Introduction to Genetics
http://en.wikipedia.org/wiki/Mendelian_genetics
http://en.wikipedia.org/wiki/Dominance_relationship
http://en.wikipedia.org/wiki/Punnett_square
http://web.science.oregonstate.edu/bi10x/otherresources/punnett%20squares.htm
This wonderful activity developed from:
http://www.schools.utah.gov/curr/science/sciber00/7th/genetics/sciber/fnbgacti.htm
Students will:
1. Use genotype to produce phenotype on the organism “marshmallow bug” that has
two pair of chromosomes, with a total of 10 genes
2. The marshmallow bug chromosomes will undergo meiosis, and the new genetic
material will produce the next generation of offspring
3. The chromosomes will crossover.
4. The chromosomes will randomly assort.
5. Students will examine the frequency of the genotypes of the above genes through
the use of a Punnett square.
6. Students will calculate the total number of genotypic combinations possible in
this 10-gene system.
7. Students will calculate the total number of phenotypic combinations possible in
this same 10-gene system.
Benchmarks (these old standards have been superceded by the standards adopted in
2009. When completing your lab report, please apply those given you with your
syllabus:
Life Science
CCG Organisms: Understand the characteristics, structure, and functions of
organisms.
SC.03.LS.01
Recognize characteristics that are similar and different
between organisms.
SC.05.LS.01
Group or classify organisms based on a variety of
characteristics.
SC.05.LS.01.01 Classify a variety of living things into groups using
various characteristics.
CCG Heredity: Understand the transmission of traits in living things.
SC.03.LS.03
Describe how related plants and animals have similar
characteristics.
SC.05.LS.04
Describe the life cycle of an organism.
SC.05.LS.04.01 Describe the life cycle of common organisms.
SC.05.LS.04.02 Recognize that organisms are produced by living
organisms of similar kind, and do not appear
spontaneously from inanimate materials.
SC.08.LS.03
Describe how the traits of an organism are passed from
generation to generation.
SC.08.LS.03.01 Distinguish between asexual and sexual
reproduction.
1
SC.08.LS.03.02
Identify traits inherited through genes and those
resulting from interactions with the environment.
SC.08.LS.03.03 Use simple laws of probability to predict patterns of
heredity with the use of Punnett squares.
CCG Diversity/Interdependence: Understand the relationships among living
things and between living things and their environments.
SC.08.LS.05
Describe and explain the theory of natural selection as a
mechanism for evolution.
SC.08.LS.05.01 Identify and explain how random variations in
species can be preserved through natural selection.
Mathematics
Calculations and Estimations
CCG: Numbers: Understand numbers, ways of representing numbers,
relationships among numbers, and number systems.
MA.03.CE.04
Order, model, compare, and identify commonly used
fractions (halves, thirds, fourths, eighths, tenths) using
concrete models and visual representations.
MA.03.CE.05
Develop understanding of fractions as parts of unit
wholes, as parts of a collection, as locations on number
lines, and as divisions of whole numbers.
MA.04.CE.01
Read, write, order, model, and compare whole numbers
to one million, common fractions, and decimals to
hundredths.
MA.04.CE.03
Locate common fractions and decimals on a number
line.
MA.05.CE.01
Order, model, and compare common fractions,
decimals and percentages.
MA.05.CE.03
Model, recognize, and generate equivalent forms of
commonly used fractions, decimals, and percents.
MA.06.CE.01
Order, model, and compare positive rational numbers
(fractions, decimals, and percentages).
MA.06.CE.03
Understand rates and ratios as comparisons of two
quantities by division.
MA.06.CE.04
Differentiate between rates and ratios and express both
as fractions.
MA.06.CE.05
Solve problems by calculating rates and ratios.
MA.06.CE.09
Model square numbers and recognize their
characteristics.
MA.07.CE.03
Use rates, ratios, and percents to solve problems.
MA.08.CE.02
Apply proportions to solve problems.
CCG: Computation and Estimation: Compute fluently and make reasonable
estimates.
MA.03.CE.15
Identify the operation (add, subtract, multiply, or
divide) for solving a problem.
2
MA.03.CE.16
MA.03.CE.17
MA.04.CE.14
MA.04.CE.15
MA.05.CE.13
MA.06.CE.15
MA.06.CE.16
MA.06.CE.18
MA.07.CE.13
MA.08.CE.07
Develop and use strategies (overestimate,
underestimate, range of estimates) to make reasonable
estimates.
Recognize which place value will be the most helpful in
estimating an answer.
Identify the most efficient operation (add, subtract,
multiply, or divide) for solving a problem.
Select and use an appropriate estimation strategy
(overestimate, underestimate, range of estimates) based
on the problem situation when computing with whole
numbers or money amounts.
Select and use an appropriate estimation strategy
(overestimate, underestimate, range of estimates) based
on the problem situation when computing with
decimals.
Solve problems involving common percentages.
Convert mentally among common decimals, fractions
and percentages.
Develop and use strategies to estimate the results of
positive rational number computations and judge the
reasonableness of results.
Develop and use strategies to estimate the results of
integer computations and judge the reasonableness of
results.
Develop and use strategies to estimate the results of
rational number computations and judge the
reasonableness of results.
Statistics and Probability
CCG: Probability: Understand and apply basic concepts of probability.
MA.04.SP.02
Determine probability of a single event.
MA.04.SP.03
Understand that the probability of an event can be
represented by a number from 0 (impossible) to 1
(certain).
MA.05.SP.02
Connect simple fractional probabilities to events (e.g.,
heads is 1 out of 2; rolling a 5 on a six-sided number
cube is 1/6).
MA.06.SP.02
Determine experimental probability of an event from a
set of data.
MA.06.SP.03
Express probability using fractions, ratios, decimals and
percents.
MA.06.SP.04
Understand that probability cannot determine an
individual outcome, but can be used to predict the
frequency of an outcome.
MA.06.SP.05
Determine the number of possible combinations of two
or more classes of objects (e.g., shirts, pants and shoes).
3
MA.07.SP.02
Compute experimental probabilities from a set of data
and theoretical probabilities for single and simple
compound events, using various methods (e.g.,
organized lists, tree diagrams, area models).
MA.07.SP.03
Determine probabilities of simple independent and
dependent events.
MA.07.SP.04
Compare experimental probability of an event with the
theoretical probability and explain any difference.
MA.07.SP.05
Determine all possible outcomes of a particular event or
all possible arrangements of objects in a given set by
applying various methods including tree diagrams and
systematic lists.
