype goes on
either side.
Next, fill in the boxes by copying the column and
row head-letters down and across into the empty
spaces. Notice how the capitol letter is always first.
B
B
b
Bb
Bb
b
Bb
Bb
Punnett Squares
Now that we have learned the basics
of genetics lets walk through some
examples using Punnett Squares.
W
w
Usually write the capital
letter first
W WW Ww
Lets say:
w Ww
w- recessive violet
ww
W- dominant white
heterozygous (Ww).
Parents in this cross are __________________________
Note: Make sure I can tell your capital letters from lowercase
letters.
What percentage of the offspring will have violet flowers?
ANSWER: 25% (homozygous recessive)
_____________________________________________
Red hair (R) is dominant over blond hair (r). Make a cross
between a heterozygous red head and a blond.
R
r
r
r
Rr
rr
Rr
rr
What percentage of the offspring will have red hair?
50%
Black eyes (E) is dominant over red eyes (e)
in rats. Make a cross between a homozygous rat with
black eyes and a rat with red eyes.
e
e
E
Ee
Ee
E
Ee
Ee
What is the possibility
of a red eye off
springs?
0% Which is
good because
red eyes are
creepy…
THE DIHYBRID CROSS
STUDYING THE INHERITANCE OF TWO CHARACTERS
SIMULTANEOUSLY
Mendel’s peas
Character
Trait
Allele
Seed shape
Round
R
Wrinkled
Yellow
r
Y
Green
y
Pea color
Combinations
Genotype
Phenotype
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy
Round Yellow
Round Yellow
Round Yellow
Round Yellow
Round Green
Round Green
Wrinkled Yellow
Wrinkled Yellow
Wrinkled Green
Is the inheritance of one character affected by the
inheritance of another?
P Phenotypes
Round
Yellow
F1 Phenotypes
x
Wrinkled
Green
All Round
Yellow
(Pure Bred)
(Selfed)
F2 Phenotypes
Seed color
Yellow
Green
TOTAL
Seed
Round
315
108
423
shape
Wrinkled
101
32
133
TOTAL
416
140
556
RATIO
RATIO
Is the inheritance of one character affected by the
inheritance of another?
P Phenotypes
Round
Yellow
F1 Phenotypes
x
Wrinkled
Green
All Round
Yellow
(Pure Bred)
(Selfed)
F2 Phenotypes
Seed color
Yellow
Green
TOTAL
RATIO
Seed
Round
315
108
423
3.18
shape
Wrinkled
101
32
133
1
TOTAL
416
140
556
RATIO
2.97
1
A dihybrid cross can be treated as two separate monohybrid crosses.
The expected probability of each type of seed can be calculated:
How would you do this?
Probability of an F2 seed being round =
Probability of an F2 seed being wrinkled =
Probability of an F2 seed being yellow =
Probability of an F2 seed being green =
A dihybrid cross can be treated as two separate monohybrid crosses.
The expected probability of each type of seed can be calculated:
How would you do this?
R
R
r
r
A dihybrid cross can be treated as two separate monohybrid crosses.
The expected probability of each type of seed can be calculated:
How would you do this?
R
r
R
RR
Rr
r
Rr
rr
A dihybrid cross can be treated as two separate monohybrid crosses.
The expected probability of each type of seed can be calculated:
How would you do this?
