11-1
Gregor Mendel
11-2
Punnett Squares
S
Bell Work
S What are dominant and recessive alleles?
Alleles are forms of a gene.
The dominant form of an allele is the form
whose trait shows up if it is present. The recessive
allele is the form whose trait only shows up when
the dominant allele is not present.
Bell Work
Why do children resemble their parents?
They inherit their parents characteristics
through alleles- forms of genes.
11-1
Inheritance
Every living thing has a set of characteristics
inherited from its parent or parents.
Heredity holds the key to understanding what
makes each species unique.
11-1
1. The scientific study of heredity is called _____.
Genetics
11-1 Gregor Mendel
Who was Gregor Mendel?
An Austrian monk, born in 1822.
His experiments with
pea plants laid the
foundations of the science
of genetics.
11-1 Gregor Mendel’s Peas
2. What do we know as true about Gregor Mendel’s
garden peas?
S The male portion of the plant produces sperm (in
pollen). The female portion of the plant produces
egg cells.
S Fertilization produces a new cell, which develops
into a tiny embryo encased within a seed.
S Pea Plants are normally self-pollinating.
11-1
3. What does it mean when pea
plants are described as being true
breeding?
It means that if they are
allowed to self-pollinate,
they would produce identical
offspring.
11-1
4. To perform his experiments, how did Mendel prevent
pea flowers from self-pollinating and control their crosspollination?
To prevent self-pollination, Mendel cut the pollen
bearing male part and dusted this pollen onto another
flower. This process is known as cross-pollination.
11-1
5. Genes –
C chemical factors that determine traits
6. Hybrids
B the offspring of crosses between parents
with different traits
11-1
7. Traits
one
A specific characteristics that vary from
individual to another
8. Alleles
D
different forms of a gene
11-1
9. The principle of dominance states…
that some alleles are dominant and some alleles
are recessive.
10. True or False: An organism with a recessive allele for
a particular form of a trait will always exhibit that form.
False- The organism with a recessive allele will
only exhibit that form when the dominant allele
for the trait is not present.
11-1
11.Which traits were controlled
by dominant alleles in Mendel’s
pea plants?
Tall & Yellow
Which traits were controlled
by recessive alleles?
Short & Green
11-1
Mendel called each original pair of plants the
P Generation (parental) and the offspring of these
the F1 generation (first filial)
Mendel produced hybrids when he crossed
parents with different traits; and to his surprise
the offspring only resembled one of the parents.
11-1 Segregation
Mendel wanted to know the answer to another
question: Had the recessive alleles disappeared,
or were they still present in the F1 plants?
P generation
F1 Generation
F2 Generation
11-1
12. How did Mendel find out whether the recessive alleles
were still present in the F1 plants?
He allowed all seven kinds of F1 hybrid plants to
produce an F2 generation.
11-1
13. About one fourth of the F2 plants from Mendel’s F1
crosses showed the trait controlled by the ______ allele.
Recessive
11-1 Results of the F1 Cross
14. A** Mendel assumed that a dominant allele had masked
the corresponding recessive allele in the F1 generation.
•
However, the trait controlled by the recessive allele showed
up in some of the F2 plants.
•
D ** This reappearance indicated that at some point, the
allele for shortness was segregated, or separated, from the
allele for tallness.
•
Mendel suggested that the alleles for tallness and shortness
in the F1 plants segregated from one another during the
formation of the gametes. 15. What are gametes?
• Gametes are the Sex Cells
F1
Generation
T
17.
t
T
t
Gametes
F2
Generation
T
t
T
t
T T
T t
T t
t t
11-3
17. In the diagram, the dominant allele is
represented by ___ and the recessive allele
is represented by ___.
T dominant
t recessive
11-2
Probability and Punnett Squares
1. The likelihood that a particular event will occur is
called ___________.
Probability
2. What is the probability that a single coin flip will
come up heads?
50%
11-2
3. True or False: The past outcomes of coin flips
greatly affect the outcomes of future coin flips.
False: past outcomes do not affect future ones
4. Why can the principles of probability be used
to predict the outcomes of genetic crosses?
The way in which alleles segregate is
completely random, like a coin flip.
11-2
5. How do geneticists use Punnett Squares?
The gene combinations that might result from
a genetic cross can be determined by drawing a
diagram known as a Punnett Square.
6. How do we complete the Punnett Square for Tt x Tt
T
T
t
t
Tt x Tt Punnett Square
Monohybrid Cross
Complete the Punnett Square:
Punnett Square Solution
11-2 Matching
7. GenotypeD. Genetic makeup of an organism (Tt)
8. Homozygous –
A Organisms that have two identical
alleles for a particular trait (TT or tt)
11-2 Matching
9. PhenotypeC Physical characteristic of an organism
10. HeterozygousB Organisms that have two different
alleles for the same trait (Tt)
11-2
11. True or False: Homozygous organisms are
true-breeding for a particular trait.