MA.08.SP.03
Understand and use appropriate terminology to describe
complementary and mutually exclusive events and
determine their probabilities.
MA.08.SP.04
Apply theoretical probability to determine if an event or
game is fair or unfair and pose and evaluate
modifications to change the fairness.
CCG: Collect and Display Data: Formulate questions that can be addressed with
data and collect, organize, and display relevant data to answer them.
MA.03.SP.02
Ask and answer simple questions that can be answered
by collecting, organizing and displaying data.
MA.03.SP.03
Represent and interpret data using tally charts,
pictographs, and bar graphs, including identifying the
mode and range.
MA.04.SP.04
Conduct experiments and simulations to determine
experimental probability of different outcomes.
MA.04.SP.05
Represent and interpret data collected from probability
experiments and simulations using tallies, charts,
pictograms, and bar graphs, including determining
probabilities of single events.
MA.05.SP.03
Design investigations to address a question and
recognize how data collection methods affect the nature
of a set of data.
MA.05.SP.04
Understand basic concepts of sampling (e.g., larger
samples yield better results, the need for representative
samples).
MA.05.SP.05
Represent and interpret data using tables, circle graphs,
bar graphs, and line graphs or plots (first quadrant).
MA.05.SP.06
Compare different representations of the same data and
evaluate how well each representation shows important
aspects of the data (e.g., circle and bar graphs,
histograms with different widths).
MA.05.SP.07
Evaluate the appropriateness of representations of
categorical and numeric data (e.g., categorical: types of
4
lunch food; and numerical: heights of students in a
class).
MA.06.SP.06
Design experiments and simulations to determine
experimental probability of different outcomes.
MA.06.SP.07
Understand that experimental probability approaches
theoretical probability as the number of trials increases.
MA.06.SP.08
Recognize and understand the connections among
concepts of independent outcomes, picking at random,
and fairness.
MA.06.SP.09
Represent and interpret the outcome of a probability
experiment using a frequency distribution, including
determining experimental probabilities.
MA.07.SP.06
Formulate questions and design experiments or surveys
to collect relevant data.
MA.07.SP.07
Identify situations in which it makes sense to sample
and identify methods for selecting a sample (e.g.,
convenience sampling, responses to survey, random
sampling) that are representative of a population.
MA.07.SP.08
Distinguish between random and biased samples and
identify possible sources of bias in sampling.
MA.07.SP.09
Represent and interpret data using frequency
distribution tables, box-and whisker-plots, stem-andleaf plots, and single- and multiple- line graphs.
MA.07.SP.10
Determine the graphical representation of a set of data
that best shows key characteristics of the data.
MA.07.SP.11
Recognize distortions of graphic displays of sets of data
and evaluate appropriateness of alternative displays.
CCG: Data Analysis and Predictions: Develop and evaluate inferences and
predictions that are based on data.
MA.03.SP.04
Draw conclusions and make predictions and inferences
from tally charts, pictographs, or bar graphs.
MA.04.SP.06
Predict the degree of likelihood of a single event
occurring using words such as certain, impossible, most
often, least often, likely, and unlikely.
MA.04.SP.07
Predict the likelihood of an outcome prior to an
experiment and compare predicted probability with the
actual results.
MA.06.SP.10
Make predictions for succeeding trials of a probability
experiment given the outcome of preceding repeated
trials.
MA.06.SP.11
Predict the outcome of a probability experiment by
computing and using theoretical probability.
MA.07.SP.12
Analyze data from frequency distribution tables, boxand whisker-plots, stem-and-leaf plots using measures
of center and spread and draw conclusions.
5
MA.08.SP.07
Estimate or predict the occurrence of future events
using data.
Mathematical Problem Solving
CCG Conceptual Understanding: Select, apply, and translate among
mathematical representations to solve problems.
MA.02.PS.01
Interpret the concepts of a problem-solving task and
translate them into mathematics.
MA.03.PS.01
Interpret the concepts of a problem-solving task and
translate them into mathematics.
MA.04.PS.01
Interpret the concepts of a problem-solving task and
translate them into mathematics.
MA.05.PS.01
Interpret the concepts of a problem-solving task and
translate them into mathematics.
MA.06.PS.01
Interpret the concepts of a problem-solving task and
translate them into mathematics.
MA.07.PS.01
Interpret the concepts of a problem-solving task and
translate them into mathematics.
MA.08.PS.01
Interpret the concepts of a problem-solving task and
translate them into mathematics.
CCG Processes and Strategies: Apply and adapt a variety of appropriate
strategies to solve problems.
MA.02.PS.02
Choose strategies that can work and then carry out the
strategies chosen.
MA.03.PS.02
Choose strategies that can work and then carry out the
strategies chosen.
MA.04.PS.02
Choose strategies that can work and then carry out the
strategies chosen.
MA.05.PS.02
Choose strategies that can work and then carry out the
strategies chosen.
MA.06.PS.02
Choose strategies that can work and then carry out the
strategies chosen.
MA.07.PS.02
Choose strategies that can work and then carry out the
strategies chosen.
MA.08.PS.02
Choose strategies that can work and then carry out the
strategies chosen.
CCG Verification: Monitor and reflect on the process of mathematical problem
solving.
MA.02.PS.03
Produce identifiable evidence of a second look at the
concepts/strategies/calculations to defend a solution.
MA.03.PS.03
Produce identifiable evidence of a second look at the
concepts/strategies/calculations to defend a solution.
MA.03.PS.03
Produce identifiable evidence of a second look at the
concepts/strategies/calculations to defend a solution.
6
MA.04.PS.03
MA.05.PS.03
MA.06.PS.03
MA.07.PS.03
MA.08.PS.03
Produce identifiable evidence of a second look at the
concepts/strategies/calculations to defend a solution.
Produce identifiable evidence of a second look at the
concepts/strategies/calculations to defend a solution.
Produce identifiable evidence of a second look at the
concepts/strategies/calculations to defend a solution.
Produce identifiable evidence of a second look at the
concepts/strategies/calculations to defend a solution.
Produce identifiable evidence of a second look at the
concepts/strategies/calculations to defend a solution.
CCG Communication: Communicate mathematical thinking coherently and
clearly. Use the language of mathematics to express mathematical ideas
precisely.
MA.02.PS.04
Use pictures, symbols, and/or vocabulary to convey the
path to the identified solution.
MA.03.PS.04
Use pictures, symbols, and/or vocabulary to convey the
path to the identified solution.
