This unit will review the findings
of Gregor Mendel and his pea
plants and how Punnett squares
and pedigrees can help us study
genetics.
On the following slides, the red
sections highlight the key points.
Underlined words = Vocabulary!
Hyperlinks are in blue.
UNIT 11 - GENETICS
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Find Someone Who
1. Knows the meaning of the term
“dominant”?
2. Knows the meaning of the term
“homozygous”?
3. Knows the meaning of the term
“heterozygous”?
4. Knows the difference between the
term “genotype” and the term
“phenotype” using the diagram to
the left?
5. Knows what a Punnett Square
does?
"Punnett squares in genetic crossings." Biology. Ed. Richard
Robinson. New York: Macmillan Reference USA, 2010. Science
in Context. Web. 14 Jan. 2014.
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What is heredity?
 Heredity is the
passing of traits
from parents to
offspring through
their gametes.
 Here is the family
of Queen Victoria,
the British
monarch known
for carrying the
mutation for
hemophilia.
http://education.ucsb.edu/webdata/instruction/hss/Inquiry/SST_inquiry_Examples/Queen_Victori
a/victoria_fam_1894_coburg.jpg
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 Remember Queen Victoria? Here is her family pedigree
showing the disorder hemophilia. Image
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http://www.mcw.edu/cellbio/colorvision/images/pedigree.jpg
What is a pedigree?
 A pedigree shows the
relationships within a
family and can track the
appearance of a genetic
trait, disease or disorder.
• Boxes represent
males; circles
represent females.
• A pedigree always
has a key.
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Knowledge Check
How many
generations does this
pedigree show?
How many
individuals in this
pedigree are affected
by a genetic
disorder?
Is this disorder a
dominant disorder?
Explain. Turn and
talk to your
neighbor.
"pedigree." Experiment Central. U*X*L, 2010. Science in Context. Web. 14 Jan.
2014.
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Review Slides
Slides 10 through 20 are review slides from middle
school genetics. Our genetics pre-test will give you
feedback on your knowledge of these slides; if you
pass with 85% accuracy, you would NOT need to copy
these slides, only review them.
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Mendel: The Father of Genetics
 An Austrian monk named Gregor
Mendel performed experiments
during the 1800s to understand
the process of traits.
• Traits are the specific
characteristics of an organism
(blue eyes, brown hair, etc).
• Mendel used pea plants from
his garden to study.
• He noticed that sometimes the
“parent” pea plants did not
match the characteristics in
“children.”
http://dogfoose.files.wordpress.com/2008/10/14-15-pea-plants.jpg
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Mendel’s Experiments
 Mendel studied the plants and found
variations, or differences.
• EX Purple or white flowers, tall
or short plants, and even round
versus wrinkled peas.
 He crossed (or pollinated) plants
with different traits and studied the
results.
http://www.micro.utexas.edu/courses/levin/bio304/gen
etics/mendel.gif
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Mendel’s Experiments Cont.
 He found that ALL purple flowers,
round peas, and tall plants were the
MOST common (called the F1
generation or first generation).
 In the second cross, the F2
generation, Mendel observed
differences (white flowers, wrinkled
peas, short plants).
 He concluded that some traits only
appear under certain conditions.
http://www.groundscience.com/solutionsnewsletter/so
lutions15/pea.jpg
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Mendel’s Experiments Cont.
Genotype & Phenotype
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http://bio1151.nicerweb.com/doc/class/bio1151/Locked/media/ch14/14_06PhenotypeVsGenotype_L.jpg
Genotype vs. Phenotype
 The genetic makeup and inherited combination of alleles is known as
the offspring’s genotype, or “the letters that you GET.”
• EX “Tt” or “tt”
 The physical characteristic and the appearance shown in the
organism (purple flowers, blue eyes, etc) is called the phenotype.
 The phenotype is the “PROOF” of the allele that is there and is what
you “SEE”.
• EX “Tall plant” or “short plant”
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What are
alleles?
"Widow's Peak." Experiment Central. U*X*L, 2010. Science
in Context. Web. 8 Jan. 2014.
 Genes are sequences of DNA that codes for a protein and determines a
trait (EX the protein for brown fur; blue eyes).
 The different forms (options) of a gene are known as alleles.
