The Life & Times of Gregor Mendel
6 facts about Mendel’s life:
When was he born:
Where did he live:
What did his parents do for a living?
Where did Mendel go to school?
What did Mendel become?
What field did he study?
What nickname was he later given?
What plant did he study?
4 Reasons why he chose this plant to study:
1. _____________________________
3. _____________________________
2. _____________________________
4. _____________________________
Mendel’s Experiment:
First some basic flower knowledge:
Pea plants have both reproductive parts. They have carpels (__________________
part) and anthers (________________ part). Mendel knew this so sometimes he would let
plants self-fertilize, which means pollen from its own anther would pollinate its own plant’s
carpel.
If he wanted to cross two different plants, he would remove the plant’s
__________________. This way the plant couldn’t pollinate itself and he could control
breeding more easily.
The 1st Experiment
To start with, Mendel noticed that pea plants obtained only one of two colours;
_____________________ or ________________________. He wanted to figure out
how some plants obtained one colour over the other, so he started to breed his own pea
plants.
He saw that a white flower that self-fertilized will always have _____________
flowered offspring but with purple plants it was sometimes different. Sometimes a purple
plant that self-fertilized had all purple flowers but then other times it would also have some
white flowered offspring. He followed these steps to try to figure out why this happened:
Step 1: True breeding
He started by making sure he had True Breeding plants. A true breeding plant is…
_____________________________________________________________________
_________________________________________________________________.
Step 2: Hybridization
He took two true breeding plants of opposite colours and crossed them. He called these true
breeding parent plants the “parent” generation or the “P” generation. When he did this, he
found out that all the offspring were purple. He called these purple offspring the
_________ generation.
Step 3: Monohybrid Cross
He then allowed the F1 generation to self-pollinate. When he did this, he noticed that
there was always the same ratio of purple to white offspring. There was always a 3:1 ratio in
the F2 generation; 3 purple offspring for every white offspring.
How can we explain what happened to Mendel’s peas?
Mendel explained this first experiment using 2 Laws.
To explain why all the F1 generation was purple he came up with…
The Law of Dominance:
.
To explain why the white flowered plant came back in the F2 generation he came up with…
The Law of Segregation:
.
Additional Vocabulary:
Gamete:
.
Zygote:
.
Hybridization:
.
Test Cross:
.
Single Trait Inheritance: Sample Problems
1. A heterozygous purple plant is crossed with another heterozygous purple plant. What
is the genotypic and phenotypic ratio of their offspring?
2. A white pea plant is crossed with a heterozygous purple plant. What is the probability
of having a purple offspring?
3. In humans Widow’s peaks are dominant over flat hairlines. If two people with Widow’s
peaks have children 2 children with a flat hairline and 1 child with a widow’s peak, what
are the parents’ genotypes? Show your work using a punnett square.
The 2nd Experiment
After Mendel finished his monohybrid cross, he started to wonder whether or not
some of the traits might be linked to each other or whether traits were inherited
independent from one another. For example, he wondered whether the inheritance of
different pea shapes was dependent on other traits like, say…the colour of the peas inside
the pods. So he conducted an experiment that was very similar to his first one looking at
single trait inheritance, only this time he looked at two traits at once.
Step 1: Determine True breeding
Make sure the plant is true breeding for both traits.
Ex. Pea plants can have round peas or wrinkled peas. They can also have either yellow seeds
or green seeds. He made sure that one plant was true breeding Round and green and the
other was wrinkled and yellow.
Step 2: Hybridization
Crossed a true breeding round and green plant with a wrinkled and yellow plant and
found that all of the offspring were Round and yellow.
Step 3: Dihybrid cross
He allowed the F1 plants to self-fertilize and found that there was a 9:3:3:1 ratio in
the offspring (F2). There were 9 Yellow Round, 3 Round & green, 3 wrinkled & Yellow, and 1
wrinkled & green plant.
What was the answer to his question? Are different traits dependent or independent from
each other? Explain why you think so.
Mendel came up with his final law to explain whether genes were linked or not.
The law of Independent Assortment:
.
B12-1-01 Outline Gregor Mendel’s principles of inheritance, stating their importance to the understanding of
heredity (GLOs: A1, A2, B1, D1). Include: principles of segregation, dominance, and independent assortment.
Exceptions to Mendel’s Laws

