Download Chapter 5 Genetics: The Science of Heredity

Chapter 5 Genetics: The Science of Heredity
Section 1:
Mendel’s Work
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What were the results of Mendel’s
experiments, or crosses?
What controls the inheritance of traits in
organisms?
Chapter 5 Genetics: The Science of Heredity
What is Genetics?
Genetics: the study of heredity
Heredity: the passing of physical characteristics from parents
to offspring
Chapter 5 Genetics: The Science of Heredity
The Father of Genetics
The field of Genetics was
founded by Gregor Mendel, an
Augustinian priest.
Between 1856 and 1863, Mendel
cultivated and tested almost
30,000 pea plants.
The importance of Mendel's work
was not discovered until almost
30 years after Mendel died.
Chapter 5 Genetics: The Science of Heredity
Crossing Pea Plants
Gregor Mendel crossed pea plants that had different traits.
The illustrations show how he did this.
Chapter 5 Genetics: The Science of Heredity
Mendel’s Experiments
In all of Mendel’s crosses, only one form of the trait appeared
in the F1 generation. However, in the F2 generation, the “lost”
form of the trait always reappeared in about one fourth of the
plants.
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
Mendel studied several traits in pea plants.
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
Today, scientists
use the word
“gene” to describe
a piece of DNA
that controls a
trait.
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
The traits that Mendel studied in his pea plant experiments are
controlled by different genes:
GENE
Seed Shape
Seed color
Seed coat color
Pod shape
Pod color
Flower position
Stem height
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
These genes usually have 2 or more alleles, or different forms of
the gene:
GENE
Seed Shape
Seed color
Seed coat color
Pod shape
Pod color
Flower position
Stem height
ALLELE
round
yellow
gray
smooth
green
side
tall
ALLELE
wrinkled
green
white
pinched
yellow
end
short
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
Some of these alleles are known as dominant. Others are known
as recessive:
DOMINANT
RECESSIVE
GENE
ALLELE
ALLELE
Seed Shape
round
wrinkled
Seed color
yellow
green
Seed coat color
gray
white
Pod shape
smooth
pinched
Pod color
green
yellow
Flower position
side
end
Stem height
tall
short
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
In a dominant allele, the trait always shows up as long as there
is at least one dominant allele.
Key
T = tall
t = short
TT
“pure tall”
Tt
“hybrid tall”
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
In a recessive allele, the trait only shows up if both alleles are
recessive.
Key
T = tall
t = short
tt
“pure short”
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
Dominant alleles are always symbolized with capital letters.
Recessive alleles are always symbolized with lower-case letters.
Key for Height
Key for Seed Color
T = tall
t = short
Y = yellow seed color
y = green seed color
Key for Pod Color
Key for Coat Color
G = green pod color
g = yellow pod color
A = gray coat color
a = white coat color
Chapter 5 Genetics: The Science of Heredity
End of Section:
Mendel’s Work
Chapter 5 Genetics: The Science of Heredity
Section 2: Probability
and Heredity
What is probability and how does it help
explain the results of genetic crosses?
What is meant by genotype and phenotype?
What is codominance?
Chapter 5 Genetics: The Science of Heredity
A Punnett Square
The diagrams show how to make a Punnett square. In this
cross, both parents are heterozygous for the trait of seed
shape. R represents the dominant round allele, and r
represents the recessive wrinkled allele.
Chapter 5 Genetics: The Science of Heredity
Probability and Genetics
In a genetic cross, the allele that each parent will pass on to
its offspring is based on probability.
Chapter 5 Genetics: The Science of Heredity
Phenotypes and Genotypes
An organism’s phenotype is its physical appearance, or
visible traits. An organism’s genotype is its genetic makeup,
or allele combinations.