• EX widows peak versus no widows peak
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Rule of Dominance
 The stronger trait that will
always appear is the
dominant allele (shown with
a capital letter).
 The allele that did not
appear, sometimes called
the hidden trait, is called
recessive (shown with a
lowercase letter).
Detached earlobes are a dominant allele;
attached earlobes are recessive.
Illustration by Temah Nelson.
"earlobes." Experiment Central. U*X*L, 2010. Science
in Context. Web. 8 Jan. 2014.
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Homozygous vs. Heterozygous
Sketch the following!
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 An organism can be
homozygous dominant or
homozygous recessive if they
have two identical alleles for a
trait.
• From Greek, homos - the
same
• Homozygous dominant (AA)
• Homozygous recessive (aa)
• The recessive allele can
ONLY be seen in the
homozygous form
(normally HIDDEN).
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http://www.plant.uoguelph.ca/research/b
iotech/haploid/homo.gif
What is Homozygous?
What is Heterozygous?
 An organism with a mixed
allele pair is heterozygous
(Aa) and often called a hybrid
has the opportunity of having
offspring with both traits.
• If two heterozygous
organisms cross, you can
have offspring that exhibit
(or show) the recessive
trait.
http://www.plant.uoguelph.ca/research/biotech/haploid/homo.gif
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What is a Punnett Square?
 Reginald Punnett is one of the
most “unknown” well-known
scientists because he
developed the Punnett square
to model genetic probability.
 He published Mendelism in
1905 to explain the concepts
of Mendelian genetics.
 A Punnett square is a chart
used to predict and compare
the genetic combinations that
will result from sexual
reproduction.
"Punnett Squares." Genetics. Ed. Richard Robinson.
New York: Macmillan Reference USA, 2010. Science in
Context. Web. 8 Jan. 2014.
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Punnett Squares Cont.
 In the Punnett square here, you
can visualize the genes the parents
are passing to offspring.
• Each square of the box
represents 1 offspring (or
child).
• Each parent donates 1 allele.
• The dominant (capital) allele
will always go first, and will
always be seen in the
organism.
"Punnett squares in genetic crossings." Biology.
Ed. Richard Robinson. New York: Macmillan
Reference USA, 2010. Science in Context. Web. 8
Jan. 2014.
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Knowledge Check
Why is the Punnett Square
to the left called a
“monohybrid cross”? How
many offspring will display
the dominant trait versus
the recessive trait? What
genotypic ratio will be seen
in the offspring? Turn and
talk to your neighbor.
"Punnett Square with Monohybrid Cross." Science Online.
Facts On File, Inc. Web. 14 Jan. 2014.
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Knowledge Check
In screech owls, red feathers (F) are dominant over gray feathers
(f). If two heterozygous red-feathered owls are mated, what
percentage of their offspring would be expected to have red
feathers? Use the chalk and complete the cross!
http://exchangedownloads.smarttech.com/public/content/73/7
31dc772-fd50-4973-a24292b232ea9aaa/previews/medium/0001.png
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Knowledge Check
http://exchangedownloads.smarttech.com/p
ublic/content/73/731dc772-fd50-4973-a24292b232ea9aaa/previews/medium/0001.png
In watermelon plants the allele for solid green fruit (G) is dominant
over the allele for striped fruit (g). Pollen from a flower of a
homozygous green watermelon plant is used to pollinate a flower
from a heterozygous green watermelon plant. What percent of the
offspring of this cross will bear striped watermelons? Use the chalk
and complete the cross!
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Incomplete Dominance
http://www.gwu.edu/~darwin/BiSc150/One/ro
se.GIF
 We now know that there are also instances of incomplete
dominance, where there is none that is dominant or recessive but a
mixture (blending) of both alleles.
• EX in certain flowers; a white crossed with a red can produce a
pink flower.
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Knowledge Check
If a plant producing pink flowers (RW) is allowed to self pollinate
repeatedly, what colors would be expected to be seen in the
garden? Use the chalk and complete the cross!
http://exchangedownloads.smarttech.com/public/content/73/7
31dc772-fd50-4973-a24292b232ea9aaa/previews/medium/0001.png
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Codominance
 There are also instances of codominance, where both dominant
alleles are expressed.