Mendel studied inheritance in the 1800’s and therefore there was a lot of information
that he was missing

Little was known about ________________ and chromosomes and until Mendel, these
things were not scientifically understood

As more studies occurred, scientists realized that though Mendel had laid a good
foundation to the understanding of inheritance, there were still many
___________________________ to Mendel’s principles

It was lucky that Mendel had chosen peas to study inheritance because of the
__________________ nature of inheritance found within these plants

As more complex organisms were studied many _____________________ to his laws
became evident
Exceptions to Law of ___________________________

Mendel originally stated that there are ___________ factors for each gene and one
factor can be ______________________ over the other
o This was true for inheritance in pea plants, however there are two modes of
inheritance that are different than this

These methods are:
o __________________________ Dominance

When two alleles are ______________________ dominant

When the two different alleles combine they interact to produce a
_____________________________________

For example if a red and white individual cross they produce a
__________________ individual
o Co-Dominance

This is another type of incomplete dominance

The difference is that in this case _________________________ are
expressed at the same time

Ex) White cow (HwHw) X Red bull (HrHr)

Will have offspring with both hair colors (roan)
Practise Problem:
1. In snap dragons there are white and red flowers. When a white and a red flower have
children all offspring are pink.
a. What kind of inheritance is this? Explain.
White snapdragon crossed with a red Snapdragon
CwCw X CrCr
Complete the punnett square:
b. What would the F2 be if the F1 self-pollinate?
2. In cows a white cow and a red cow mate and have a calf with both white and red hairs
(roan)
a. What type of inheritance is this?
b. If this calf mates with another roan cow what will the phenotypes of their
children be?
Exceptions to the Law of Segregation
Multiple Alleles

The law of segregation states that there are __________ factors for every trait
(gene)

There are some genes that are more complex than this and may have more than 2
possible alleles

For example in humans there are ______________ different possible blood types
o Type _______________________________
o There are _____________ alleles that determine the type of blood that an
individual will have
o There are two dominant alleles, A and B

These are co-dominant (neither is more dominant than the other)

When both A and B alleles are present they create the blood type AB
o There is one recessive allele, O

When neither A or B are present the individual receives type _____
o The 3 possible alleles for blood type are:

________, _______, & _________

The genotypes for the different blood types are:
Blood type A=______________________
Blood type B=______________________
Blood Type AB= ____________________
Blood type O=______________________
Practise Problems
1. A man with type O blood marries a woman with type AB blood. What will be the
possible genotypes and phenotypes of their children? Show the punnett square for
this cross.
2. If a baby with blood type B is produced from a mother of type A, could a type O man
have fathered this child?
Lethal Genes

In 1905 Lucien Cuenot was studying inheritance of a coat colour gene in mice
o He crossed two heterozygous yellow mice

He never got the 3:1 ratio he should have

Instead he received a 2:1 ratio
o He determined that yellow was the __________________ allele
o He did test crosses to show that all the yellow individuals were
_____________________________

Later studies learned that homozygous yellow individuals experienced errors during
___________________________ development causing death
o This resulted in the unusual 2:1 ratio

In this experiment the lethal gene was in the form of a dominant allele, however,
they may also appear in __________________ alleles
Exceptions to the Law of Independent Assortment

This law states that each pair of alleles segregates _______________________ of
other pairs of alleles during gamete formation

There are two types of inheritance where this is not the case; ________________
genes & _______________________Traits

Linkage
o Linked genes are genes which are located on the ____________ chromosome

Genes (and alleles) are found in long sequences along a chromosome

The area a gene is found on a chromosome is called its ____________
o Linked genes don’t segregate independently but are often inherited together

They transmit together (ie. Red hair & Freckles/ Fair skin/freckles)
o New combinations do occur through crossing over that occurs when
chromosomes pair in meiosis (however this is more likely between genes found at
____________________ distances from each other on the chromosome)
o This means that a single chromosome can change as they pass from gen. to gen.
but often genes found closer to each other are inherited together

Polygenic traits
o Mendel studied traits controlled by 1 gene however some genes influence the
display of the ______________________ of other genes
o Polygenic Traits- traits that are affected by _____________than one gene
 Ex. Skin colour, eye colour, _______________, weight, metabolic rate
o Some traits are controlled by more than one gene
o Characteristics are determined by several pairs of independent genes

