Transcript Genetics - TeacherWeb

Chapter 9
Fundamentals
Of
Genetics
Revised by: R. LeBlanc
Biology
1/’12
Section 1 Mendel’s Legacy
Chapter 9 Objectives
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Describe how Mendel was able to control how his pea
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Describe the steps in Mendel’s experiments on true-
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Distinguish between dominant and recessive traits.
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State two laws of heredity that were developed from
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Describe how Mendel’s results can be explained by
plants were pollinated.
breeding garden peas.
Mendel’s work.
scientific knowledge of genes and chromosomes.
Section 1
Mendel's Legacy
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What is genetics?
The field of biology devoted to
understanding how characteristics
are transmitted from parents to
offspring
Section 1
Introduction to Mendel's Legacy
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How does this alligator differ
from other alligators?
(Notes: This is NOT an albino
and NOT a different species,
but it just has different traits
(genetic condition) which are
rare.)
White and brown are
contrasting traits of skin
color.
What are other
characteristics that are
examples of contrasting
traits?
Did you write down: color,
height, texture, etc
Note: Skin color and eye color are
genetically controlled characteristics of
alligators. Skin traits: white & brown;
eye color traits: blue & brown
Section 1
Mendel's Legacy
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List 5 characteristics that are passed on in
families:
Did you list: eye color, hair color, etc ??
Name one characteristic that may also be
inherited but that is also influenced by
behavior or environment:
Muscle size, body weight, having a
suntan, height.
Mendel’s
Experiment
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Observe the pea
plants in the
given image.
List the
noticeable
characteristics of
the pea plants:
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See the next slide
Mendel’s 7 Characteristics:
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Seed shape
Seed color
Flower color
Flower
position
Pod color
Pod shape
Plant height
Mendel's Legacy
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“Father of Genetics” – 1800’s
Carried out the first experiments on heredity using pea plants.
Carefully controlled his experiments, studying only one trait at a
time and analyzed data mathematically.
Was the first to succeed in predicting how traits are transferred
from generation to generation.
Heredity-Passing on of characteristics from parent to offspring.
Genetics- Branch of biology that studies inherited traits.
Plant reproductive terms
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GAMETES - Male or Female
sex cell. In plants, pollen
(male) and ovule (female).
FERTILIZATION- Fusion of
the male and female
gametes within the flower.
POLLINATION - Transfer of
pollen from the anther to
the pistil, usually by wind,
water, or insects.
CROSS-POLLINATION Transfer of pollen from one
flower (tall) to another
flower (short)
Plant Reproductive Organs
Mendel’s Experiment
Mendel’s Experiments

Mendel bred plants for several
generations that were true-breeding
for specific traits and called these the P
generation.
Offspring of the P generation were
called the F1 generation.
 Offspring of the F1 generation were
called the F2 generation.

