Lesson Plan: Traits and predicting genotypes and phenotypes
Analyze Learners: Overview & Purpose
 In this lesson students will learn how to predict the possible phenotypes and
genotypes so that they can calculate probabilities of inheriting specific traits
from parents.
o Predicting the outcome of a genetic cross is important because
predicting the possible outcomes of inheriting traits can be used to
help individuals, with history of genetic diseases and disorders in
family, determine whether to undergo particular genetic tests.
 STEM application, career connections, and/or societal impacts:
o Genetic testing, the math involved in probability, and new
technologies like gene therapy all are STEM applications.
o Career connections: genetic therapist, researcher to prevent
unfavorable traits (gene therapy), lawyer, forensics, biotechnology
industry (medicine, cancer treatment and research), selective
breeding in prized animals.
o Societal impacts: prevalence of some genetic disorders can be
researched through the use of phenotypes and genotypes.
Controversial topic: genetically engineered offspring? People who choose not to
have children due to “probability” they will produce offspring with disorders (down
syndrome, dwarfism, sickle cell anemia)
Standards: Local standards from Campbell County School District #1
SC-BI-03-06 - Analyze the Mechanics of Genetics (Objective)
S - Supporting
 Students will demonstrate how traits are inherited by using a monohybrid cross,
including parents genotype, all different sex cells, appropriate punnett square,
phenotypes and genotypes and both ratios of the F1. Describe mitosis, meiosis,
and DNA as it relates to heredity.
SC-BI-03-07 - Identify the Mechanics of Genetics (Objective)
S - Supporting
 Students will define the terms: genotype, phenotype, homozygous, heterozygous;
demonstrate the use of a punnett square in a mono and dihybrid cross, incomplete
dominance cross; discuss the role of heredity and environment; demonstrate how
the sex is determined genetically; discuss the causes of identical and fraternal
twins.
Misconceptions:
 Phenotype and genotype are interchangeable
 Genetic information or traits are inherited from the same-sex parent (i.e.
daughters get their mother's DNA and sons get their father's DNA)
Objectives:
SWBAT:
•Demonstrate use of Punnett Squares to predict genotypes and phenotypes.
•Compile probability and ratios for outcomes of Punnett Squares.
•Determine their possible genotypes of a specific phenotype they express.
Agenda:
•Traits lecture
•Learn how to use Punnett Squares
•Observe traits
Goals:
Promote mastery of simple and complex skills and knowledge surrounding
human heredity, genetics, punnett square equations and use. These skills and
declarative knowledge will be taught in a step-by-step fashion.
Cross-cutting concepts:
 Models and patternsmath, engineering, cells
 Structure and function
 Biotechnologyselective breeding in animals and plants…humans?
 Diversity – evolution, cultural studies, classification of species
 Probability – math, technology, evolution, gambling!
Safety:
No use of dangerous materials. Students instructed to follow general school safety
guidelines.

Unifying concepts:
 Evolution
 Math
Materials:
 Observing traits handout with chart
 Pencil
Pre-test: (2 min)
 What is probability?
 How can we use probability to predict traits?
HUMAN HEREDITY
What makes you who you are?
Heredity and Environment
1. Heredity –traits passed to you from your biological parents.
 Chromosome
 Gene
 Two types of traits:
 Species traits – genes carried by all normal members of species.
 Individual traits – makes an individual unique.
**Determines potential
2. Inherited characteristics are controlled by factors that occur in pairs.
Factors = GENES
 Each trait controlled by one gene pair that occurred in 2 contrasting
forms
o These different forms=alleles
o Allele – one of a number of different forms of a gene.
3. Principle of Dominance (and recessivness): this principle states that some
alleles are dominant and others are recessive.
a. Dominant – most powerful, important, or influential.
 One gene in pair may mask other (Ex: T-dominant trait masks
t-recessive trait)
b. Recessive – characteristic of an allele that is not expressed when a
dominant allele is present (in most cases).
 The recessive allele is expressed only when the dominant allele
is not present in genotype.
c. Hybrid – Tt (alleles are different)
 Dominant gene is expressed
a. Genes occur in pairs: one from male (dad) and one from female (mom)
various combinations possible…TT or Tt or tt from gametes.