Chapter 5 Genetics: The Science of Heredity
Practicing Punnett Squares
Key for Height
T = tall
t = short
Key for Seed Color
Y = yellow seed color
y = green seed color
Key for Pod Color
G = green pod color
g = yellow pod color
1) T T x T T
2) t t x t t
3) T t x T t
Chapter 5 Genetics: The Science of Heredity
Practicing Punnett Squares
Key for Height
T = tall
t = short
Key for Seed Color
Y = yellow seed color
y = green seed color
Key for Pod Color
G = green pod color
g = yellow pod color
1)
2)
3)
4)
Y
Y
g
G
y
Y
g
g
x
x
x
x
y y
y y
G g
G g
Chapter 5 Genetics: The Science of Heredity
Homozygous vs. Heterozygous
Homozygous = 2 identical alleles
also called “pure” or “purebred”
Examples: T T
tt
Heterozygous = 2 different alleles
also called “hybrid”
Examples: T t
Chapter 5 Genetics: The Science of Heredity
Codominance
In codominance, the alleles are neither dominant nor
recessive. As a result, both phenotypes are expressed in the
offspring.
Chapter 5 Genetics: The Science of Heredity
Incomplete Dominance
In incomplete
dominance, the
contributions of both
alleles are visible and
do not overpower each
other in the phenotype.
As a result, both
phenotypes look
“mixed”.
Chapter 5 Genetics: The Science of Heredity
Dihybrid Cross
Chapter 5 Genetics: The Science of Heredity
Dihybrid Cross
Key for Height
T = tall
t = short
Key for Seed Color
Y = yellow seed color
y = green seed color
Key for Pod Color
G = green pod color
g = yellow pod color
Chapter 5 Genetics: The Science of Heredity
Dihybrid Cross
Chapter 5 Genetics: The Science of Heredity
End of Section:
Probability and Heredity
Chapter 5 Genetics: The Science of Heredity
Section 3: The Cell
and Inheritance
What role do chromosomes play in inheritance?
What events occur during meiosis?
What is the relationship between chromosomes and
genes?
Chapter 5 Genetics: The Science of Heredity
Meiosis
During meiosis, the chromosome pairs separate and are
distributed to two different cells. The resulting sex cells have
only half as many chromosomes as the other cells in the
organism.
Chapter 5 Genetics: The Science of Heredity
Punnett Square
A Punnett square is actually a way to show the events that
occur at meiosis.
Chapter 5 Genetics: The Science of Heredity
A Lineup of Genes
Chromosomes are made up of many
genes joined together like beads on a
string. The chromosomes in a pair may
have different alleles for some genes
and the same allele for others.
Chapter 5 Genetics: The Science of Heredity
Human Chromosomes
Humans have 23 pairs
of chromosomes:
23 from their mother,
and 23 from their father.
Chapter 5 Genetics: The Science of Heredity
Human Chromosomes
The first 22 pairs are
organized and named
according to their size:
Chromosomes #1 are
the largest, #2 are the
second largest, etc.
Chapter 5 Genetics: The Science of Heredity
Human Chromosomes
The final pair of
chromosomes (“X”
and “Y”) are the sex
chromosomes
because they
determine the gender
of the person:
XX = girl
XY = boy
Chapter 5 Genetics: The Science of Heredity
Sex Chromosomes
The father is who determines
the gender of the child since
males need a “Y” chromosome,
and only males have “Y”
chromosomes.
Mother
The mother can only give out an
“X”, and both boys and girls have
at least 1 “X” chromosome.
Father
Chapter 5 Genetics: The Science of Heredity
End of Section: The
Cell and Inheritance
Chapter 5 Genetics: The Science of Heredity
Section 4: Genes, DNA,
and Proteins
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What forms the genetic code?
How does a cell produce proteins?
How can mutations affect an organism?
Chapter 5 Genetics: The Science of Heredity
The DNA Code
Chromosomes are made of DNA. Each chromosome
contains thousands of genes. The sequence of bases in a
gene forms a code that tells the cell what protein to produce.
Chapter 5 Genetics: The Science of Heredity
How Cells Make Proteins
During protein synthesis, the cell uses information from a
gene on a chromosome to produce a specific protein.
Chapter 5 Genetics: The Science of Heredity
Mutations
Mutations can cause a cell to produce an incorrect protein
during protein synthesis. As a result, the organism’s trait, or
phenotype, may be different from what it normally would
have been.
Chapter 5 Genetics: The Science of Heredity
Damages Made by Mutation
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Chapter 5 Genetics: The Science of Heredity
End of Section: Genes,
DNA, and Proteins