Probability of an F2 seed being round =75% or ¾
Probability of an F2 seed being wrinkled =
Probability of an F2 seed being yellow =
Probability of an F2 seed being green =
A dihybrid cross can be treated as two separate monohybrid crosses
The expected probability of each type
of seed can be calculated:




Probability of an F2 seed being round = 75% or ¾
Probability of an F2 seed being wrinkled = 25% or ¼
Probability of an F2 seed being yellow = 75% or ¾
Probability of an F2 seed being green = 25% or ¼
Or together…Therefore

Probability of an F2 seed being round and yellow
= ¾ x ¾ = 9/16 =
56.25%

Probability of an F2 seed being round and green
=

Probability of an F2 seed being wrinkled and yellow
=

Probability of an F2 seed being wrinkled and green
=
Therefore
Probability of an F2 seed being round and yellow
= ¾ x ¾ = 9/16 =
56.25%
Probability of an F2 seed being round and green
= ¾ x ¼ = 3/16 =
18.75%
Probability of an F2 seed being wrinkled and yellow
= ¼ x ¾ = 3/16 =
18.75%
Probability of an F2 seed being wrinkled and green
=¼x¼=
1/16 =
6.25%
Predicting how many seeds we could expect to
get in a sample
556 x 9/16 round yellow
We could
expect
What Mendel
observed
313
315
556 x 3/16 round green
108
556 x 3/16 wrinkled yellow
101
556 x 1/16 wrinkled green
32
Predicting how many seeds we could expect to get in a sample
We could What Mendel
expect
observed
556 x 9/16 round yellow
313
315
556 x 3/16 round green
104
108
556 x 3/16 wrinkled yellow
104
101
556 x 1/16 wrinkled green
35
32
REMEMBER  THE LAW OF INDEPENDENT
ASSORTMENT
It appears that the inheritance of seed shape has no influence
over the inheritance of seed colour
The two characters are inherited INDEPENDENTLY
The pairs of alleles that control these two characters assort
themselves independently
Mendel & Meiosis: The pairs of chromosomes
could orientate in different ways at Anaphase 1
Dihybrid cross genetic diagram
P
Phenotypes Round Yellow
seed
Genotypes
Gametes
X
Wrinkled
Green seed
RRYY
rryy
meiosis
meiosis
RY
ry
(Pure bred)
fertilisation
F1 Phenotypes
RrYy
Genotypes
Round Yellow
Proportions
100%
(Selfed)
Dihybrid cross genetic diagram
F1 Phenotypes
RrYy
Genotypes
Round Yellow
Proportions
100%
(Selfed)
meiosis
Gametes
Y
y
R
RY
Ry
r
rY
ry
Dihybrid cross genetic diagram
Gametes
Y
y
R
RY
Ry
r
rY
ry
fertilisation
F2
Genotypes
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
Dihybrid cross proportions
Phenotypes
Round Yellow
Round Green
Wrinkled Yellow
Wrinkled Green
Proportions
9/16 or 56.25%
Dihybrid cross proportions
Phenotypes
Round Yellow
Proportions
9/16 or 56.25%
Round Green
3/16 or 18.75%
Wrinkled Yellow
3/16 or 18.75%
Wrinkled Green
1/16 or 6.25%
Dihybrid test cross
In monohybrid crosses, to know if a dominant trait is
homozygous (RR) or heterozygous (Rr) it is necessary to
carry out a test cross.
This is done with a homozygous recessive (rr) individual
The same is true for a dihybrid cross where the test
cross is made with an individual which is homozygous
recessive for both characters (rryy).
Dihybrid test cross
Phenotypes
Genotypes
Round Yellow
RrYy
Gametes
RY, Ry, rY, ry
Genotypes
ry
Phenotypes
X
Wrinkled Green
rryy
ry
RY
Ry
rY
ry
RrYy
Rryy
rrYy
rryy
Round
Round
Wrinkled
Wrinkled
Yellow
Green
Yellow
Green
Proportions 1/4 or 25% 1/4 or 25% 1/4 or 25% 1/4 or 25%
Dihybrid Crosses Use the FOIL method!
- To get the proper segregation of alleles for the parents in a dihybrid cross,
use the FOIL method:
First, Outer, Inner, Last
(Bb)(Tt)
BT, Bt, bT, bt
- There are a lot of genotypes, we only record the phenotypic ratio like this:
Dom, Dom: Dom, Rec: Rec, Dom: Rec, Rec
9:
3:
3:
1
(It needs to add to 16!)
So Remember…. Dihybrid Crosses are:
- A cross involving two traits.
- Create a table with 4 columns & 4 rows.