*Gametes – sex cells, offspring made from the fertilization of the
female
gamete (egg cell) by the male gamete (sperm
cell).
**Gametes are haploid - term used to refer to a cell that contain on a
single set of genes.
b. Genotype – “gene type”- actual genes present in cell
-text definition: genetic makeup of an organism (Tt).
c. Phenotype – what you see; physical characteristics expressed in an
organism
 TT & Tt = are different genotypes but same phenotype
d. Homozygous – having two identical alleles for a particular gene.
 Ex) TT, tt, YY
e. Heterozygous – having two different alleles for a particular gene.
 Ex) Tt and Yy
with
i. How do we predict the outcome of various crosses.
a. Punnett squares – grid system that uses mathematical probability to
help predict the genotype and phenotype combinations in genetic
crosses.
 Show probability of each genotype
Example: TT (male) x tt (female) T=tall and t=short
T
T
t
Tt
Tt
t
Tt
Tt
*All offspring would be heterozygous tall (Tt)
Example: Tt (male) x Tt (female)
T
t
T
TT
Tt
t
Tt
tt

Probabilities:
 Phenotypic - 3:1 (3 tall =TT, Tt, Tt: 1 short=tt)
 Genotypic – 1:2:1 (1 TT: 2 Tt: 1 tt)
 ¾ = 75% tall and ¼ = 25% short
 75% chance offspring will be tall and 25% chance
offspring will be short
b. Monohybrid cross: cross of only one trait a “one factor cross”
(height).
c. Dihybrid cross: cross of two traits a “two factor cross” (height and
color).
Example) RRyy (male) x rrYY (female)
R=round, r=wrinkled, Y=yellow, y=green
rY
rY
rY
rY
Ry
RrYy
RrYy
RrYy
RrYy
Ry
RrYy
RrYy
RrYy
RrYy
Ry
RrYy
RrYy
RrYy
RrYy
Ry
RrYy
RrYy
RrYy
RrYy
*Phenotypic ratio = 16:0…100% of offspring are RrYy
*Genotypic ratio = 16:0…100% of offspring are RrYy
Mini-Activity: Observing Human Traits ~15 min
We will take about 5 minutes to observe some of our very own traits (tongue rolling,
earlobes, and dimples) that are determined by the expression of dominant and
recessive alleles. Some human traits are determined by three or more traits, complex
interactions among several genes, and environmental factors BUT in this activity we
will explore human traits that are determined by just two alleles – one recessive and
one dominant.
** The following information that is collected below will be written on the board as
well as the students will be given this chart to fill out:
Trait
Trait
# of Students # of students
demonstrating demonstrating
dominant
recessive trait
phenotype
%
demonstrating
dominant
phenotype
%
demonstrating
recessive
phenotype
Dominant
Recessive
Tongue
Roller (R)
Non-roller (r)
16
2
89%
11%
Free earlobes
(E)
Attached
earlobes (e)
17
1
94%
6%
Dimples (D)
No dimples
(d)
7
11
39%
61%
Right-handed
H)
Left-handed
(h)
Freckles (F)
No freckles
(f)
Widow’s
peak (W)
Straight
hairline (w)
Hitchhikers
thumb (K)
Straight
thumb (k)
Left over
right thumb
crossing (L)
Right over
left thumb
crossing (l)
1. Students will be asked to raise their hand if they indeed can roll their tongues.
We will count and record those that can and cannot roll their tongues. We will
continue this mini survey for free or attached earlobes as well as dimples and no
dimples.
2. Students may need to ask teacher or student if they in fact are rolling their tongue,
have dimples, or attached earlobes.
3. Collectively ask class what the %’s are for students demonstrating dominant and
recessive traits. Formula: #dominant  # students * 100% = % demonstrating
dominant.
#recessive  # students * 100% = % demonstrating
recessive.
4. Call on a student (popsicle sticks with names on them) and ask,
 “For each trait, which occurs more frequently: dominant or recessive
allele?”
 “Do dominant traits occur more often than recessive traits? Explain”
 “What would happen to your results if you were to perform this
investigation/survey with five other classes and recorded their data.
 “Using height as an example of a hereditary trait to explain how human
heredity is different from heredity in peas.”