• EX in erminitte chickens; a white crossed with a black will
produce a chicken with both black and white feathers.
http://myloupe.com/home/info-price-rf.php?image_id=465633
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Codominance Cont.
 A chestnut horse (CBCB) crossed with a cremello horse
(CwCw) will produce a palomino horse (CBCW)
 More on horse genetics!
http://www.diamondjfarms.com/photo/c
otton(5-08)2ce.jpg
http://www.freewebs.com/horsesare
the_best/chestnut%20horse.jpg
CBCB
CWCW
CBCW
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http://www.encyclopedia.com/topic/palomino_horse.aspx
Knowledge Check
If cremello stud (CWCW) reproduces with a chestnut mare (CBCB)
what is the likelihood their foal could resemble the mother? Use
the chalk and complete the cross!
http://exchangedownloads.smarttech.com/public/content/73/7
31dc772-fd50-4973-a24292b232ea9aaa/previews/medium/0001.png
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Multiple Alleles
http://ghs.gresham.k12.or.us/science/ps/sci/soph/genetics/notes/bloodtype.htm
 Not all genes have just
two alleles for the trait;
traits with more than two
alleles are described as
having multiple alleles.
• EX Hair color, eye
color, and blood types
are all examples of
human traits with
multiple alleles.
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Multiple Alleles Cont.
 3 Alleles for Blood Type: A, B, O
 “A” and “B” are codominant over “O” which is recessive
Phenotype
Genotype
Can Receive
Blood From
Can Donate
Blood To
A
IA IA , IA i
A, O
A, AB
B
IBIB, IBi
B, O
B, AB
AB
IA IB
A, B, AB,O
AB
O
ii
O
A, B, AB, O
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Knowledge Check
If a woman with O blood (ii) reproduces with a man with AB blood
(IAIB), what phenotypes will be seen in their offspring? Use the
chalk and complete the cross!
http://exchangedownloads.smarttech.com/public/content/73/7
31dc772-fd50-4973-a24292b232ea9aaa/previews/medium/0001.png
Background Image: http://www.flowerevery.com/wp-content/uploads/2012/07/pea-plant-flower.jpg
Knowledge Check
If a woman with AB blood (IAIB) reproduces with a man with A
blood (IAi), what phenotypes will be seen in their offspring? Use
the chalk and complete the cross!
http://exchangedownloads.smarttech.com/public/content/73/7
31dc772-fd50-4973-a24292b232ea9aaa/previews/medium/0001.png
Background Image: http://www.flowerevery.com/wp-content/uploads/2012/07/pea-plant-flower.jpg
Polygenic Traits
http://www.algebralab.org/img/4
9ab8f77-f675-423a-b8afd46874987ab3.gif
 Not every trait is controlled by one gene. Traits controlled by two or
more genes are said to be polygenic traits, which means “having many
genes”.
 Human stature (or height) is controlled by multiple genes.
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Sex-Linked Genes
 Genes that are located on the X or Y chromosomes are called
sex-linked genes.
• Many sex-linked genes are found on the X chromosome
(which contains more than 100 genetic disorders).
http://anthro.palomar.edu/biobasis/images/sex_cells.gif
 Colorblindness and
hemophilia are just two
examples of genes
relating to the X
chromosome.
 The human Y
chromosome is much
smaller than the X and
only contains a few
genes.
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http://exchangedownloads.smarttech.com/public/content/73/7
31dc772-fd50-4973-a24292b232ea9aaa/previews/medium/0001.png
Knowledge Check
In red-green colorblindness, individuals cannot perceive the colors
red and green in the same way as individuals with full color vision.
Full color vision is coded by a dominant allele (B) on the X
chromosome. Red-green colorblindness is caused by a recessive
allele (b) on the X chromosome. Identify the phenotype of a
female with the genotype XBXb. Identify the phenotype of a male
with the genotype XBY. Use the chalk and complete the cross!
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http://exchangedownloads.smarttech.com/public/content/73/7
31dc772-fd50-4973-a24292b232ea9aaa/previews/medium/0001.png
Knowledge Check
Hemophilia is a bleeding disorder carried on the X chromosome
where individuals cannot create blood clots due to a missing
protein. Normal clotting is coded by a dominant allele (C) on the X
chromosome. Hemophilia is caused by a recessive allele (c) on the
X chromosome. Queen Victoria of England was a carrier for
hemophilia, XCXc. Her spouse was not, XCY. Use the chalk and
complete the cross!