Example 1:
Black hair is dominant to blonde hair. Being tall is dominant to
being short. What would be the possible phenotypes of a cross
between a heterozygous black-haired, tall female with a male
who is homozygous for having black hair and being short?
Parent Genotypes?
Now you try some…
ON THE REVIEW WORKSHEETS…
Sometimes the laws are
violated…
What we already know about Dominant/Recessive
One allele is dominant over the other (capable of masking
the recessive allele)
PP = purple
pp = white
Pp = purple
What we already know about Dominant/Recessive
In pea plants, purple flowers (P) are dominant
over white flowers (p) show the cross between
P
p
two heterozygous plants.
GENOTYPES:
PHENOTYPES:
P
p
Are there always dominants and recessives?
Not all traits are purely dominant or purely recessive. Can you
think of one that we discussed being this way?
In some cases, neither are dominant.
Incomplete
dominance
When this happens it is known as ________________________
So what do you think?
If neither trait is dominant, what do you think
happens?
◦Do they both show?
◦Neither?
◦A Mixture?
Well, in actuality, there is a ________
mixture of traits
Blending of the Traits
The blending gives intermediate expression
What is intermediate expression?
◦ New phenotypes that are shown when incomplete
dominance of genes occurs
What sorts of genotype is needed for this?
Heterozygous individuals. Why?
◦Only happens in ____________
Why only in heterozygotes
We know that homozygous individuals have the same
allele for both trait (BB or bb).
Heterozygous individuals have _________
different alleles for
both traits and therefore both of the traits ______
show in
New traits
expression levels producing some _______
Incomplete Dominance
A third (new) phenotype appears in the heterozygous
condition ONLY!!!
CRCR = red
CwCw = white
CRCw = pink
Example Cross
w
C
R
C
R
C
w
C
CR CR
C R Cw
CR Cw
Cw Cw
Real Life Examples
Roses
Carnations
Snapdragons
Problem: Incomplete Dominance
Show the cross between a pink and a white flower.
GENOTYPES/ PHENOTYPES
w
C
w
C
CR
CR Cw
CR Cw
Cw
Cw Cw
Cw Cw
Why does it happen?
w
R
R
* Individuals with a single C (ie., C C )
allele are unable to make enough red
pigment to produce the red flowers
* Individuals that are white produce no
red pigment
* So the resulting flowers are pink.
What have we seen?
We have seen now that some alleles can be
dominant, others recessive, and some are not,
dominance
and we call these Incomplete
_________________
Are there any other combinations of alleles that
we may be interested in looking at?
What about this…
Is there a possibility that two alleles for the same trait
can both be dominant?
◦___________________
Co-dominance
But what does this mean for expression?
◦Are the individuals going to take one over another
◦Neither?
◦Both?
Expression
When we have two alleles that are both
dominant we actually get expression of both
We will use the example of chickens
◦Some chickens are black
◦Some chickens are white
Expression
Examples
What about in Humans?
Co-dominance in Humans
The heterozygous condition, both alleles are expressed
AHbS
Hb
____________________
Sickle Cell Anemia in Humans
HbAHbA =
HbSHbS=
HbAHbS =
normal cells
sickle cells
some of each
Human Example –
Electron Micrograph
•Individuals with HbAHbS are also
called carriers
•This means that they carry the
gene for sickle cell anemia, but it is
not expressed to its fullest extent
Think Back
Could changes in an individual be good for an individual in some
cases?
◦ Yes! Of course they could
What is an advantage of having sickle cell anemia?
Harder to get Malaria
◦ _____________________________________
Problem: Co-dominance
Show the cross between an individual with
sickle-cell anemia and another who is a carrier
but not sick.
GENOTYPES/ PHENOTYPES:
Problem: Co-dominance
Show the cross between an individual with
sickle-cell anemia and another who is a carrier
but not sick.