MA.04.PS.04
Use pictures, symbols, and/or vocabulary to convey the
path to the identified solution.
MA.05.PS.04
Use pictures, symbols, and/or vocabulary to convey the
path to the identified solution.
MA.06.PS.04
Use pictures, symbols, and/or vocabulary to convey the
path to the identified solution.
MA.07.PS.04
Use pictures, symbols, and/or vocabulary to convey the
path to the identified solution.
MA.08.PS.04
Use pictures, symbols, and/or vocabulary to convey the
path to the identified solution.
CCG: Accuracy: Accurately solve problems that arise in mathematics and other
contexts.
MA.02.PS.05
Accurately solve problems using mathematics.
MA.03.PS.05
Accurately solve problems using mathematics.
MA.04.PS.05
Accurately solve problems using mathematics.
MA.05.PS.05
Accurately solve problems using mathematics.
MA.06.PS.05
Accurately solve problems using mathematics.
MA.07.PS.05
Accurately solve problems using mathematics.
MA.08.PS.05
Accurately solve problems using mathematics.
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Materials (for 30 students working with a partner)
Permanent
Consumable
 15 Pennies
 Pencils
 15 Red dice
 Genotype to Phenotype handout
 15 Green dice
 “Chromosomes” copies-2 colors
to indicate “Father” and
 15 Scissors
“Mother”
 15 - 4x4 Punnett Squares boards

Large marshmallows
 15 - 8x8 Punnett Squares boards
 Small color marshmallows
 15 - 16x16 Chess boards
 Chocolate chips
 ~2000 Red poker chips
 Licorice whips – red and black
 ~2000 Blue poker chips
 Twizzle pull-apart– pink and red
 ~2000 Green poker chips
 Butterscotch chips
o or any other kind of token in
3 colors
 Frosting (chocolate, lemon, and
vanilla)
 Plastic knives
 Wax paper
 Sandwich plastic bags
Discussion:
Although it seems a circuitous route to DNA fingerprints, following these steps allow
students to visualize and comprehend exactly how DNA varies individually. They model
crossover and independent assortment of genetic material. From this step, students next
learn that this variation is carried by DNA base pairs. DNA code is the 4 molecules of
adenine (A), Thymine (T), cytosine (C), and guanine (G), and we know that A pairs with
T, C pairs with T. DNA sequences are the instructions for primarily proteins, and
proteins make us. If the DNA (genotype) varies, that translates in how the organism
looks or functions (phenotype). Both elementary and middle school students gain a
deeper understanding of this whole process, either building a foundation, or expanding
their present understanding.
Your focus for this class is pretty clear, but you can also incorporate INDEPENDENT
ASSORTMENT, a particularly difficult concept. For older students, emphasize
replicated chromosome pairs crossover and exchange genetic material between the
homologous pairs before the chromosomes randomly assort. For younger students, you
can actually simulate meiosis with your paper chromosome pairs, separating mom and
dad first into two “cells,” and then separate the replicated DNA into a total of 4 cells.
Depending on the sophistication of your middle school students, you may also want to
simulate meiosis by actually replicating your DNA, dividing the homologous pairs, and
then dividing the replicated pairs. To emphasize independent assortment, use a coin to
determine if a particular chromosome goes to the cell on the left or the cell on the right.
One of the benchmarks is use of Punnett squares. This is a perfect time to meet that
particular benchmark, and hence Activity 2. You can start with 1 gene – nose color or
antenna number, and determine the number of offspring that will have the dominant and
how many will have the recessive phenotype. Second, examine for two genes – for
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example the number and color of legs, which in our simulation are controlled by two
different genes on two different chromosomes. Ask the middle school students how
many squares would be needed to work out the phenotypic ratios for 3 genes (64 squares,
or a grid that is 8 x 8 squares). Have the students try out different combinations (for
example, one parent is homozygous for the recessive traits and the other parent is
heterozygous) and determine the frequency of genotypes. For your advanced students,
challenge them to determine the total number of possible outcomes and correctly find the
phenotypic ratios for 4 genes.
Finally, students LOVE building the marshmallow bugs (however, I do not let them eat
their bugs until the end of class). Before you teach this lesson, you need to find out if any
of your students are vegetarian or vegan. Trader Joes carries vegan marshmallows.
This unit can be taught in a 90-minute class by streamlining the activities, and
introducing genetics with the focus solely on variation in a population. It can also be
extended to two 90-minute classes by following the extended activities and discussing the
concepts more fully, especially sample size, probability, and meiosis.
Overview of Activities:
 Using “independent assortment,” students assigned alleles to two different pair of
chromosomes, determine the genotype and build the phenotype of a marshmallow
bug. The bug chromosomes undergo meiosis, forming 4 new “cells.” They keep
one of these “cells” and receive another “cell.” The two cells fuse, and the
students determine the genotype and build the phenotype of the offspring. About
1 hour.
 Students, using a Punnett square, determine the frequency that an offspring will
show recessive traits for a single trait, and then two traits. Run these examples
using both parents as heterozygous for the alleles. Additional examples start with
a parent recessive homozygous for an allele, or both parents homozygous, one
dominant and the other recessive, to determine the frequency of the homozygous
dominant, homozygous recessive and heterozygous states for a single allele, or
two alleles. About 30 minutes.
Set-up for class (of 30):
Students work with a partner, but everyone participates with their own analysis
 Set out for each pair of students:
 15 pennies
 15 red dice
 15 blue dice
 15 Scissors
 15 “Cells”
 15 Genotype to Phenotype handout
 15 Pencils
 blank “Chromosomes”
 15 large sheets wax paper
9


30 sandwich plastic bags
Put in convenient location but away from students:
 15 Punnett Squares boards
 Poker chips (divided into 15 piles of ~125 - 150 for each color)
 Large marshmallows
 Small color marshmallows
 Chocolate chips
 Licorice whips – red and black
 Twizzle pull-apart and cut into 1” pieces – pink and red
 Butterscotch chips
 frosting
 plastic knives
10
Marshmallow Bug Genetics Activity 1
Supplies:
 Pennies
 Wooden cubes
 Scissors
 “Cells”
 Genotype to Phenotype handout
 Pencils
 “Chromosomes”
 Large marshmallows
 Small color marshmallows
 Chocolate chips
 Licorice whips – red and black
 Twizzle pull-apart– pink and red
 Butterscotch chips
 Vanilla frosting
 Chocolate frosting
 Plastic knives
 Wax paper
 Sandwich plastic bags
Discussion:
Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets
relating to the transmission of hereditary characteristics from parent organisms to their
children; it underlies much of genetics. They were initially derived from the work of
Gregor Mendel published in 1865 and 1866 which was "re-discovered" in 1900, and were
initially very controversial. When they were integrated with the chromosome theory of
inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics.
