Download Section 11.3 - Trimble County Schools

Biology
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11–3 Exploring Mendelian
Genetics
11-3 Exploring Mendelian Genetics
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11–3 Exploring Mendelian Genetics
Independent Assortment
Independent Assortment
To determine if the segregation of one
pair of alleles affects the segregation of
another pair of alleles, Mendel
performed a two-factor cross –
dihybrid cross (1)
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11–3 Exploring Mendelian Genetics
Independent Assortment
The alleles for seed shape
segregated independently of
those for seed color. This
principle is known as
independent assortment (2)
Genes that segregate
independently do not influence
each other's inheritance.
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11–3 Exploring Mendelian Genetics
Independent Assortment
The principle of independent assortment
states that genes for different traits can
segregate independently during the
formation of gametes.
Independent assortment helps account for
the many genetic variations observed in
plants, animals, and other organisms.
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11–3 Exploring Mendelian Genetics
A Summary of Mendel's
Principles
A Summary of Mendel's Principles
•
Genes are passed from parents to their
offspring.
•
If two or more forms (alleles) of the gene for a
single trait exist, some forms of the gene may
be dominant and others may be recessive.
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11–3 Exploring Mendelian Genetics
A Summary of Mendel's
Principles
•
In most sexually reproducing organisms, each
adult has two copies of each gene. These genes
are segregated from each other when gametes
are formed.
•
The alleles for different genes usually segregate
independently of one another.
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Some alleles are neither
dominant nor recessive,
and many traits are
controlled by multiple
alleles or multiple genes.
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Incomplete Dominance
When one allele is not completely
dominant over another it is called
incomplete dominance (1)
In incomplete dominance, the
heterozygous phenotype is between
the two homozygous phenotypes.
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
RR
A cross between
red (RR) and
white (WW) four
o’clock plants
produces pinkcolored flowers
(RW).
WW
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Codominance
In codominance (4)both alleles contribute to the
phenotype.
In certain varieties of chicken, the allele for black
feathers is codominant with the allele for white
feathers.
Heterozygous chickens are speckled with both
black and white feathers. The black and white
colors do not blend to form a new color, but appear
separately.
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Multiple Alleles
Genes that are controlled by more than two alleles
are said to have multiple alleles (5)
An individual can’t have more than two alleles.
However, more than two possible alleles can exist
in a population.
A rabbit's coat color is determined by a single gene
that has at least four different alleles.
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Different combinations of alleles result in the colors
shown here.
KEY
C=
full color; dominant
to all other alleles
cch = chinchilla; partial
defect in pigmentation;
dominant to
ch and c alleles
ch = Himalayan; color in
certain parts of the
body; dominant to
c allele
chhc
ch,cCc
h
ch
AIbino:
Chinchilla:
Himalayan:
cc CC,
cc
c,hCc
, or
cch
c,hhor
cch
c
Full color:
, or
Cc
c = albino; no color;
recessive to all other
alleles
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Polygenic Traits
Traits controlled by two or more genes
are said to be polygenic traits (6)
Skin color in humans is a polygenic trait
controlled by more than four different
genes.
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11–3 Exploring Mendelian Genetics
Applying Mendel's
Principles
Applying Mendel's Principles
Thomas Hunt Morgan used fruit flies to advance
the study of genetics.
Morgan and others tested Mendel’s principles and
learned that they applied to other organisms as
well as plants.
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END OF SECTION