Transcript Slide 1

Name a food that does not have DNA.
If you were talking to your friend on a cell
phone how would you describe this person?
If you were talking to your friend on a cell
phone how would you describe this person?
•Widow’s peak
• Red Hair
•Cleft Chin
•Freckles
•Detached earlobes
•Female
•Age (20’s)
How would you describe this person? Write down 10 things.
How would you describe this person? Write down 10 things.
•Male
•Brown Hair
•Blue eyes
•Detached Earlobes
•Cleft Chin
•No Widow’s Peak
•Age (20’s)
Phenotype:
In Heredity, when we are talking about
a measurable and observable
characteristic of an organism, we refer to
it as a Phenotype.
Circle the words on your list that can be
measured or observed. Those are phenotypes.
Examples of characteristics that can not be
measured would include: cute, pretty, handsome,
weird or talented.
Gregor Mendel was curious about
characteristics and wondered if he could
predict what characteristics an offspring
would have by looking at the parents. (See
biography handout to learn more about his
life)
Mendel observed and recorded the
characteristics of pea plants that he grew for a
number of years. He started to see a pattern.
The pea plants that grew tall for many generations, he
called “purebred” tall. The purebred tall pea plant always
had tall offsprings.
T = Tall
T
T
T
TT
TT
T
TT
TT
The short pea plants always had short offsprings.
t
t
t
tt
tt
t
tt
tt
t = short
And when Mendel combined the pure
tall with the short peas, all the
offspring were tall.
T
T
t
Tt
Tt
t
Tt
Tt
Tt = Tall
So Mendel wondered what would happen if these
offspring were combined.
Expecting to find all the offspring to be tall like their
parents, he discovered some of the offspring were short.
In fact, about a forth were short. He created a theory that each
parent passed two factors to each offspring. And that by
“crossing” these factors one could predict the probability of the
offspring having a certain characteristic. The crossing tool used to
calculate the odds of an offspring’s characteristic is called the
Punnett Square.
Mendel called the pea plants that had a tall
factor and a short factor a hybrid. Pea plants
that were “pure” tall or short were called
homozygous.
Tt = Tall
T
t
T
t
(tall)
(tall)
TT
Tt
(tall)
(short)
Tt
tt
Mendel called the characteristic that was hidden,
the “recessive” factor. And the characteristic that
was observed, the “dominant” factor.
What is an offspring called if it has a
dominant and a recessive gene?
VOCABULARY
sexual reproduction
p. 102
gene p. 102
heredity p. 102
allele p. 103
phenotype p. 106
genotype p. 106
dominant p. 107
recessive p. 107
During sexual reproduction a cell
containing genetic information from the
mother and a cell containing genetic
information from the father combine into
a completely new cell, which becomes
the offspring.
A gene is a unit of heredity that occupies a
specific location on a chromosome and codes
for a particular product.
Heredity is the passing of genes from parents
to offspring.
The various forms of the same gene are
called alleles (uh-LEELZ).
An organism's phenotype describes the
actual characteristics that can be
observed.
Genotype is the name for the genes an
organism has.
A dominant allele is one that is expressed
in the phenotype even if only one copy is
present in the genotype—that is, even if
the other allele is an alternative form.
A recessive allele is one that is expressed in
the phenotype only when two copies of it are
present on the homologs.
How would you show the relationship
between a hybrid and its purebred
parents using a Venn diagram?
1. Explain the difference between acquired and inherited
traits.
2. Describe the conclusions that Mendel drew from his
experiments with pea plants.
3. What type of alleles are expressed only if two identical
copies exist on the homologs of the offspring?
4. Compare and Contrast What is the difference between a
genotype and a phenotype?
5. Analyze Explain why a person with an allele for a particular
trait may not have a phenotype that shows the trait.
6. Apply In guinea pigs, the allele for black fur is dominant
over the allele for brown fur. If you had two parent guinea
pigs, each with brown fur, what color fur might the offspring
have, and why?
VOCABULARY
Punnett square p. 110
ratio p. 112
probability p. 112
percentage p. 112
A ratio compares, or shows the relationship
between, two quantities. A ratio is usually
written 4:4 and read as “four to four.” This can
be interpreted as “four out of four.” The
Punnett square shows that four out of four
offspring will express the dominant gene for
regular height.
A Punnett square illustrates how the
parents' alleles might combine in
offspring.
Punnett squares and the ratios they show
express probability. Probability is the
likelihood, or chance, of a specific
outcome in relation to the total number
of possible outcomes. The ratios derived
from a Punnett square tell you the
probability that any one offspring will get
certain genes and express a certain trait.
Another way of expressing probability is
as a percentage. A percentage is a ratio
that compares a number to 100.
Homozygous: Both alleles are dominant
or recessive. This would be a
characteristic of a purebred. An
example would be TT, tt, SS, ss, LL or ll.
Heterozygous: The alleles are different.
This would be a hybrid. An example would
be Tt, Ss or Ll.
1. Explain how Punnett squares predict the outcomes of heredity.
2. How are ratio and percentages related?
3. How can you find a percentage chance from a Punnett square?
4. Predict Mendel studied the colors of seeds in his
experiments with pea plants. Let G stand for green and g
stand for yellow. Green is dominant. Make a Punnett square for
a cross between two Gg plants. Find the percentage chance for
each outcome.
5. Apply In pea plants, the allele for smooth peas is dominant
over the allele for wrinkled peas. Create a Punnett square and
calculate the probability that two smooth-pea plants will have
an offspring with wrinkled peas if each parent has one smooth
and one wrinkled allele.
Identify the following alleles
as Homozygous (HO) or
Heterozygous (HE):
LL, Ss, EE, ee, Ee, Ll, SS, ss
Mendel’s Law of Dominance:
When there is a dominant and
recessive allele, the dominant
one will be expressed and the
recessive one will be hidden.
Example: B is dominant for eye color
brown. b is recessive for eye color
blue. A person with genotype Bb for
eye color will have brown eyes.
Mendel’s Law of Segregation: Allele pairs
separate during gamete formation. One of
those alleles is passed down randomly to the
offspring.
Example: Father has BB genotype for eye
color. Mother has Bb genotype for eye
color. Father will pass down one B, Mother
will pass down either a B or b.
How is it possible for two brown
eyed parents to have 3 blue
eyed offsprings if brown is
dominant over blue for eyes?
ABO blood types are inherited through genes and they do
not change as a result of environmental influences during
life. An individual's ABO type is determined by the
inheritance of 1 of 3 alleles (A, B, or O) from each
parent. The possible outcomes are shown below:
Parent Alleles
A
B
O
A
AA
(A)
AB
(AB)
AO
(A)
B
AB
(AB)
BB
(B)
BO
(B)
O
AO
(A)
BO
(B)
OO
(O)
GENOTYPE
(PHENOTYPE)
GENOTYPE
(PHENOTYPE)
GENOTYPE
(PHENOTYPE)
Parent
Alleles
A
B
O
A
AA
(A)
AB
(AB)
AO
(A)
B
AB
(AB)
BB
(B)
BO
(B)
O
AO
(A)
BO
(B)
OO
(O)
Both A and B alleles are dominant over O. As a result,
individuals who have an AO genotype will have an A
phenotype. People who are type O have OO genotypes. In
other words, they inherited a recessive O allele from both
parents. The A and B alleles are codominant. Therefore, if an
A is inherited from one parent and a B from the other, the
phenotype will be AB. Agglutination tests will show that
these individuals have the characteristics of both type A and
type B blood.
What is codominance?
Sickle Cell
Anemia