Chapter Introduction
Lesson 1 Mendel and His
Peas
Lesson 2 Understanding
Inheritance
Do you agree or disagree?
1. Like mixing paints, parents’ traits
always blend in their offspring.
2. If you look more like your mother than
you look like your father, then you
received more traits from your mother.
3. All inherited traits follow Mendel’s
patterns of inheritance.
Do you agree or disagree?
4. Scientists have tools to predict the form
of a trait an offspring might inherit.
5. Any condition present at birth is
genetic.
6. A change in the sequence of an
organism’s DNA always changes the
organism’s traits.
How are traits passed
from parents to
offspring?
GENETICS
What other words
begin with gen- ?
Student Traits
Earlobes
Thumbs
Tongue
Rolling
Mendel and His Peas
SWBAT
• Explain why Mendel performed crosspollination experiments
• Describe what Mendel concluded
about inherited traits
Some terms to know…
Gene- hereditary factors that determine your
traits (found in your DNA)
Traits- the way something looks or acts (color,
size ect)
Genotype: What genes you have TT
Phenotype: What your genes make you look
like TT = tall tt= short
Early Ideas About Heredity
*Heredity is the passing
of Genes (traits) from
parents to offspring.
*Gregor Mendel is known
as the father of
genetics—the study of
how Genes (traits) are
passed from parents to
offspring.
Gregor Mendel- The man who mathematically proved that “it” is
actually not in your blood
*Mendel studied genetics by doing controlled breeding
experiments with
pea plants.
Attention!
* Gregor did all of
his research before we
even knew about DNA!
Mendel’s Experimental Methods (cont.)
*When a homozygous (true-breeding
plant) PP self-pollinates, it always
produces offspring with traits that
match the parent.
(for example: white flowers that
always produce offspring that have
white flowers)
When Mendel crossed true-breeding or homozygous
plants they always gave offspring with the same
phenotypes
Mendel’s Results
* Once Mendel had enough homozygous (PP-
purple) and (pp- white) plants for a trait he
wanted to test, he cross-pollinated selected
plants.
* Plants are called hybrids or heterozygous
(Pp) if they come from homozygous parent
plants with different forms of the same
trait. – for example P-purple and p-white
Cross-Pollination
What is “odd” about the offspring
that were produced?
What do you think he did next?
Mendel’s Results (cont.)
hybrid
Science Use the offspring of two
animals or plants with different forms of
the same trait
Common Use having two types of
components that perform the same
function, such as a vehicle powered by
both a gas engine and an electric motor
Second-Generation (Hybrid) Crosses
Mendel’s Results
Mendel recorded
traits of offspring
from many hybrid
crosses.
Now it is time to
do some ratios!!!
Mendel’s Conclusions
Important! – Due to the Mathematical Ratios
Mendel concluded that two factors, one from
each sperm and one from each egg, control
each inherited trait.
A ratio of 3:1 is only seen if there are two
hybrid crosses with one of the two traits being
dominant!!!
Mendel’s Conclusions (cont.)
* A dominant trait is a genetic factor that
blocks another genetic factor.
* A recessive trait is a genetic factor that is
blocked by the presence of a dominant
factor.
*Review Questions
1. What is heredity?
2. What did Mendel conclude about sexually
reproducing organisms?
3. One of these factors comes from ________
and the other comes from ________.
4. Describe how a flower could be purple but
still have a gene for being white!
• Genetics is the study of how traits
are passed from parents to offspring.
• Mendel studied genetics by doing
cross-breeding
experiments with
pea plants.
• Mendel’s experiments with pea
plants showed that some traits are
dominant and others are recessive.
*Mendel Song
Mendel’s Conclusions (cont.)
How do dominant and
recessive factors interact?
What method did Mendel use to
select which plants pollinated
other plants?
A.
B.
C.
D.
true breeding
self-pollination
cross-pollination
bees
*Lesson 1
How many dominant factors does
a purple-flowering pea plant
have?
A.
B.
C.
D.
0
1
2
1 or 2
*Lesson 1
What is the approximate ratio of
dominant to recessive expression
when both parents are hybrid?
A.
B.
C.
D.
1
2
3
4
:
:
:
:
1
1
1
1
*Lesson 1
Do Now: Ratios
Understanding Inheritance
SWBAT
• State what determines the expression of traits
• Show how can inheritance be modeled
Review: What Controls Traits
*Mendel concluded that two factors—one from
each parent—control each trait.
*Mendel’s “factors” are part of chromosomes
which exist as pairs—one chromosome from
each parent.
*Each cell in an offspring organism contains
chromosomes from both parents.
What Controls Traits (cont.)
*A gene is a section on a chromosome that
has genetic information for one trait.
*The different forms of a gene are called
alleles. Each chromosome has one allele for
every gene on it.
*The two chromosomes
in an offspring cell may
have the same or
different alleles.
*Lesson 2
What Controls Traits (cont.)
*Geneticists call how a
trait appears, or is
expressed, the trait’s
phenotype.
• The two alleles that
control the phenotype of
a trait are called the
trait’s genotype.
What Controls Traits (cont.)
phenotype
from Greek phainein, means “to
show”
What Controls Traits (cont.)