HbS
HbS
HbS
HbS HbS
HbS HbS
HbS HbA
HbS HbA
GENOTYPES/ PHENOTYPES:
A
Hb
Another Tally
So far we have looked at dominance, recessiveness,
Incomplete dominance and Co-Dominance
But what do all of these have in common despite
their differences
Two
◦They all use ____________
possible allele types
Karyotype
Picture of homologous
chromosomes that are
arranged in order of size
A normal human Karyotype
has 44 autosomal
chromosomes and 2 sex
chromosomes
Karyotypes: can help determine
chromosomal abnormalities
Chromosomal Disorders
Nondisjunction – means “not
coming apart” – results in
abnormal numbers of
chromosomes in gametes
Monosomy – when there is a
chromosome missing
Trisomy- when there is an extra
chromosome
Sex – linked Traits
• Genes for these traits are
located only on the X
chromosome (NOT on the Y
chromosome)
• X linked alleles always show
up in males whether
dominant or recessive
because males have only
one X chromosome
Sex-Linked Inheritance
- Sex-linked genes are found on the X chromosome
- Because males have only one X chromosome, males are more
likely than females to receive & express a recessive trait.
- A person is a carrier if they have one recessive allele “and” one
dominant allele for a trait.
• Examples of recessive sex-linked disorders:
colorblindness – inability to distinguish between
certain colors
You should see 58 (upper left),
18 (upper right), E (lower left)
and 17 (lower right).
Color blindness is the inability to
distinguish the differences
between certain colors. The
most common type is red-green
color blindness, where red and
green are seen as the same
color.
hemophilia – blood won’t clot
• Examples:
Down’s syndrome – (Trisomy 21) 47 chromosomes,
extra chromosome at pair #21
Turner’s syndrome – only 45 chromosomes, missing a sex
chromosome (X)
Girls affected – short, slow growth, heart problems
Klinefelter’s syndrome – 47 chromosomes, extra X chromosomes
(XXY)
Boys affected – low testosterone levels, underdeveloped muscles,
sparse facial hair
• Having an extra set of chromosomes is fatal in animals,
but in plants it makes them larger and hardier.
Hardier
• Example: A female that has normal vision but is a carrier
for colorblindness marries a male with normal vision.
Give the expected phenotypes of their children.
N = normal vision
n = colorblindness
XN Xn X XN Y
XN
Xn
XN XNXN
XNXn
XNY
XnY
Y
Phenotype: 2 normal vision females
1 normal vision male
1 colorblind male
Autosomal Inheritance
- Traits not located on the sex chromosomes.
Autosomal Recessive
- Equal numbers of males & females affected.
- Can skip generations.
i.e. Cystic Fibrosis & Sickle Cell Anemia
Problem: A female homozygous dominant for C.F. marries a man who
is a carrier for C.F.
What are their chances of having a child with C.F.?
Autosomal Dominant / Lethal Alleles
- One dominant allele leads to death.
- Seen in every generation.
i.e. Huntington’s Disease
Problem: A female heterozygous for Huntington’s disease marries a
man who does not have the disorder. What are the chances their
child will have Huntington’s disease?
PEDIGREES
Chart that helps track which
members of a family express a trait.
Interpreting Pedigrees
STEPS:
1. Determine if its Autosomal or Sex-Linked?
- If “most” affected individuals are XY, then it is most likely X-Linked.
- If there is a 50:50 ratio of affected males to females, than it is most
likely Autosomal.
2. Is it dominant or recessive?
- If dominant, one parent must have the trait and it will be seen in
every generation.
- If recessive, neither parent has to have it and it can skip generations.
Pedigrees
• Graphic representation of how a trait is
passed from parents to offspring
• Tips for making a pedigree
1. Circles are for females
2. Squares are for males
3. Horizontal lines connecting a male and a
female represent a marriage
4. Vertical line and brackets connect parent
to offspring
5. A shaded circle or square indicates a
person has the trait
6. A circle or square NOT shaded represents
an individual who does NOT have the trait
7. Partial shade indicates a carrier –
someone who is heterozygous for the trait
• Example: Make a pedigree chart for the following
couple. Dana is color blind; her husband Jeff is not.
They have two boys and two girls.
HINT: Colorblindness is a recessive sex-linked trait.