5. After you have calculated the % of students demonstrating the dominant and
recessive traits you can EXTEND the activity by then proceeding your students
to:
a. Calculate probabilities of the above traits between two students and their
possible genotypes for the traits.
b. Ex: ‘Johnny’s’ Phenotype: dimples; possible genotypes are DD or Dd.
‘Sarah’s’ phenotype: no dimples; possible genotypes are dd.
DD x dd
d
d
D
D
Dd
Dd
Dd
Dd x dd
D
d
d
Dd
dd
d
Dd
dd
Dd
Probability that Johnny (DD) and Sarah (dd) will have children with dimples: 100%
Phenotype ratio = 4:0 all children would have dimples
Genotypes = 4:0 all children would be Dd
Probability that Johnny (Dd) and Sarah (dd) will have children with dimples: 50% &
50% will NOT have dimples.
Phenotype ratio = 2:2 (1:1) ½ the children would have dimples and ½ the
children would NOT have dimples (dd)
Genotypes = 2:2 ½ children would be Dd and ½ children would be dd.
***You can continue even further and cross 2 heterozygous parents***
Continue lecture using teachers notes below:
4. Environment – all external forces acting on an organism.
**Determines if potential will be reached
5. Studying Human Genetics:
 Population sampling (random/cross-section) ·sample size?
 Pedigree – family record →shows how trait is inherited over several
generations.
 Carrier – individual heterozygous for trait but doesn’t “show” trait.
 Twin Studies: study of identical twins
 Genetic vs. Environmental influences
6. Inheritance Patterns:



Gene linkage – genes on single chromosomes inherited together.
 Different chromosomes assort independently.
Crossing over – 2 homologous chromosomes side by side sections cross,
break off, and re-attach
 Form recombinants:
New combinations of alleles→increases genetic variety
Sex Linkage
a) Sex chromosomes – look mismatched
 Thomas Hunt Morgan and fruit flies
 Not homologous →one large one (or small in some
cases)
 X chromosome – large
 Y chromosome – small
i. Female = XX
ii. Male = XY
iii. All eggs from meiosis→X
iv. Sperm →50% X and 50% Y (males
determine sex of offspring)
Male=XY & Female = XX
X
X
X
XX
XX
Y
XY
XY
 Phenotypic ratio = 2:2 or 1:1
 Genotypic ratio = 2:2 or 1:1
 50% chance offspring will be male & 50% chance female
a) Autosomes – All other chromosomes
 Homologous
Review:
verbally review these terms and concepts:






Phenotype: physical trait of an organism (what we see).
Genotype: genetic makeup of an organism (Tt).
Punnett Squares: diagram that can be used to predict the genotype and
phenotype combinations of a genetic cross.
o Do one more punnett square with them, one from the activity possibly
Dominant: most powerful, important, and/or influential.
Recessive: characteristic of an allele that is not expressed when a dominant
allele is present (in most cases).
Traits – specific characteristic, such as seed color or plant height, of an
individual.
Complete more punnett squares and determine ratios and probabilities.
Post-test:
 What is probability?
 How can we use probability to predict traits?
Assessments:
Formative: during the “Observing Human Traits Lab” I will be checking for
understanding by assessing the participation and whether students are grasping
what I have taught them thus far.
Summative: Students will be asked to write down which parent they think
they got this trait from and then create a fake punnett square to determine how
they, hypothetically, got their trait from that parent. I may re-think this assessment
because some of my students do not have both parents in their lives and this could
be a touchy subject for some.
Questions:
Low:
 What is phenotype? Genotype?
Middle:
 Describe or draw and use a Punnett Square.
High:
 Suppose you are an avid gardener. One day, you come across a plant with
beautiful lavender flowers. Knowing that the plant is self-pollinating, you
harvest its seeds and plant them. Of the 106 plants that grow from these
seeds, 31 have white flowers. Using a punnett square, draw conclusions
about the nature of the allele for lavender flowers
Accommodations:
I have several students that either struggle with keeping up with me and my
outline/notes on the board as well as a student that just processes information
slower than most. For these students I will provide a copy of my outline/notes.
This will allow them to make their own notes in addition to the notes I provide them
and will hopefully help them follow because they will not become discouraged with
their poor writing skills.
Textbook’s glossary also has definitions in Spanish!