History
The laws of inheritance were derived by Gregor Mendel, a 19th century Moravian monk
conducting plant hybridity experiments. Between 1856 and 1863, he cultivated and tested
some 28,000 pea plants. His experiments brought forth two generalizations which later
became known as Mendel's Laws of Heredity or Mendelian inheritance. These are
described in his essay "Experiments on Plant Hybridization" that was read to the Natural
History Society of Brno on February 8 and March 8, 1865, and was published in 1866.
Mendel's results were largely rejected. Though they were not completely unknown to
biologists of the time, they were not seen as being crucial. Even Mendel himself did not
see their ultimate applicability, and thought they only applied to certain categories of
species. In 1900, however, the work was "re-discovered" by three European scientists,
Hugo de Vries, Carl Correns, and Erich von Tschermak. The exact nature of the "rediscovery" has been somewhat debated: De Vries published first on the subject, and
Correns pointed out Mendel's priority after having read De Vries's paper and realizing
11
that he himself did not have priority, and De Vries may not have acknowledged truthfully
how much of his knowledge of the laws came from his own work, or came only after
reading Mendel's paper. Later scholars have accused Von Tschermak of not truly
understanding the results at all.
Regardless, the "re-discovery" made Mendelism an important but controversial theory. Its
most vigorous promoter in Europe was William Bateson, who coined the term "genetics",
"gene", and "allele" to describe many of its tenets. The model of heredity was highly
contested by other biologists because it implied that heredity was discontinuous, in
opposition to the apparently continuous variation observable. Many biologists also
dismissed the theory because they were not sure it would apply to all species, and there
seemed to be very few true Mendelian characters in nature. However later work by
biologists and statisticians such as R.A. Fisher showed that if multiple Mendelian factors
were involved for individual traits, they could produce the diverse amount of results
observed in nature. Thomas Hunt Morgan and his assistants would later integrate the
theoretical model of Mendel with the chromosome theory of inheritance, in which the
chromosomes of cells were thought to hold the actual hereditary particles, and create
what is now known as classical genetics, which was extremely successful and cemented
Mendel's place in history.
Mendel's findings allowed other scientists to simplify the emergence of traits to
mathematical probability. A large portion of Mendel's findings can be traced to his choice
to start his experiments only with true breeding plants. He also only measured absolute
characteristics such as color, shape, and position of the offspring. His data was expressed
numerically and subjected to statistical analysis. This method of data reporting and the
large sampling size he used gave credibility to his data. He also had the foresight to look
through several successive generations of his pea plants and record their variations.
Without his careful attention to procedure and detail, Mendel's work could not have had
the impact it made on the world of genetics.
The Law of Segregation, also known as Mendel's First Law, essentially has four parts.
1. Alternative versions of genes account for variations in inherited
characteristics. This is the concept of alleles. Alleles are different versions of
genes that impart the same characteristic. For example, each human has a gene
that controls eye color, but there are variations among these genes in accordance
with the specific color for which the gene "codes".
2. For each characteristic, an organism inherits two alleles, one from each
parent. This means that when somatic cells are produced from two alleles, one
allele comes from the mother and one from the father. These alleles may be the
same (true-breeding organisms/homozygous e.g. ww and rr in Fig. 3), or different
(hybrids/heterozygous, e.g. wr in Fig. 3).
3. If the two alleles differ, then one, the allele that encodes the dominant trait, is
fully expressed in the organism's appearance; the other, the allele encoding
the recessive trait, has no noticeable effect on the organism's appearance. In
other words, only the dominant trait is seen in the phenotype of the organism.
12
This allows recessive traits to be passed on to offspring even if they are not
expressed. Not all traits have a dominant-recessive relationship, however. The
"Japanese wonder flower" Mirabilis jalapa illustrates incomplete dominance
(Figure 3). There is also codominance e.g. Human blood types where A and B are
codominant and O is recessive.
4. The two alleles for each characteristic segregate during gamete production.
This means that each gamete will contain only one allele for each gene. This
allows the maternal and paternal alleles to be combined in the offspring, ensuring
variation.
N.B It is often misconstrued that the gene itself is dominant, recessive, codominant, or
incompletely dominant. It is, however the trait, or gene product that the allele encodes
that is dominant, etc.
Figure 1: Dominant and recessive phenotypes.
(1) Parental generation. (2) F1 generation. (3) F2
generation. Dominant (red) and recessive (white)
phenotype look alike in the F1 (first) generation and
show a 3:1 ratio in the F2 (second) generation
Figure 2: The color alleles of Mirabilis jalapa are not
dominant or recessive.
(1) Parental generation. (2) F1 generation. (3) F2
generation. The "red" and "white" allele together make
a "pink" phenotype, resulting in a 1:2:1 ratio of
red:pink:white in the F2 generation.
Law of Independent Assortment
The Law of Independent Assortment, also known as "Inheritance Law" or Mendel's
Second Law, states that the inheritance pattern of one trait will not affect the inheritance
pattern of another. While his experiments with mixing one trait always resulted in a 3:1
ratio (Fig. 1) between dominant and recessive phenotypes, his experiments with mixing
two traits (dihybrid cross) showed 9:3:3:1 ratios (Fig. 2). But the 9:3:3:1 table shows that
each of the two genes are independently inherited with a 3:1 ratio. Mendel concluded that
different traits are inherited independently of each other, so that there is no relation, for
example, between a cat's color and tail length. This is actually only true for genes that are
not linked to each other.
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The reason for these laws is found in the nature of the cell nucleus. It is made up of
several chromosomes carrying the genetic traits. In a normal cell, each of these
chromosomes has two parts, the chromatids. A reproductive cell, which is created in a
process called meiosis, usually contains only one of those chromatids of each
chromosome. By merging two of these cells (usually one male and one female), the full
set is restored and the genes are mixed. The resulting cell becomes a new embryo. The
fact that this new life has half the genes of each parent (23 from mother, 23 from father
for total of 46) is one reason for the Mendelian laws. The second most important reason
is the varying dominance of different genes, causing some traits to appear unevenly
instead of averaging out (whereby dominant doesn't mean more likely to reproduce recessive genes can become the most common, too).
