1. Certain acquired characteristics, such as
mechanical or mathematical skill may be inherited.
2. Certain thoughts or experiences of a mother
mark or alter the hereditary makeup of an unborn
3. Color blindness is more common in males than in
4. A person may transmit characteristics to offspring
which he/she does not show.
5. Certain inherited traits may be altered by the
stars, planets or moon early in development.
6. The total number of male births exceeds female
births each year.
To distinguish between
heredity and inheritance
To describe Mendel’s
experiments in heredity
dominant vs. recessive.
Chapter 10.2, 10.3, 11.1, and
1866- Gregor Mendel
•Worked with Pea Plants
•Discovered how traits were inherited in a
Heredity – transmission of
traits from parents to their
used pea plants
Pollination – transfer of pollen from
anthers to stigma in flowers
1) self pollination
occurs within the
same flower or
2) cross pollination
Mendel’s Crosses with Pea Plants
All Tall plants
787 tall plants, 277 short plants
3 to 1 ratio
Genetics – study of heredity
Gene – segment of DNA on a
chromosome that codes for a
Allele – alternative form of a gene
T = tall
t = short
G = green
g = yellow
of an organism
(Ex: Blue eyes or Brown Eyes)
Genotype – genetic makeup
of an organism (genes)
Ex: BB, Bb, bb)
Where do Phenotypes come from?
Example of Genotype and
Homozygous – when both alleles
of a pair are the
Heterozygous – when both alleles
of a pair are not
In rabbits, black fur color is
dominant over brown fur color
B = black fur
b = brown fur
BB or Bb
Think – Pair - Share
If Fred Flintstone is heterozygous for black hair.
What is Fred’s genotype?
What is Fred’s phenotype?
Tweety bird is YY. (Y= yellow feathers, y=brown
1. What is his genotype?
2. What is his phenotype?
3. Is he heterozygous or homozygous? Explain.
dominant and recessive.
Due Tomorrow (or next time I see
Provide an example of the
To describe Mendel’s 3 laws
Complete a Monohybrid
**Take Out your Homework!!!
1) Law of Dominance
Each trait is controlled by 2
factors, one factor (dominant ) may
mask the other factor (recessive )
preventing it from having an effect.
2) Law of Segregation
Each allele a
Ex. Ww – one W
goes in one sperm
and the other w
goes into another
3) Law of Independent
R= Can roll your tongue
r= Can’t roll your tongue
Genotypic vs. Phenotypic
Ratio of different physical traits
Ex) Brown eyes ¼ or 25%
Ratio of the different possible alleles
Ex) Tt = ¼ or 25%
Test cross – an individual with
unknown genotype is crossed
with a homozygous recessive
used to determine
the genotype of
Lets Try a Test Cross
Spongebob squarepants doesn’t know
whether or not he is Homozygous
Dominant or Heterozygous for his yellow
color. The recessive trait is a white
sponge. Let’s say that we perform a “test
cross” on spongebob (spongebob + a
white female sponge) and all of the baby
sponges are yellow. What would
spongebob’s genotype be?
Lets Try a Monohybrid together!
1) Daffy Duck is heterozygous for black feathers.
Daisy Duck is homozygous for yellow feathers. Set
up a punnett square and determine probabilities of
their potential offspring. (Both genotype and
2) B = Black
b = yellow
Get with a partner and work on the
Sleeping Beauty has freckles. Her
prince charming is heterozygous
for no freckles. What are the
chances of her children having
freckles? Please show your work.
To set up and complete a
What is a dihybrid Cross?
A dihybrid cross allows us to predict
possible outcomes of offspring that will
have 2 traits simultaneously.
Ex: what would you get if you crossed a
Brown-haired brown-eyed male with a blondehaired blue-eyed female? How many of the
children would have brown hair and brown
eyes? Brown hair and blue eyes? Blonde hair
and brown eyes? Blonde hair and blue eyes?
Setting up Dihybrid Crosses
1. Determine parent genotypes
2. Determine alleles to be passed down
The FOIL method
3. Set up punnet square
4. Determine outcome
Looking at two different traits
Ex. Hair color and eye color
Mother is heterozygous for both traits
Father is heterozygous for eye color and homozygous
dominant for hair color
What could the phenotypes and
genotypes be of their children?
