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Intro to Genetics
Genetics
Student Expectation:
B 6.F
Predict possible outcomes of various
genetic combinations such as
monohybrid crosses, dihybrid crosses
and non-Mendelian inheritance.
Readiness Standard
Gregor Mendel
Austrian monk born 1822
 Lived in a monastery
and taught high school
 Experimented with pea plants by cross
breeding plants with different
characteristics and studying results.
 Known as the father of Genetics

Mendel’s Principles
Law of Inheritance – Characteristics or
traits are inherited by individual units
known as “genes”.
Vocabulary

Gene – the sequence of DNA that codes
for a protein and thus determines a trait.

Example – a gene
will determine plant
height in peas.
Mendel’s Principles

Law of Segregation - states that during
the formation of reproductive cells
(gametes), pairs of hereditary factors
(genes) for a specific trait separate so
that offspring receive one factor from
each parent.
Vocabulary

Allele – one of a number of different
forms of a gene.

Example:
this flower
carries an
allele for white
and an allele for purple flowers
Mendel’s Principles
Law of Independent
Assortment - states
that chance determines which factor
for a particular trait
is inherited.
Mendel’s Principles

Law of Dominance – states that when 2
or more forms of a gene exist (alleles),
some forms are dominant and others are
recessive
Dominant/Recessive
Hitch Hikers Thumb
Normal Thumb
Dominant/Recessive
Free Earlobes
Attached Earlobes
Dominant/Recessive
Polydactyly is Dominant!!
Dominant/Recessive
Other examples of dominant traits:
Dimples
Tongue Rolling
Freckles
Curly hair (may be more than one gene)
Dominant/Recessive
Shapes for Pea seeds
R = round (Dominant)
r = wrinkled (recessive)
Genotype
RR
Rr
rr
Phenotype
Round
homozygous dominant
Round
heterozygous dominant
wrinkled
homozygous recessive
Monohybrid Crosses
Monohybrid Crosses
Monohybrid Crosses

Practice some monohybrid crosses
BB x BB
BB x Bb
BB x bb
Bb x Bb
Bb x bb
What are the genotypic ratios?
What are the phenotypic ratios?
Dihybrid Crosses
Non Mendelian Genetics
Exceptions to Mendel’s Principles:
- Not all genes show simple patterns of
dominant and recessive alleles
- The majority of genes have more than
two alleles.
- Many traits are controlled by more than
one gene.
Non Mendelian Genetics
Incomplete Dominance - When one
allele is not dominant over the other but
the heterozygous offspring produce an
intermediate (3rd) phenotype. Neither
fully expressed.
 Example:
Red (RR) x white (rr)
= Pink (Rr)

Non Mendelian Genetics


Co-dominance - Both alleles contribute to the
phenotype. Both are expressed at the same
time.
Example:
Brown BB x
White WW
= brown and white - BW
Non Mendelian Genetics

Multiple Alleles - More than 2 possible
alleles exist – not “either/or”. Only 2
Can Receive
expressed at a
Blood Type
Genotype
Blood From
time.
i i = AO
A
A

iAiA = AA
A or O
Example:
Blood Type
B
iBi = BO
iBiB = BB
B or O
AB
iAiB
A, B,
AB, O
iA, iB, iAiB, ii
O
ii = OO
O
Multiple Alleles – Blood Types
Non Mendelian Genetics

Polygenic Traits - Traits controlled by
several genes often on multiple
chromosomes.
Examples:
Skin Color
Eye Color

Polygenic
Traits
Skin Color
Non Mendelian Genetics
Sex Linked Traits Genes that are carried
by the sex chromosomes.

Read More:
http://anthro.palomar.edu/biobasis/bio_4.htm
Journal Work
In your journal you will work the following
punnett squares. This will be a graded
assignment.
 You must re-write or abbreviate the
questions and you must show your work
and circle or hi-lite your answers.