There are several advantages of this method (sexual reproduction) over reproduction
without genetic exchange:
1. Instead of nearly identical copies of an organism, a broad range of offspring
develops, allowing more different abilities and evolutionary strategies.
2. There are usually some errors in every cell nucleus. Copying the genes usually
adds more of them. By distributing them randomly over different chromosomes
and mixing the genes, such errors will be distributed unevenly over the different
children. Some of them will therefore have only very few such problems. This
helps reduce problems with copying errors somewhat.
3. Genes can spread faster from one part of a population to another. This is for
instance useful if there's a temporary isolation of two groups. New genes
developing in each of the populations don't get reduced to half when one side
replaces the other, they mix and form a population with the advantages of both
sides.
4. Sometimes, a mutation (e. g. Sickle Cell Anemia) can have positive side effects
(in this case Malaria resistance). The mechanism behind the Mendelian laws can
make it possible for some offspring to carry the advantages without the
disadvantages until further mutations solve the problems.
Mendelian trait
A Mendelian trait is one that is controlled by a single locus and shows a simple
Mendelian inheritance pattern. In such cases, a mutation in a single gene can cause a
disease that is inherited according to Mendel's laws. Examples include sickle-cell anemia,
Tay-Sachs disease, cystic fibrosis and xeroderma pigmentosa. A disease controlled by a
single gene contrasts with a multi-factorial disease, like arthritis, which is affected by
several loci (and the environment) as well as those diseases inherited in a non-Mendelian
fashion. The Mendelian Inheritance in Man database is a catalog of, among other things,
genes in which Mendelian mutants causes disease.
In Genetics, dominance describes a specific relationship between the effects of different
versions of a gene (alleles) on a trait or phenotype. Animals (including humans) and
plants are ‘diploid’ (see ploidy), with two copies of each gene, one inherited from each
parent. If the two copies are not identical (not the same allele), their combined effect may
be different than the effect of having two identical copies of one or the other allele. But if
14
the combined effect is the SAME as the effect of having two copies of one of the alleles,
we say that allele’s effect is dominant over the other.
For example, having two copies of one allele of the EYCL3 gene causes the eye’s iris to
be brown and having two copies of another allele causes the iris to be blue. Because
having one copy of each allele causes brown eyes, the brown allele is said to be dominant
over the blue allele (and the blue allele is said to be recessive to the brown allele).
We now know that in most cases a dominance relationship is seen when the recessive
allele is defective. In these cases a single copy of the normal allele produces enough of
the gene’s product to give the same effect as two normal copies, and so the normal allele
is described as being dominant to the defective allele. This is the case for the eye color
alleles described above, where a single functional copy of the ‘brown’ allele causes
enough melanin to be made in the iris that the eyes appear brown even when paired with
the non-melanin-producing ‘blue’ allele.
Dominance was discovered by Mendel, who introduced the use of uppercase letters to
denote ‘dominant alleles’ and lowercase to denote ‘recessive alleles’, as is still commonly
used in introductory genetics courses (e.g. B b for alleles causing brown and blue eyes).
Although this usage is convenient it is misleading, because dominance is not a property
of an allele considered in isolation but of a relationship between the effects of two alleles.
When geneticists loosely refer to a dominant allele or a recessive allele, they mean that
the allele is dominant or recessive to the standard allele.
Geneticists often use the term dominance in other contexts, distinguishing between
simple or complete dominance as described above, and other relationships. Relationships
described as incomplete or partial dominance are usually more accurately described as
giving an intermediate or blended phenotype. The relationship described as codominance
describes a relationship where the distinct phenotypes caused by each allele are both seen
when both alleles are present.
Genes are indicated in shorthand by a combination of one or a few letters - for example,
in cat coat genetics the alleles Mc and mc (for "mackerel tabby") play a prominent role.
Alleles producing dominant traits are denoted by initial capital letters; those that confer
recessive traits are written with lowercase letters. The alleles present in a locus are
usually separated by a slash; in the Mc - mc case, the dominant trait is the "mackerelstripe" pattern, and the recessive one the "classic" or "oyster" tabby pattern, and thus a
classical-pattern tabby cat would carry the alleles mc/mc, whereas a mackerel-stripe
tabby would be either Mc/mc or Mc/Mc.
Humans have 23 homologous chromosome pairs (22 pairs of autosomal chromosomes
and two distinct sex chromosomes, X and Y). It is estimated that the human genome
contains 20,000-25,000 genes. Each chromosomal pair has the same genes, although it is
generally unlikely that homologous genes from each parent will be identical in sequence.
The specific variations possible for a single gene are called alleles: for a single eye-color
gene, there may be a blue eye allele, a brown eye allele, a green eye allele, etc.
Consequently, a child may inherit a blue eye allele from their mother and a brown eye
15
allele from their father. The dominance relationships between the alleles control which
traits are and are not expressed.
An example of an autosomal dominant human disorder is Huntington's disease, which is
a neurological disorder resulting in impaired motor function. The mutant allele results in
an abnormal protein, containing large repeats of the amino acid glutamine. This defective
protein is toxic to neural tissue, resulting in the characteristic symptoms of the disease.
Hence, one copy suffices to confer the disorder.
Directions:
1) Students cut out the two pairs of chromosomes, one from each of the 2 colors of
paper, for example yellow and green. Note that yellow Paternal Chromosome 1 is
a homologous pair with green Maternal Chromosome 1. The yellow Paternal
Chromosome 2 is a homologous pair with Maternal Chromosome 2.
2) Starting with one color (in this example, the green), ask students to flip their
penny. If the penny lands as a “heads,” they will identify the character trait as a
capital letter. If it lands as “tails,” they will identify the character trait as a small
letter. They are only working with one chromosome at this point. If, for
example, the student rolls a TTHTTHTHTH, he/she would letter the chromosome
as “naBseLrCtG” in the appropriate row for the chromosomes 1 and 2.
a) Extension: As a class, build a table with columns labeled “student,” “# heads,”
and “# tails.,” Put each student’s name as the row. Ask the class what is the
probability for flipping heads? What is the probability for flipping tails. Ask
each student to record the total number of times that student flipped heads,
and flipped tails. Add the individual heads flipped and tails flipped for a class
total. . Which comes closer to the predicted probability of rolling a head 1 out
of 2 times, the individual results or the class results? Why? Discuss the
importance of a large enough sample size to reduce individual natural
variation in any probability.
3) Using the Genotype to Phenotype handout, the student records the genes in the
appropriate column for the green chromosomes and the yellow chromosomes.