* When the two alleles of a
gene are the same, the
genotype is homozygous.
• If the two alleles of a gene are
different, the genotype is
heterozygous.
What Controls Traits (cont.)
Scientists use uppercase and lowercase letters
as symbols to represent the alleles in a
genotype.
How do alleles determine the
expression of traits?
Modeling Inheritance
A Punnett square is a model used to predict possible
genotypes and phenotypes of offspring.
A pedigree shows phenotypes of genetically related
family members.
Male = square Female = circle
1. How many
generations are
represented in this
chart?
2. How many children
were there in the
second generation?
How many were
affected.
3. Is it possible for the
dad in G1 to be
homozygous dominant?
Why?
Complex Patterns of Inheritance
SWBAT
A- Differentiate between codominance and incomplete dominance
B- List several environmental factors that can affect gene
expression / phenotype
Codominance occurs when both alleles
can be observed in a phenotype.
*Sometimes traits appear to be blends of
alleles.
*Alleles show incomplete dominance when
the offspring’s phenotype is a blend of the
parents’ phenotypes.
Polygenic
inheritance occurs
when multiple genes
determine the
phenotype of a trait.
Genes and the Environment
* The environment can turn on or off
certain genes! This changes the
organism's phenotype.
* In all cases it usually helps the
organisms survive in its environment.
(if it didn't help the organism probably
already died)
Mutagens - environmental factors that causes a change in
a gene DNA sequence or affects the way a gene functions
“Natural” Factors
*The three common factors that
affect gene expression:
*Temperature
*Ph (Acidity or Basicity)
*Time of year
*Environment on Genes
*A Siamese cat produces
darker fur in cooler
areas of its body.
*The cold environment
activates the gene for
darker fur!
*Environment Affecting
Gene Expression
Some corn kernels turn bright red in the
presence of sunlight!!!
*Human Skin Color-Tanning
*UV light from the Sun
turns on the gene to
produce melanin
*This causes our skin to
get darker to protect
us from the Sun’s
harmful rays!
Click on rabbit for video
*Review Questions
1. Give and example that shows how the
environment can affect the phenotype of an
organism.
2. What environmental factors affect phenotype?
3. Does having a gene that predisposes a person to
a disease such as heart disease or diabetes mean
the person is destined to develop the disease?
Humans
*We know that cancer and heart disease “runs” in certain
families
*Does this mean that you will defiantly get the disease?-- Absolutely not!
*What you do with and put into your body will affect
what those genes do. That would be you body’s
environment.
*Ex: If cancer runs in your family and you chose to eat
healthy, use sun block, not smoke and exercise your
chances of getting it are very low! That is supplying
your body with the “Right Environment.”
• The genes for traits are located on
chromosomes.
• Geneticists use Punnett squares to
predict the possible genotypes and
phenotypes of offspring.
• In polygenic
inheritance, traits
are determined by
more than one
gene and have
many possible
phenotypes.
*Lesson 2
Genetics will now be broken up into
two smaller units
(everything before this is Gen1 and
everything after this is Gen2)
*Now complete your
graphic organizer
Inherited genes are the
basis of an organism’s
traits.
Lesson 1: Mendel and His Peas
*Mendel performed cross-pollination experiments to
track which traits were produced by specific
parental crosses.
*Mendel found that two factors—one from a sperm
cell and one from an egg cell—control each trait.
*Dominant traits block the expression of recessive
traits. Recessive traits are expressed only when two
recessive factors are present.
Review
What is the name for different
forms of a gene?
A.
B.
C.
D.
alleles
phenotypes
genotypes
chromosomes
*Lesson 2
Review
What is the genotype when two
alleles of a gene are the same?
A.
B.
C.
D.
heterozygous
dominant
homozygous
recessive
*Lesson 2
Review
What occurs when both alleles
can be observed in a phenotype?
A.
B.
C.
D.
incomplete dominance
homozygous
polygenic
codominance
*Lesson 2
Review
According to Mendel, how many
factors controlled each trait?
A.
B.
C.
D.
1
2
3
4
Review
Which of the following describes
alleles that control a trait?
A.
B.
C.
D.
phenotype
codominance
genotype
polygenic inheritance
Understanding Inheritance
*Phenotype describes how a
trait appears.
*Genotype describes alleles
that control a trait.
*Punnett squares and
pedigrees are tools to model
patterns of inheritance.
*Many patterns of inheritance,
such as codominance and
polygenic inheritance, are
more complex than Mendel
described.
Review
If parents have the genotypes
RR and Rr, what percentage of
offspring will have a Rr genotype?
A.
B.
C.
D.
25%
50%
75%
100%
Review
In fruit flies, the allele for red eyes (R)
is dominant over the allele for white
eyes (r). If parents have the genotypes
Rr and Rr, what percentage of
offspring will have red eyes?
A. 25 percent
C.
75 percent
B. 50 percent
D.
100 percent
Review
Heredity is associated with which
of the following?
A.
B.
C.
D.
chromosomes
genes
genotype
all of the above
Review
Which occurs when multiple
genes determine the phenotype
of a trait?
A.
B.
C.
D.
polygenic inheritance
mutation
environmental influence
codominance