Transcript 11–3 Exploring Mendelian Genetics

11–3 Exploring Mendelian
Genetics
11-3 Exploring Mendelian Genetics
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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.
In incomplete dominance, the heterozygous
phenotype is between the two homozygous
phenotypes. It is a form of intermediate that results
in a third phenotype.
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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, 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
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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.
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
Multiple Alleles
• Blood type is an example of a common multiple
allele trait. There are 3 different alleles for blood
type, (A, B, & O).
• A is dominant to O. Therefore, A is dominant and O
is recessive.
• B is also dominant to O. Therefore, B is dominant
and O is recessive.
• A and B are both codominant.
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11–3 Exploring Mendelian Genetics
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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.
Skin color in humans is a polygenic trait controlled
by more than four different genes.
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11–3 Exploring Mendelian Genetics
AaBbCc
aabbcc
Aabbcc
AaBbCc
AaBbcc AaBbCc AABbCc AABBCc AABBCC
20/64
15/64
Fraction of progeny
LE 14-12
6/64
1/64
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11–3 Exploring Mendelian Genetics
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11–3 Exploring Mendelian Genetics
• An epistatic gene can interfere with other genes.
It can mask the phenotypic effect of another gene.
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11–3 Exploring Mendelian Genetics
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11–3 Exploring Mendelian Genetics
• The environment interacts
with genotype.
• Phenotype is a combination of
genotype and environment.
• The sex of sea turtles depends
on both genes and the
temperature of the nest (cooler
temps produce males, warmer
temps produce females and a
pivotal temp that would produce
equal).
• Height and weight is another
example of a phenotype
affected by the environment
(nutrition and exercise).
• Nature vs nurture
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11–3
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Continue to:
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11–3
In a cross involving two pea plant traits,
observation of a 9 : 3 : 3 : 1 ratio in the F2
generation is evidence for
a. the two traits being inherited together.
b. an outcome that depends on the sex of the
parent plants.
c. the two traits being inherited independently
of each other.
d. multiple genes being responsible for each
trait.
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Traits controlled by two or more genes are
called
a. multiple-allele traits.
b. polygenic traits.
c. codominant traits.
d. hybrid traits.
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11–3
In four o'clock flowers, the alleles for red flowers
and white flowers show incomplete dominance.
Heterozygous four o'clock plants have
a. pink flowers.
b. white flowers.
c. half white flowers and half red flowers.
d. red flowers.
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11–3
A white male horse and a tan female horse
produce an offspring that has large areas of
white coat and large areas of tan coat. This is
an example of
a. incomplete dominance.
b. multiple alleles.
c. codominance.
d. a polygenic trait.
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Mendel's principles apply to
a. pea plants only.
b. fruit flies only.
c. all organisms.
d. only plants and animals.
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