4) Using the information on the left column of their Genotype to Phenotype handout,
students record the phenotype in the appropriate column.
5) Using the phenotype, students gather the materials to build their marshmallow
bug. DO NOT LET THEM EAT IT AT THIS TIME!!! The gender frosting is to
hold all the different parts together.
6) Now we want to bugs to breed (tee hee hee hee). Students take 4 blank
chromosomes 1 and 2, two yellow, two green (following the maternal and
paternal lines of inheritance).
7) NOTE TO INSTRUCTOR: The next directions are to model meiosis. For
elementary students, the steps are streamlined, beginning with the first indented
direction.
8) Replicating DNA - Have the students copy the allele codes from their parent
chromosome to the blank chromosomes, matching colors. Cut the chromosomes
out (if this hasn’t already been done). You will now have 2 copies of paternal
16
chromosome 1, 2 copies of maternal chromosome 1, 2 copies of paternal
chromosome 2, and 2 copies of maternal chromosome 2.
9) Crossover – Each student has a red die and a blue die. Students roll the 2 dice,
working with one homologous pair (for example, the paternal and maternal
chromosome 1 pair). The dice have gene numbers on them. The number rolled
are the genes exchanged during crossover. For example, if one die has 2 and the
other die has 4&5, the student would cut out those genes on each of the pair of
chromosomes, swap them and tape them back together. Repeat for Chromosome
2. You only need to have 1 pair of the replicated chromosomes crossover for this
demonstration.
10) Prophase I – stack the 4 cells, stack the replicated chromosomes and place in the
cell.
11) Metaphase I – line up the chromosomes so that paternal and maternal Chromsome
1 are next to each other, and paternal and maternal Chromsome 2 are next to each
other. Flip a coin. If heads, place paternal chromsome 1 on the left and maternal
chromosome 1 on the right. If tails, place the paternal Chromosome on the right.
Repeat for Chromosome 2.
12) Anaphase I – Separate maternal and
paternal chromesomes on top of the cells,
separating two of the stacked cells from the
other two.
13) Telophase I – Completely separate the two
stacked cells.
14) Metaphase II – line the chromosomes up for
both cells. Flip a coin. If heads, place crossover chromsome 1 on the left and
non-crossover chromosome 1 on the right. If tails, place the non-crossover
Chromosome on the right. Repeat for Chromosome 2.
15) Anaphase II –Separate the chromesomes on top of the cells, separating two of the
stacked cells from the other two.
16) Telophase I – Completely separate the 4 stacked cells.
i) For younger students, skip the crossover steps, but model the rest of
meiosis.
17) Collect 3 of the 4 cells’ chromosomes from all the students. Randomly assign
each person a different set of chromosomes. Be sure that the students does not get
one of their own sets.
18) Repeat steps 3 – 5 to produce offspring.
19) Have the students try to find identical marshmallow bugs. Remind them that
“almost the same” is NOT identical.
20) Our marshmallow bugs only have 2 pair of chromosomes with a total of 10 genes.
Humans have 23 pair of chromosomes with a total of ~ 26,000 genes! Now that
is a lot of room for variation!
a) Discuss that we have been examing organisms that have a 50% frequency of
allele N and 50% of allele n, and so on. In actuality, the frequency of alleles
can vary from population to population. This would be in preparation for the
Hardy-Weinberg Principle activity in Blood extension activity.
17
Punnett Squares Activity 2
Supplies:
 6 - 4x4 Punnett Squares boards
 6 - 8x8 Punnett Squares boards
 6 - 16x16 Chess boards
 ~800 Red poker chips
 ~800 Blue poker chips
 ~800 Green poker chips
Discussion:
The genetic combinations possible with simple dominance can be expressed by a diagram called
a Punnett square. One parent's alleles are listed across the top and the other parent's alleles are
listed down the left side. The interior squares represent possible offspring, in the ratio of their
statistical probability. In the previous example of flower color, P represents the dominant
purple-colored allele and p the recessive white-colored allele. If both parents are purple-colored
and heterozygous (Pp), the Punnett square for their offspring would be:
In the PP and Pp cases, the offspring is purple colored due to the dominant P.
P
p
Only in the pp case is there expression of the recessive white-colored phenotype.
P PP Pp
Dominant allele
p P p p p Dominant trait refers to a genetic feature that hides the recessive trait in the
phenotype of an individual. A dominant trait causes the phenotype that is seen in
a heterozygous (Aa) genotype. Many traits are determined by pairs of complementary genes,
each inherited from a single parent. Often when these are paired and compared, one allele (the
dominant) will be found to effectively shut out the instructions from the other, recessive allele.
For example, if a person has one allele for blood type A and one for blood type O, that person
will always have blood type A because it is the dominant allele. For a person to have blood type
O, both their alleles must be O (recessive). When a person has two dominant alleles, they are
referred to as homozygous dominant. If they have one dominant allele and one recessive allele,
they are referred to as heterozygous.
A dominant trait when written in a genotype is always written before the recessive gene in a
heterozygous pair. A heterozygous genotype is written Aa, not aA.
Types of dominances
Simple dominance or complete dominance
Consider the simple example of flower color in peas, first studied by Gregor Mendel. The
dominant allele is purple and the recessive allele is white. In a given individual, the two
corresponding alleles of the chromosome pair fall into one of three patterns:
 both alleles purple (PP)
 both alleles white (pp)
 one allele purple and one allele white (Pp)
18
If the two alleles are the same (homozygous), the trait they represent will be expressed. But if the
individual carries one of each allele (heterozygous), only the dominant one will be expressed.
The recessive allele will simply be suppressed.
Incomplete dominance
Discovered by Karl Correns, incomplete dominance (sometimes called partial dominance) is a
heterozygous genotype that creates an intermediate phenotype. In this case, only one allele
(usually the wild type) at the single locus is expressed, and the expression is doseage dependent.
Two copies of the gene produce full expression, while one copy of the gene produces partial
expression in an intermediate phenotype. A cross of two intermediate phenotypes (= monohybrid
heterozygotes) will result in the reappearance of both parent phenotypes and the intermediate
phenotype. There is a 1:2:1 phenotype ratio instead of the 3:1 phenotype ratio found when one
allele is dominant and the other is recessive. This lets an organism's genotype be diagnosed from
its phenotype without time-consuming breeding tests.
R
R
R'
RR RR'
R' RR' R'R'
The classic example of this is the color of carnations.
R is the allele for red pigment. R' is the allele for no pigment.