XnXn
Has trait
XNY
Can pass trait to
offspring
Multiple Alleles
Two
- When there are more than ______________
possible alleles for a gene.
- Along with having multiple alleles, a gene
may also show incomplete or co-dominance.
What does that mean?
Many genes that control specific traits have
More than _____________
Two alleles
_______________
This means that there are far more possibilities for different
More variety
Phenotypes _______________________________
Multiple Alleles Example
Blood Types
Possible Alleles: (IA, IB, i)
IA = Type A (IAIA or IAi)
IB = Type B (IBIB or IBi)
i = Type O (ii)
IAIB = Type AB
What possible blood type(s) could a child have from the
result of a cross between a mother who is heterozygous
Type A blood and a father who is homozygous Type B
blood.
A
B
i
i
AB
Bi
Ai
Bi
D. BLOOD TYPE NOTES
A and B are codominant
AA
BB
AB
A and B are
dominant over O
AO
BO
OO
Blood Transfusion
How does this account for bloods alleles?
* A, B, and O are the alleles
* If A and B are co-dominant, then when they are
both present they will be represented with A and B
giving us blood type AB
* When A and O and B and O are present you get AO
and BO but because A and B are dominant over O, you
get blood type A and blood type B
* O blood is known as the Universal Donor.
POLYGENIC TRAITS
- A trait controlled by two or more genes.
Examples: Height, Eye Color & Skin Color
Example Genotype: EeBbYy = Hazel Eyes
• Example: A female that has normal vision but is a carrier
for colorblindness marries a male with normal vision.
Give the expected phenotypes of their children.
N = normal vision
n = colorblindness
XN Xn X XN Y
XN
Xn
XN XNXN
XNXn
XNY
XnY
Y
Phenotype: 2 normal vision females
1 normal vision male
1 colorblind male
Pedigrees
• Graphic representation of how a trait is
passed from parents to offspring
• Tips for making a pedigree
1. Circles are for females
2. Squares are for males
3. Horizontal lines connecting a male and a
female represent a marriage
4. Vertical line and brackets connect parent
to offspring
5. A shaded circle or square indicates a
person has the trait
6. A circle or square NOT shaded represents
an individual who does NOT have the trait
7. Partial shade indicates a carrier –
someone who is heterozygous for the trait
• Example: Make a pedigree chart for the following
couple. Dana is color blind; her husband Jeff is not.
They have two boys and two girls.
HINT: Colorblindness is a recessive sex-linked trait.
XnXn
Has trait
XNY
Can pass trait to
offspring
Review
Genetic Vocabulary
 Genetics: The scientific study of heredity
 Genes: Point on a chromosome that controls the trait.
 Allele: Alternate forms of a gene/factor. A or a
 Genotype: combination of alleles an organism has. (genetic
traits)
 Phenotype: How an organism appears. (physical traits)
 Dominant: An allele which is expressed (masks the other).
 Recessive: An allele which is present but remains
unexpressed (masked)
 Homozygous: Both alleles for a trait are the same.
 Heterozygous: The organism's alleles for a trait are different.
Genetic Vocabulary
Probability : The mathematical chance that an event will
happen.
Meiosis :The cell division that produces sex cells.
Mutation : A change in the type or order of the bases in
an organism DNA: deletion, insertion or substitution.
Natural Selection : The process by which organisms with
favorable traits survive and reproduce at a higher rate
than organisms without favorable traits.
Evolution :The process by which population accumulate
inherited changes over time.