Journal Work Problem 1

Identify each of the following as:
Homozygous dominant, homozygous
recessive or heterozygous.
A.
B.
C.
D.
E.
bb
Hybrid
TT
Gg
Purebred
Journal Work - Problem 2
Dominant/Recessive Monohybrid Cross
Draw a Punnett square and provide the genotypic
and phenotypic information.
I = Not allergic to Iodine
i – allergic to iodine
Ii x II
Genotypic ratios
Phenotypic ratios
Ii x ii
Genotypic ratios
Phenotypic ratios
Journal Work - Problem 3
Dominant/Recessive Monohybrid Cross
Two elephants are crossed and the resulting
offspring have 50% large ears and 50% small
ears.
E = large ears e = small ears
What are the genotypes of the parent?
SHOW YOUR PUNNETT SQUARE.
Journal Work - Problem 4
Dominant/Recessive Monohybrid Cross
A black rabbit is crossed with a white rabbit.
100% of the offspring are heterozygous for
color.
B = black
b = white
What are the genotypes of the parent?
What are the phenotype percents for the offspring?
SHOW YOUR PUNNETT SQUARE.
Journal Work - Problem 5
Dominant/Recessive Monohybrid Cross
Cross a homozygous fuzzy bear with a
hairless bear.
F = fuzzy
f – hairless
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work - Problem 6
Dominant/Recessive Monohybrid Cross
Cross a heterozygous purple-flowered plant
with a plant that has white flowers.
P = purple
p – white
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work – Problem 7
Dominant/Recessive Dihybrid Cross:
Y – yellow peas
y – green peas
P – purple flowers
p – white flowers
T-tall plant
t – short plant
Cross two heterozygous tall, heterozygous
yellow pea plants.
What are the parent genotypes?
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work – Problem 8
Dominant/Recessive Dihybrid Cross:
Y – yellow peas
y – green peas
P – purple flowers
p – white flower
T-tall plant
t – short plant
Cross a short, purple flower plant that is
homozygous for color with a short, purple
flower plant that is heterozygous for color.
Whate are the parent genotypes?
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work – Problem 9
Dominant/Recessive Dihybrid Cross:
Y – yellow peas
y – green peas
P – purple flowers
p – white flower
T-tall plant
t – short plant
Cross a heterozygous purple flowered, green
pea plant with a plant that has white flowers
and is heterozygous for pea color.
What are the parent genotypes?
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work – Problem 10
Incomplete Dominance - Monohybrid Cross:
In snapdragons, red and white are both dominant.
When they cross, they produce a pink flower.
R – red
R’ – white
Cross a homozygous red and a homozygous white
snapdragon.
What are the parent genotypes?
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work – Problem 11
Co - Dominance - Monohybrid Cross:
In a certain type of chicken, black and white feather share
dominance. When they cross they produce chickens with
both black and white feathers.
B - black
B’ - white
Cross a homozygous black and a homozygous white chicken.
Whate are the parent genotypes?
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work – Problem 12
Incomplete and Co - Dominance - Dihybrid Cross:
In Fuzzy Trolls, Blue and Purple hair are both dominant. A
hybrid genotype produces blue and purple stripes. Yellow
skin and Red skin are both dominant. A hybrid genotype
produces orange skin.
B – Blue hair
B’ – Purple hair
Y – yellow skin
Y’ Red skin
A troll with purple hair and red skin reproduces with a troll
with blue hair and orange skin.
What are the parent genotypes?
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work – Problem 13
Multiple Alleles Monohybrid Cross:
Blood Type: Cross a
heterozygous Type A
with a heterozygous Type B.
Blood Type
Genotype
Can Receive
Blood From
A
iAi = AO
iAiA = AA
A or O
B
iBi = BO
iBiB = BB
B or O
AB
iAiB
A, B,
AB, O
O
ii = OO
O
Whate are the parent genotypes?
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
Journal Work – Problem 14
Sex Linked - Monohybrid Cross:
A female who is a carrier for baldness marries a
man with normal hair patterns
H – Normal hair pattern
What are the parent genotypes?
What are the F1 genotypic ratios?
What are the F1 phenotypic ratios?
h – bald