Thus, RR offspring make a lot of red pigment and appear red. R'R' offspring
make no red pigment and appear white. Both RR' and R'R offspring make some
pigment and therefore appear pink.
Codominance
In codominance, neither phenotype is completely dominant. Instead, the heterozygous individual
expresses both phenotypes. A common example is the ABO blood group system. The gene for
blood types has three alleles: A, B, and i. i causes O type and is recessive to both A and B. The A
and B alleles are codominant with each other. When a person has both an A and a B allele, the
person has type AB blood.
When two persons with AB blood type have children, the children can be type A, type B, or type
AB. There is a 1A:2AB:1B phenotype ratio instead of the 3:1 phenotype ratio found when one
allele is dominant and the other is recessive. This is the same phenotype ratio found in matings of
two organisms that are heterozygous for incomplete dominant alleles.
A
Example Punnett square for a father with A and i, and a mother with B and i:
i
B AB B
A roan horse has codominant follicle genes, expressing individual red and white
follicles.
i
A
O
Dominant negative
Most loss-of-function mutations are recessive. However, some are dominant and are called
"dominant negative" or antimorphic mutations. Typically, a dominant negative mutation occurs
when the gene product adversely affects the normal, wild-type gene product within the same cell.
This usually occurs if the product can still interact with the same elements as the wild-type
product, but block some aspect of its function. Such proteins may be competitive inhibitors of
the normal protein functions.
19
Types:


A mutation in a transcription factor that removes the activation domain, but still contains
the DNA binding domain. This product can then block the wild-type transcription factor
from binding the DNA site leading to reduced levels of gene activation.
A protein that is functional as a dimer. A mutation that removes the functional domain,
but retains the dimerization domain would cause a dominate negative phenotype, because
some fraction of protein dimers would be missing one of the functional domains.
Recessive allele
The term "recessive allele" refers to an allele that causes a phenotype (visible or detectable
characteristic) that is only seen in homozygous genotypes (organisms that have two copies of the
same allele) and never in heterozygous genotypes. Every diploid organism, including humans,
has two copies of every gene on autosomal chromosomes, one from the mother and one from the
father. The dominant allele of a gene will always be expressed while the recessive allele of a
gene will be expressed only if the organism has two recessive forms. Thus, if both parents are
carriers of a recessive trait, there is a 25% chance with each child to show the recessive trait.
The term "recessive allele" is part of the laws of Mendelian inheritance formulated by Gregor
Mendel. Examples of recessive traits in Mendel's famous pea plant experiments include the color
and shape of seed pods and plant height.
Nomenclature of recessiveness
Technically, the term "recessive gene" is imprecise because it is not the gene that is recessive but
the phenotype (or trait). It should also be noted that the concepts of recessiveness and dominance
were developed before a molecular understanding of DNA and before molecular biology, thus
mapping many newer concepts to "dominant" or "recessive" phenotypes is problematic. Many
traits previously thought to be recessive have mild forms or biochemical abnormalities that arise
from the presence of the one copy of the allele. This suggests that the dominant phenotype is
dependent upon having two dominant alleles and the presence of one dominant and one recessive
allele creates some blending of both dominant and recessive traits.
Gregor Mendel performed many experiments on pea plant (Pisum sativum) while researching
traits, chosen because of the simple and low variety of characteristics, as well as the short period
of germination. He experimented with color (green vs. yellow), size (short vs. tall), pea texture
(smooth vs. wrinkled), and many others. By good fortune, the characteristics displayed by these
plants clearly exhibited a dominant and recessive form. This is not true for many organisms.
For example, when testing the color of the pea plants, he chose two yellow plants, since yellow
was more common than green. He mated them, and examined the offspring. He continued to
mate only those that appeared yellow, and eventually, the green ones would stop being produced.
He also mated the green ones together and determined that only green ones were produced.
Mendel determined that this was because green was a recessive trait which only appeared when
yellow, the dominant trait, was not present. Also, he determined that the dominant trait would be
displayed whether or not the recessive trait was there.
Dominance/recessiveness refers to phenotype, not genotype. An example to prove the point is
sickle cell anemia. The sickle cell genotype is caused by a single base pair change in the beta-
20
globin gene: normal=GAG (glu), sickle=GTG (val). There are several phenotypes associated
with the sickle genotype:1. anemia (a recessive trait)
2. blood cell sickling (co-dominant)
3. altered beta-globin electrophoretic mobility (co-dominant)
4. resistance to malaria (dominant)
This example demonstrates that one can only refer to dominance/recessiveness with respect to
individual phenotypes.
Mechanisms of dominance
Many genes code for enzymes. Consider the case where someone is homozygous for some trait.
Both alleles code for the same enzyme, which causes a trait. Only a small amount of that enzyme
may be necessary for a given phenotype. The individual therefore has a surplus of the necessary
enzyme. Let's call this case "normal". Individuals without any functional copies cannot produce
the enzyme at all, and their phenotype reflects that. Consider a heterozygous individual. Since
only a small amount of the normal enzyme is needed, there is still enough enzyme to show the
phenotype. This is why some alleles are dominant over others.
In the case of incomplete dominance, the single dominant allele does not produce enough
enzyme, so the heterozygotes show some different phenotype. For example, fruit color in
eggplants is inherited in this manner. A purple color is caused by two functional copies of the
enzyme, with a white color resulting from two non-functional copies. With only one functional
copy, there is not enough purple pigment, and the color of the fruit is a lighter shade, called
violet.
Some non-normal alleles can be dominant. The mechanisms for this are varied, but one simple
example is when the functional enzyme is composed of several subunits. In this case, if any of
the subunits are nonfunctional, the entire enzyme is nonfunctional. In the case of a single subunit
with a functional and nonfunctional allele (heterozygous individual), the concentration of
functional enzymes is 50% of normal. If the enzyme has two identical subunits, the concentration
of functional enzyme is 25% of normal. For four subunits, the concentration of functional
enzyme is about 6% of normal. This may not be enough to produce the wild type phenotype.
There are other mechanisms for dominant mutants.
Other factors
It is important to note that most genetic traits are not simply controlled by a single set of alleles.
Often many alleles, each with their own dominance relationships, contribute in varying ways to
complex traits. Some medical conditions may have multiple inheritance patterns, such as in
centronuclear myopathy or myotubular myopathy, where the autosomal dominant form is on
chromosome 19 but the sex-linked form is on the X chromosome.