Summary of Mendel’s laws
LAW
DOMINANCE
SEGREGATION
INDEPENDENT
ASSORTMENT
PARENT
CROSS
OFFSPRING
TT x tt
tall x short
100% Tt
tall
Tt x Tt
tall x tall
75% tall
25% short
RrGg x RrGg
round & green
x
round & green
9/16
pods
3/16
pods
3/16
pods
1/16
pods
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round seeds & green
round seeds & yellow
wrinkled seeds & green
wrinkled seeds & yellow
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Dihybrid Cross
RY
Ry
rY
ry
RY
Ry
rY
ry
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Dihybrid Cross
RY
RY RRYY
Ry RRYy
rY RrYY
ry
RrYy
Ry
rY
ry
RRYy
RrYY
RrYy
RRyy
RrYy
Rryy
RrYy
rrYY
rrYy
Rryy
rrYy
rryy
Round/Yellow:
Round/green:
9
3
wrinkled/Yellow: 3
wrinkled/green:
1
9:3:3:1 phenotypic
ratio
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Dihybrid Cross
Round/Yellow: 9
Round/green:
3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1
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Test Cross
A mating between an individual of unknown genotype and a
homozygous recessive individual.
Example: bbC__ x bbcc
BB = brown eyes
Bb = brown eyes
bb = blue eyes
CC = curly hair
Cc = curly hair
cc = straight hair
bC
b___
bc
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Test Cross
Possible results:
bc
bC
b___
C
bbCc
bbCc
or
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bc
bC
b___
c
bbCc
bbcc
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Incomplete Dominance
and
Codominance
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Incomplete Dominance
F1 hybrids have an appearance somewhat in
between the phenotypes of the two parental
varieties.
Example: snapdragons (flower)
red (RR) x white (rr)
r
r
RR = red flower R
rr = white flower
R
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Incomplete Dominance
r
r
R Rr
Rr
R Rr
Rr
produces the
F1 generation
All Rr = pink
(heterozygous pink)
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Incomplete Dominance
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Codominance
Two alleles are expressed (multiple alleles) in
heterozygous individuals.
Example: blood type
1.
2.
3.
4.
type A
type B
type AB
type O
=
=
=
=
IAIA or IAi
IBIB or IBi
IAIB
ii
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Codominance Problem
Example: homozygous male Type B (IBIB)
x
heterozygous female Type A (IAi)
IA
i
IB
IAIB
IBi
IB
IAIB
IBi
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1/2 = IAIB
1/2 = IBi
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Another Codominance Problem
• Example: male Type O (ii)
x
female type AB (IAIB)
IA
IB
i
IAi
IBi
i
IAi
IBi
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1/2 = IAi
1/2 = IBi
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Codominance
Question:
If a boy has a blood type O and
his
sister has blood type AB,
what are
the genotypes and
phenotypes
of their parents?
boy - type O (ii) X girl - type AB (IAIB)
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Codominance
Answer:
IA
IB
i
i
IAIB
ii
Parents:
genotypes = IAi and IBi
phenotypes = A and B
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Sex-linked Traits
Traits (genes) located on the sex
chromosomes
Sex chromosomes are X and Y
XX genotype for females
XY genotype for males
Many sex-linked traits carried on X
chromosome
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Sex-linked Traits
Example: Eye color in fruit flies
Sex Chromosomes
fruit fly
eye color
XX chromosome - female
Xy chromosome - male
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Sex-linked Trait Problem
Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female)
XRY
x
XrXr
Remember: the Y chromosome in males does not carry
traits.
RR = red eyed
r
r
X
X
Rr = red eyed
rr = white eyed
XR
XY = male
XX = female
Y
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Sex-linked Trait Solution:
Xr
XR
XR
Xr
Y
Xr Y
Xr
XR
Xr
Xr Y
50% red eyed
female
50% white eyed
male
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Female Carriers
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Genetic Practice Problems
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Breed the P1 generation
tall (TT) x dwarf (tt) pea plants
t
t
T
T
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Solution:
tall (TT) vs. dwarf (tt) pea plants
t
t
T
Tt
Tt
produces the
F1 generation
T
Tt
Tt
All Tt = tall
(heterozygous tall)
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Breed the F1 generation
tall (Tt) vs. tall (Tt) pea plants
T
t
T
t
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Solution:
tall (Tt) x tall (Tt) pea plants
T
t
T
TT
Tt
t
Tt
tt
produces the
F2 generation
1/4 (25%) = TT
1/2 (50%) = Tt
1/4 (25%) = tt
1:2:1 genotype
3:1 phenotype
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