True:
TT true-breeding Tt hybrid
12. True or False: Plants with the same
phenotype always have the same genotype.
False
Yellow vs Green Plants
If Y is Dominant Yellow and y is recessive green
Which of the following plants would be yellow?
a. YY
b. Yy
c.
yy
11-2
13. Which are true about probability and
segregation?
B, C, and D
A. Is True If :
In an F1 cross between two hybrid tall pea plants
(Tt), ¼ of the F2 plants will have two alleles for
tallness (TT)
11-2
14. In Mendel’s model of segregation, what was
the ratio of tall plants to short plants in the F2
generation?
3:1
3 Tall plants for every 1 short plant
11-2
15. True or False: Probabilities predict the precise
outcome of an individual event.
False: probabilities predict the average
outcome
16. How can you be sure of getting the expected
50:50 ratio of flipping a coin?
Flip the coin many times
11-2
17. The __________ the number of offspring from a
genetic cross, the closer the resulting numbers will get
to expected values.
larger
18. True or False: The ratios of an F2 generation are
more likely to match Mendelian predicted ratios if
the F1 generation contains hundreds or thousands of
individuals.
True
Check for Understanding
What is the difference between genotype and
phenotype?
Genotype: the set of genes in our DNA
which is responsible for a particular trait.
Phenotype: the physical expression, or
characteristics, of that trait.
11-3
1. In a two-factor cross, Mendel followed _____
different genes as they passed from one
generation to the next.
Two
11-3
2. Phenotype
Genotype
round yellow peas
RRYY
wrinkled green peas
rryy
11-3
3. The F1 offspring of Mendel’s two factor
cross was
c. heterozygous dominant with round
yellow peas RrYy
11-3
4. T/ F The genotypes of the F1 offspring
indicated to Mendel that genes assort
independently.
False
11-3
5. How did Mendel produce the F2
offspring?
self-pollination in F1
11-3
6. Which phenotypes would Mendel expect
to see if genes segregated independently?
c. round and green
d. wrinkled and yellow
11-3
7. What did Mendel observe in the F2
offspring that showed him that the alleles
for seed shape segregate independenlty of
those for seed color?
F2 had combination of phenotypes
not present in the P generation
round green & wrinkled yellow
11-3
8. What were the phenotypes of the F2
generation that Mendel observed?
round green
RRyy
round yellow
RRYY
wrinkled green
rryy
wrinkled yellow
rrYY
11-3
9. What was the ratio of Mendel’s F2
generation for the two-factor cross?
9:3:3:1
10. Complete the Punnett Square to show the
predicted results of Mendel’s two-factor cross
F2 Generation
11-3
11. State Mendel’s principle of
independent assortment:
R genes & Y genes separate
independently during meiosis/
gamete formation.
11-3
12. The following is true about Mendel’s principles:
a. The inheritance of biological
characteristics is determined by genes that are
passed from parents to their offspring.
c. The copies of genes are segregated from
each other when gametes are formed
d. The alleles for different genes usually
segregate independently of one another.
11-3
13. When two or more forms of the gene
for a single trait exist, some forms of the
gene may be ____ and others may be ____
dominant
recessive
11-3
14. T/ F All genes show simple patterns of
dominant and recessive alleles.
False
11-3 Patterns of Inheritance
Incomplete Dominance- One allele is not
completely dominant over another. The
heterozygous phenotype is somewhere in
between the two homozygous phenotypes.
Example: four o’clock flowers
** blended traits
Incomplete Dominance
11-3 Patterns of Inheritance
CoDominance- Both alleles contribute to the
phenotype of the organism.
Example: black, white, and speckled chicken
** both traits shown
CoDominance
11-3 Patterns of Inheritance
Multiple Alleles- Genes have more than
two alleles.
Example: blood type
11-3 Patterns of Inheritance
Polygenic Traits- Two or more genes
control a trait.
Example: skin color
11-3
16. List three criteria Thomas Hunt
Morgan was looking for in a model
organism for genetic studies
small
easy
many offspring in a short time
11-3
17. T/ F Mendel’s principles apply not just
to pea plants but to other organisms as
well.
TRUE
18. Characteristics are determined by
interactions between genes and the _____
Environment
Next…
Quiz over this material (sections 1,2,3)
WEDNESDAY 2-3-16
Punnett Square Practice #1
Due MONDAY 2-1