Punnett Squares
The Punnett square is a diagram designed by Reginald Punnett and used by biologists to
determine the probability of an offspring having a particular genotype. It is made by comparing
all the possible combinations of alleles from the mother with those from the father.
21
Typical monohybrid cross
The Punnett square, founded by George Punnett, shows every possible combination when
combining one maternal allele with one paternal allele. In this example, both organisms have the
genotype Bb. They can produce gametes that contain either the B or b alleles. The probability of
an individual offspring having the genotype BB is 25%, Bb is 50%, and bb is 25%.
It is important to note that Punnett squares only
give probabilities for genotypes, not phenotypes.
The way in which the B and b alleles interact
B
Paternal
with each other to affect the appearance of the
b
offspring depends on how the gene products
(proteins) interact (see Mendelian inheritance). For classical dominant/recessive genes, like that
which determines whether a rat has black hair (B) or white hair (b), the dominant allele will
mask the recessive one. Thus in the example above 75% of the offspring will be black (BB or
Bb) while only 25% will be white (bb). The ratio of the phenotypes is 3:1, typical for a
monohybrid cross.
Maternal
B
b
BB
Bb
Bb
bb
Typical dihybrid cross
More complicated crosses can be made by looking at two or more genes. The Punnett square
only works, however, if the genes are independent of each other, which means that having a
particular allele of gene X does not imply having a particular allele of gene Y.
The following example illustrates a dihybrid cross between two heterozygous pea plants. R
represents the dominant allele for shape (round), while r represents the recessive allele
(wrinkled). Y represents the dominant allele for color (yellow), while y represents the recessive
allele (green). Each plant has the genotype Rr Yy, and since the alleles for shape and color genes
are independent, they can produce four types of gametes with all possible combinations: RY, Ry,
rY and ry.
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
Since dominant traits mask recessive traits,
there are nine combinations that have the
phenotype round yellow, three that are round
green, three that are wrinkled yellow and one
that is wrinkled green. The ratio 9:3:3:1 is
typical for a dihybrid cross.
Situations where Punnett squares do not apply
The phenotypic ratios of 3:1 and 9:3:3:1 are theoretical predictions based on the assumptions of
segregation and independent assortment of alleles (see Mendelian inheritance). Deviations from
the expected ratios can occur if any of the following conditions exists:
 the alleles in question are physically linked on the same chromosome
 one parent lacks a copy of the gene, e.g. human males have only one X chromosome,
from their mother, so only the maternal alleles have an effect on the organism (see sex
linkage)
 the survival rate of different genotypes is not the same, e.g. one combination of alleles
may be lethal so that the affected offspring dies in utero
22




alleles may show incomplete dominance or co-dominance (see dominance relationship)
there are genetic interactions (epistasis) between alleles of different genes
the trait is inherited on genetic material from only one parent, e.g. mitochondrial DNA is
only inherited from the mother (see maternal effect)
the alleles are imprinted
An example of a Trihybrid Cross is located at the end of this document.
Directions:
Please note: These are probabilities, and the actual results, as we all know, will vary. In
addition, the text is written as if it is fact rather than probability. Be sure to clarify that
individual results vary, like the coin flipping.
 Give each pair of students 128 red poker chips, 128 blue poker chips, 128 yellow poker
chips, one 4x4, 8x8 Punnett squares and a chess board.
 One student will be the paternal alleles and the partner will be the maternal alleles.
 Each gene is a single color. On one side of the poker chip is a large black dot. This
represents the upper case letter (dominant) state. The other side of the chip does not have
the dot. This side represents the lower case letter (recessive) state.
 Begin with a brief introduction to Mendel and his peas. He started with homozygous
parents.
 Tell your students to use the 4x4 square. Instruct them to complete the Punnett square
with one partner acting with only the dominant allele, and the other partner acting with
only the recessive allele. For our example here, let’s use the nose color (, NN and nn ) of
our Marshmallow bugs.
 What is the phenotype for each of the offspring? (They will all be heterozygous and
green noses).
 Using the same 4x4 square, repeat this with the heterozygote parents.
 What is the phenotype for each of the offspring? (They wil be 1 homozygote dominant, 1
homozygote recessive, and 2 heterozygotes, or 3 green and 1 yellow noses).
 Using the same 4x4 square, repeat with one parent homozygote recessive and one
heterozygote for this same gene.
 What is the phenotype for each of the offspring? (They will be 2 heterozygote and 2
homozygote recessive, or two green and two yellow noses).
 Introduce analyzing 2 genes, this time number of legs (L or l) and color of legs (R or r)
using the 8x8 squares.
 What is the phenotype for each of the offspring? (9, 3, 3, 1).
 Repeat with one parent homozygous recessive and the other parent is heterozygote. How
do the phenotype results change?
 Using the genes number of marshmallow spots (co-dominant S or s) and number of eyes
(incomplete dominance), what is the probability of the offspring phenotype?
 Introduce analyzing 3 genes, this time with number of antenna (A or a), number of body
segments (B or b) and color of antenna (T or t). Have the students predict if the results
will be different because these genes are found on two different chromosomes.
 What is the phenotype for each of the offspring (27, 9, 9, 9, 3, 3, 3, 1).
 For advanced students, have them calculate the probability of the phenotypes for 4 genes.
23
Trihybrid Cross
ABD
ABd
AbD
Abd
aBD
aBd
abD
abd
ABD
AABBDD
AABBDd
AABbDD
AABbDd
AaBBDD
AaBBDd
AaBbDD
AaBbDd
ABd
AABBDd
AABBdd
AABbDd
AABbdd
AaBBDd
AaBBdd
AaBbDd
AaBbdd
AbD
AABbDD
AABbDd
AAbbDD
AAbbDd
AaBbDD
AaBbDd
AabbDD
AabbDd
Abd
AABbDd
AABbdd
AAbbDd
A A bbdd
AaBbDd
AaBbdd
AabbDd
A a bbdd
aBD
AaBBDD
AaBBDd
AaBbDD
AaBbDd
aaBBDD
aaBBDd
aaBbDD
AaBbDd
aBd
AaBBDd
AaBBdd
AaBbDd
AaBbdd
aaBBDd
aaBBdd
aaBbDd
aaBbdd
abD
AaBbDD
AaBbDd
AabbDD
AabbDd
aaBbDD
aaBbDd
aabbDD
aabbDd
abd
AaBbDd
AaBbdd
AabbDd
A a bbdd
aaBbDd
aaBbdd
aabbDd
aabbdd
3
3
1
Phenotypic Ratio
27
9
9
9
3
24