What’s the difference between polygenic traits and multiple alleles?
o Multiple allele inheritance shows many forms of a trait (there are more than 2
_________________)
o Polygenic inheritance is when genes interfere with the expression of each other
and show a __________________of traits.
Sex Determination & Sex Linked Inheritance

Thomas Hunt Morgan (1866-1945) conducted experiments on fruit flies (drosophila
malanogaster)
o Wanted to study Mendel’s principles
o Led him to discover sex chromosomes and linkage of traits

We have ______ chromosomes
o _______ pairs of chromosomes
o 1 pair of these chromosomes are ________________________________

Determines the sex of a child
o 22 of these 23 are ___________________________ chromosomes
(autosomes are __________ chromosomes other than the sex chromosomes)

There are two different sex chromosomes ( ____ & ____ chromosomes)
o Females have two X chromosomes (XX)
o Males have one X and one Y chromosome (XY)

The X chromosome carries more _________________ than just sex determination
o They carry anywhere between 100-200 other genetic traits

The Y chromosome is much smaller and only contains information related to
_______________________________________________
o It carries the SRY gene which carries information that creates maleness
Sex Linked Traits

Sex-linked traits are those traits whose genes are found on the ______
chromosome but not on the Y chromosome

Females would have 2 alleles for genes that are located on the X chromosome
o Females are XX (so one allele would be on each X chromosome)
o Females are more likely to show the ______________________ forms of
genes because they have two alleles for the genes

They are able to be HH, Hh, or hh which means there is a greater
chance of females having a dominant allele

Males are more susceptible to receiving recessive forms of genes because they only
have _________________________ for genes on the X chromosome because the
gene may not be located on the Y chromosome (therefore they have a 50% chance)

In humans, different sex-linked genes may have a defective recessive allele that
causes a disease
o Examples include: Hemophilia (blood cannot clot), colour blindness, sickle cell
anemia

Lethal recessive traits- sex-linked recessive traits that cause lethal
diseases/conditions (Duchenne muscular dystrophy)
Example Problem:
A man with hemophilia marries a homozygous normal woman. Predict the genotypes and
phenotypes of their children.
Step 1: track alleles
Step 2: record the chromosomes of each parent & then determine genotypes of parents
Dad: ______________
Mom: ________________
Step 3: set up a punnett square and combine gametes
Step 4: State genoytpic and phenotypic ratio of the F1 generation
Sample Problems:
1. A man who is colourblind marries a woman who is homozygous dominant for
colourblindness. What is the probability that they will have children who are carriers
of colourblindness?
2. A man who does not have hemophilia marries a woman who is a carrier for hemophilia.
What is the probability that they will have a boy? If their child is a boy what is the
probability that he will have hemophilia?
3. A man who is colourblind marries a woman whose father was colourblind.
a. What are the genotypes of the parents?
b. What is the probability of their children being colourblind.
Pedigree Charts





A pedigree chart is a graphic representation of inheritance
It is an organized method of recording the history of a certain trait or condition throughout a family
o Essentially it is a family tree displaying the inheritance of a specific trait
Pedigree charts show only the phenotype of a specific trait (they do not display genotypes)
o Estimating genotypes is possible by observing a pedigree chart
Pedigree charts specific symbols to represent different types of individuals and relationships
The symbols used in pedigree charts include the following:
= ________________________________
= ________________________________
= individuals _________________________ a trait/condition
= ________________________________
= offspring in birth order


(I & II represent ___________________________________)
(individuals are always placed from left to right according to
__________________________________)
Inheritance Pattern #1:
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
_______________________________________
Inheritance Pattern #2:
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
_______________________________________
Inheritance Pattern #3:
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
_______________________________________
Sample problem:
Jean is given a homework assignment to track the inheritance of attached earlobes through her family
extending all the way to her grandparents. She decides to create a pedigree chart representing the
inheritance of this trait. She does some investigating through old photographs and discovers the following
the following information. Jean is the youngest member of her family and she along with one of her
brothers (21) both have attached earlobes. Her other brother’s ears (16) are not attached. Neither of her
parents have attached ear lobes. Her dad is the oldest member of his family. His younger sister has
attached earlobes (42) but his youngest sister does not (40). His dad does not have attached earlobes but
his Grandmother does.
Questions: Draw a pedigree chart representing this. Explain what type of inheritance this is. List the genotypes for each
individual.