Three Steps of Mendel’s
Experiments
Mendel’s Results and Conclusions
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Recessive and Dominant Traits
– Mendel concluded that inherited
characteristics are controlled by
factors that occur in pairs.
– In his experiments on pea plants, one
factor in a pair masked the other. The
trait that masked the other was called
the dominant trait. The trait that was
masked was called the recessive trait.
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Conclusions
Mendel’s Results and Conclusions
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The Law of Segregation
– The law of segregation states that a pair of
factors is segregated, or separated, during the
formation of gametes.
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The Law of Independent Assortment
– The law of independent assortment states that
factors for individual characteristics are
distributed to gametes independent of one
another.
– The law of independent assortment is observed
only for genes that are located on separate
chromosomes or are far apart on the same
chromosome.
Support for Mendel’s Conclusions
We now know that the factors that
Mendel studied are alleles, or
alternative forms of a gene.
 One allele for each trait is passed from
each parent to the offspring.
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Chapter 9
Section 2 Genetic Crosses
Objectives
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Differentiate between the genotype and the phenotype of an
organism.
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Explain how probability is used to predict the results of genetic
crosses.
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Use a Punnett square to predict the results of monohybrid and
dihybrid genetic crosses.
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Explain how a testcross is used to show the genotype of an
individual whose phenotype expresses the dominant trait.
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Differentiate a monohybrid cross from a dihybrid cross.
Chapter 9
Section 2 Genetic Crosses
Calculating Probability
Chapter 9
Section 2 Genetic Crosses
Punnett Square Method for Solving
Genetics Problems
A Cross Between One Pair of Contrasting Traits
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Punnett Square - Prediction of offspring (F1) using genotypes
from parents (P)
Using the letters T= tall and t= short show a cross between a
homozygous dominant and homozygous recessive plant.
Example #1:
The letters T and t
represent alleles
(characteristics of
various traits)
T
T
t
Tt
Tt
t
Tt
Tt
Monohybrid Cross
•Genotype Ratio: This ratio list the number of off-spring with the 3
possible allele combinations:
Homozygous Dominate : Heterozygous : Homozygous Recessive
(PURE DOMINANT : MiXeD DoMiNaNt : pure recessive)
•Phenotype Ratio: This ratio list the number of off-spring with
physical trait characteristics:
Example: # of Tall : # of short
•What would be the Genotype and Phenotype ratios for Example #1?
Genotype Ratio 0 : 4 : 0 (Pure tall / mixed tall / short)
Phenotype Ratio 4 : 0 (Tall / short)
Ex. 2 - Monohybrid Cross
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Show a cross between two heterozygous tall
plants. Complete the Punnett square below
and give the phenotypic and genotypic ratios
for the possible offspring!
T
Phenotype ratio
3:1 (Tall to short)
Genotype ratio
1:2:1
(Homozygous Dominant to
Heterozygous to
Homozygous recessive)
t
T
TT
Tt
t
Tt
tt
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses
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A testcross, in which an individual
of unknown genotype is crossed
with a homozygous recessive
individual, can be used to
determine the genotype of an
individual whose phenotype
expresses the dominant trait.
Section 2 Genetic Crosses
Chapter 9
Testcross
Law of Independent Assortment
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Traits are inherited independently of each other.
To determine which trait a parent will contribute
during fertilization, the F.O.I.L Method is used.
First
Outside
Inside
Last
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Dihybrid cross - Cross between two pairs of contrasting
traits. Ex. Cross a pea plant with heterozygous round
and heterozygous yellow pea plant with a pea plant
that has the same genotype. (Round is dominant over
wrinkled; and Yellow is dominant over green)
First, identify the correct genotype for each parent.
(RrYy x RrYy).
Next, identify all the possible types of gametes each
parent can produce. (use the F.O.I.L. Method)
 RY
Ry rY
ry (see blackboard)
Using a punnett square show the possible offspring that
may be produced from these parents.
Dihybrid Example #1
Each parent produces
4 possible gametes
RY,rY,Ry,ry
RY
rY
Ry
ry
RY
RRYY RrYY RRYy RrYy
rY
RrYY
Ry
RRYy RrYy
RRyy
Rryy
ry
RrYy
rrYy
Rryy
rryy
rrYY RrYy
rrYy
Phenotypic Ratio = 9:3:3:1 (Round and Yellow, Round and Green,
Wrinkled and yellow, Wrinkled and Green)
Dihybrid Example #2
What are the genotype and
phenotype ratios in the offspring
resulting from a cross between two
pea plants; a heterozygous Green,
constricted plant with a yellow ,
heterozygous Smooth plant.
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Note: G = green g = yellow and
N = Smooth n = constricted
Dihybrid Example #2
•Step 1 (Parents
Genotype?)
•Ggnn
x
ggNn
Gn
Gn
gn
gn
•Step 2 (F.O.I.L for each
parents gametes)
gN
GgNn
GgNn
ggNn
ggNn
•Gn Gn gn gn
gn
Ggnn
Ggnn
ggnn
ggnn
•Step 3 (Fill in the Punnett gN
Squares)
gn
•Step 4 (Calculate
Phenotype Ratio (what are
the physical traits)
GgNn
GgNn
ggNn
ggNn
Ggnn
Ggnn
ggnn
ggnn
•gN gn gN gn
Chapter 9
Standardized Test Prep
Multiple Choice
1. What is a procedure in which an individual of
unknown genotype is crossed with a
homozygous recessive individual to determine
the genotype of the unknown individual
called?
A. a monohybrid cross
B. a dihybrid cross
C. a hybrid cross
D. a testcross
Chapter 9
Standardized Test Prep
Multiple Choice, continued
1. What is a procedure in which an individual of
unknown genotype is crossed with a
homozygous recessive individual to determine
the genotype of the unknown individual
called?
A. a monohybrid cross
B. a dihybrid cross
C. a hybrid cross
D. a testcross
Chapter 9
Standardized Test Prep
Multiple Choice, continued
2. In a monohybrid cross of two
heterozygous parents (Pp), what would
the expected genotypes of the offspring
be?
F. 1 PP : 2 Pp : 1 pp
G. 1 pp : 3 PP
H. 3 Pp : 1 pp
J. all Pp
Chapter 9
Standardized Test Prep
Multiple Choice, continued
2. In a monohybrid cross of two
heterozygous parents (Pp), what would
the expected genotypes of the offspring
be?
F. 1 PP : 2 Pp : 1 pp
G. 1 pp : 3 PP
H. 3 Pp : 1 pp
J. all Pp
Chapter 9
Standardized Test Prep
Multiple Choice, continued
3. Which of the following is an example of
a genotype of a heterozygous
individual?
A. p
B. YY
C. Zz
D. rr
Chapter 9
Standardized Test Prep
Multiple Choice, continued
3. Which of the following is an example of
a genotype of a heterozygous
individual?
A. p
B. YY
C. Zz
D. rr