Goal #2: Punnett Squares

C. Mendel’s Principle of
1. Dominance: form
of a trait that
masks another
form of a trait –P
2. Recessive: form
of a trait that is
masked - p
III. Probability:
science that helps
determine the
chance that
something will take
a. multiple trials
provide more
accurate results.
b. Scientific
research is based on
accurate, repeatable
Goal #2: Punnett Squares
IV. Punnett square:
A diagram that
shows how alleles
of a gene from
two parents
combine to form
– used to predict
results of
A. Dominant allele
1. Use a capital
2. Ex: B= Brown eyes
B. Recessive allele
1. Use lower case
2. Ex: b= blue eyes
When an individual has different amounts
of melanin in each of their irises, their
eyes are different colors. Heterochromia
iridium (the scientific name for two
different color eyes in the same
individual) is relatively rare in humans but
common in some animals, such as
horses, cats, and certain species of
dogs. A variation on the condition is
heterochromia iridis, in which an
individual has a variety of colors within
one iris.
Heterochromia iridium is thought to result
from an alteration to one of the genes
that controls eye color. This can be an
inherited trait, although trauma and
certain medications may result in
increased or decreased pigmentation in
one of the irises. Certain medical
syndromes, such as Waardenburg
syndrome, may also cause someone to
have two different colored eyes.
C. Genotype: genetic make-up of an organism
1. cells have at least 2 alleles for every trait
2. Homozygous- organism with two alleles for
a characteristic that are the same - purebreds
- can be dominant (TT) or recessive (tt)
3. Heterozygous- organism with two different
alleles for a characteristic (Tt)
– hybrids
D. Phenotype:
physical appearance
of the trait shown
by the particular
– Qualitative
– Ex: tall plant,
blue eyes, blond
hair, etc.
V. Law of
Segregation pairs of alleles
separate, or
segregate, during
meiosis (the
formation of
• means that a
gamete only
receives one half
of the pair of
alleles of one gene
VI. Constructing Monohybrid Crosses
• 3 types
1. Homozygous x Homozygous
(AA x AA, AA x aa, or aa x aa)
2. Heterozygous x Homozygous
(Aa x AA or Aa x aa)
3. Heterozygous x Heterozygous
(Aa x Aa)
Genetics problem:
Black is the dominant allele of
the trait for color of hair on
Labrador retrievers. Yellow is
the recessive allele. If a
purebred black lab is bred
with a purebred yellow lab,
what will the genotypes and
phenotypes of the 1st
generation of offspring be?
Problem Set-up:
B= Black
b= Yellow
P1: BB x bb
F1 Genotype:
F1 Phenotype:
F1 ratio:
Now set up a cross (using the correct setup) in your notes crossing the F1 and
record the results of the F2 genotypes
and phenotypes.
• Trade with partner next to you and
• Ask questions if you are unsure 
• You will have to do this on the test!
VII. Testcrosses crossing an unknown
individual with a
recessive individual
to find the unknown.
A. This is a little
like “guess and
check” in math
Short hair is dominant over long hair in
monkeys. Cross a homozygous short hair
monkey with a heterozygous monkey.
B#1: How are dimples inherited?
C#2: Punnett Squares
Construct a manual on how to use Punnett squares. Include a
labeled diagram of a Punnett square, step-by-step directions on how
to use one, why they are so useful in genetics, and an example of
Imagine you came upon a tall pea plant similar to those Mendel used
in his experiments. How could you determine the plant’s genotype
with respect to height? Draw 2 Punnett squares to show your answer.
Complete worksheets “Bikini Bottom Genetics” & “Bikini Bottom
Genetics 2” – available on my website. Each worksheet worth 5
11-2 Section Assessment – must be in complete sentences

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