Mickey Mouse is heterozygous for Round
ears and homozygous for Black eyes.
Minnie Mouse also is homozygous for
Floppy ears and heterozygous for Black
eyes. Determine genotype and phenotype
ratios. (B=black, b=brown, R=round, r=
It’s Harry Potter time!! Get with a partner
and work on the sample problems
involving some of my favorite fictional
Take out your Harry Potter Homework!
What is the phenotypic ratio for a dihybrid
cross where each parent is heterozygous
for both traits?
To define gene
pedigrees and figure
out how to use one.
10.3 Gene Linkage and
Several genes on a chromosome
When two genes are close to each other on
the same chromosome
Linked genes on a chromosome results in
an exception to Mendel’s law of
Linked genes usually do not segregate
Drosophila (Fruit Flies)
First organism with linked genes
Linked genes typically travel together
during crossing over
Crossing over occurs more frequently
between genes that are far apart
Map of genes on a chromosomes and
frequency of crossing over
Occurrence of one or more extra sets of
all chromosomes in an organism.
Ex. A triploid organism (3n) - means that
it has three complete sets of
True or False – Correct false
_______ 1. Crossing over occurs more frequently
between genes that are close together on a
_______ 2. Gene linkage was first studied by
using garden peas.
_______ 3. Scientists call a drawing like the one
shown below a chromosome map.
_______ 4. Chromosome map percentages
represent actual chromosome distances.
Shows history of a trait in a family
Allows researchers to analyze traits within
Symbols for Pedigree
Lets try to figure out their
Dominant or Recessive
Pedigrees can depict both dominant and
Pedigree worksheet! Due next class! –
worth 5 points!!
Take out pedigree homework!
Fill in the genotypes for the following
b = blue eyes
Ariel and Prince Eric are curious to see
what their babies will look like! Eric is
heterozygous for black hair and Ariel has
the recessive trait of red hair. Both are
recessive for blue eyes. If they have 32
children, how many can we EXPECT to
have red hair and blue eyes?
To understand incomplete dominance and
be able to do incomplete dominance
To explain codominance, multiple alleles,
sex-linked traits, and polygenic
When the genotype of an individual is
unknown, cross the individual with a
The outcome of the cross determines the
genotype of the unknown
11.2 Incomplete Dominance:
Heterozygous phenotype is an
intermediate phenotype between the two
Two alleles are blended
Ex) Four O’clock Flowers
Red + White = Pink
Neither trait is dominant instead, both
traits are shown (No Blending)
Ex) Roan Cows
Red + White = RED AND WHITE
Sickle Cell Disease
Affects red blood cells and ability to
Homozygous recessive alleles=
Homozygous dominant alleles=
Sickle Cell and Malaria
People who are
heterozygous for sickle
cell, have a higher
resistance to malaria.
Multiple alleles – 3 or more alleles
that control a trait
Example – blood type (IA,IB,io)
Determine the possible offspring of the
1. AB and O
2. AA and BO
3. AB and AB
Coat Color of Rabbits
Rabbits have a hierarchy of coat color
4 alleles (C, cch, ch, and c)
Dominant C > cch> ch > c
C Full color
Coat Color of Rabbits
Let’s try a sample problem
cc x Ccch
Genotype and phenotype ratios
What do you see?
What do you see?
Sex Linked Traits
Traits located on the sex chromosomes
(X or Y)
X linked: gene is located on the X
Y linked: gene is located on the Y
What are the chances of having a
How would you go about solving it?
A man who is color blind marries a woman
that is heterozygous for color blindness.
What is the chance of having a color blind
Polygenic traits arise from the interaction
of multiple pairs of genes.
To define test cross
To define incomplete
To define codominance
Codominance – condition in which
both alleles of a gene are expressed
example – roan coat in horses
white hair (HW) is codominant with red
horses with genotype (HRHW) have
coats with a mixture of red and white
To predict the results of
dihybrid crosses by using
a Punnett square
dihybrid cross – cross between
individuals that involves two pair of