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Knowledge Check
Duchenne muscular dystrophy
is a genetic disease due to the
loss-of-function mutation. The
bottom diagram shows a
typical pedigree for inheritance
of an x-linked trait such as
Duchenne muscular dystrophy.
Which sex is most affected by
this disorder? Why? How does
the Punnett square relate to the
information displayed in the
pedigree? Turn and talk to your
neighbor.
"Genetic trait of Duchenne muscular
dystrophy." Biology. Ed. Richard Robinson. New York:
Macmillan Reference USA, 2010. Science in Context.
Web. 14 Jan. 2014.
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Two Factor Cross
 We understand how a simple
Punnett square works by outlining
the possibilities for one specific
trait
• EX eye color = E’s, skin color
= G’s
 The two factor cross shows the
possibilities comparing TWO
unique traits (using two different
letters).
• Male Genotype = Gg & Ee
• Female Genotype = GG & ee
http://cosbiology.pbworks.com/f/12657
37702/9.04.DihyrbidCrossF2.JPG
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Two Factor
Step #1 – The Gametes


Remember that meiosis creates haploid gametes (sex
cells) in an organism with half the number of
chromosomes.
The first step in a two factor cross is to determine the
gametes. What genes will be held in the gametes?
• There are two ways to do this:
• The FOIL Method
• The Box Method
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FOIL Method
 FOIL is an acronym standing for first, outer, inner, and
last.
• First letters in the scenario make one gamete.
• Outer letters in the scenario make another gamete.
• Inner letters make another gamete.
• Last letters make the last gamete.
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Box Method
1.
2.
3.
4.
5.
Draw a box with 4 boxes.
Place the 1st genotype (Gg) on the top of the box.
Place 2nd genotype (Ee) on the side of the box.
Fill in the four squares.
These will be the sex cells represent meiosis and the genes
within the (gametes).
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Step #2 – The Two Factor Cross
1.
2.
Draw a Punnett square with 16 boxes.
Place the gametes on the top and sides
(red & blue)
3. Always group the same genes together
(G’s with g’s, etc).
EX – in the first box, place a GGEe.
4. Fill in the remaining boxes.
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The Dihybrid Cross
 A two factor Punnett square shows 16 possible
genotypic combinations.
Ge
Ge
Ge
Ge
GE
GGEe GGEe GGEe GGEe
gE
GgEe
Ge
GGee
ge
Ggee
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Two Factor Practice
1. Male = Heterozygous using “T”; Homo recessive using
“P”; Female = Homo dominant using “T”; Homo recessive
using “P”
2. Male = Homo recessive using “R”; Heterozygous using
“Y”; Female = Heterozygous using “R”; Hetero “Y”
3. Male = Homo dominant using “B”; Homo recessive using
“E”; Female = Heterozygous using “B”; Homo dominant
using “E”
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Gene Expression
 Multicellular organisms need a variety of cell types to
perform specific functions for the organism;
therefore, individual cells differentiate and become
specialized in structure and function.
• Differentiation happens due to selective gene
expression – some genes are turned off, some are
turned on.
 Internal and external environments can influence
gene expression.
• EX hormones, sex
• EX temperature, nutrition
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Gene Expression Example
The arctic fox only
has white fur during
the winter months,
they have brown fur
during warmer
temperatures. This
change in fur color is
an example of
controlled gene
expression.
Image
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http://ccr.coriell.org/nigms/genes/17gene.gif
What is a gene map?
 In 1911, the first chromosomal gene map
was produced and showed the gene
locations on the chromosomes of a fruit fly.
The banding areas represent a named gene
[EX NF1] that controls a specific trait(s).
 Gene maps are now widely used in
understanding genetic mutations and
sickness since the human genome project.
• You can actually download the
“GATTACA” sequence for humans at the
National Center for Biotechnology
Information.
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Gene Maps Cont.
The map is based on the idea of linkage, which means that the closer
two genes are to each other on the chromosome, the greater the
probability that they will be inherited together. By following
inheritance patterns, the relative locations of genes along the
chromosome are established.
Adapted from Genome.Gov
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