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>Incomplete dominance >
>Incomplete dominance is a genetic pattern where the offspring of two
parents with different traits have an intermediate phenotype that is a blend
of both traits, rather than one trait dominating over the other. >
>Explanation >
>Incomplete dominance is a pattern of inheritance in which the heterozygous
genotype results in a phenotype that is intermediate between the two
homozygous phenotypes. This means that neither allele is dominant over the
other, and both contribute to the resulting phenotype. For example, in
snapdragons, a red flowered plant crossed with a white flowered plant
produces offspring with pink flowers, which is an intermediate phenotype
between red and white. Incomplete dominance can be observed in various
traits such as hair texture, skin color, and blood type in humans. >
Example
>Snapdragon flower is a classic example of incomplete dominance. When a
homozygous red flowered snapdragon plant is crossed with a homozygous white
flowered plant, the resulting offspring (F1 generation) have pink flowers.
The pink flower color is an intermediate phenotype that results from
incomplete dominance, where neither the red nor the white allele is fully
dominant over the other. This means that both alleles are expressed, and the
resulting phenotype is a blend of both traits. When two F1 plants are
crossed, the resulting F2 generation can have red, pink, or white flowers in
a 1:2:1 ratio. >
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>Co-dominance >
>Co-dominance is a genetic concept that describes a relationship between two
versions (alleles) of a gene, in which both alleles are expressed equally in
the phenotype of the individual. This means that both traits are visible and
distinct in the organism, rather than being blended or dominated by one
allele over the other. For example, in humans, the ABO blood group system is
an example of co-dominance, where both the A and B alleles are expressed
equally, resulting in individuals with AB blood type expressing both A and B
antigens on their red blood cells. >
Explanation
>Co-dominance is a genetic pattern that occurs when both alleles of a gene
are expressed equally in the phenotype of an organism. This means that
neither allele is dominant over the other, and both alleles are fully
expressed in the phenotype. >
>In other words, if an individual inherits two different alleles for a
gene, both traits will be visibly expressed in the individual. This is in
contrast to dominant-recessive inheritance, where only one allele is
expressed in the phenotype while the other remains hidden. >
Example
>In the case of ABO blood groups, individuals can inherit two different
alleles, A and B. In a person who inherits one A allele and one B allele,
both the A and B antigens will be expressed on their red blood cells,
resulting in the AB blood type. Neither A nor B is dominant over the
other, and both alleles are equally expressed, leading to the co-dominant
expression of both antigens. >
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>Another example of co-dominance can be observed in flower color
inheritance in some plants. For instance, if a red-flowered plant and a
white-flowered plant are crossed, the resulting offspring may display a
phenotype that is intermediate between the two colors. However, in some
cases, the red and white traits may be co-dominant, resulting in a
pink-flowered offspring where both red and white traits are equally
expressed. >
>
>
In incomplete dominance, neither allele is completely dominant over
the other, resulting in a phenotype that is a blend of the two,
whereas in co-dominance, both alleles are expressed equally in the
phenotype.
In incomplete dominance, the heterozygous offspring have an
intermediate phenotype, while in co-dominance, the heterozygous
offspring have a phenotype that expresses both alleles.
In incomplete dominance, the ratio of the genotypes in the offspring
is 1:2:1, while in co-dominance, the ratio of the genotypes in the
offspring is 1:2:1.
In incomplete dominance, the ratio of the phenotypes in the offspring
is 1:2:1, while in co-dominance, the ratio of the phenotypes in the
offspring is 1:2:1.
In incomplete dominance, an example is a cross between a red flower
and a white flower resulting in a pink flower, while in co-dominance,
an example is a cross between a black chicken and a white chicken
resulting in a speckled chicken.
In incomplete dominance, the alleles are not fully expressed, while in
co-dominance, both alleles are fully expressed.
In incomplete dominance, the alleles are not equally dominant, while
in co-dominance, both alleles are equally dominant.
In incomplete dominance, the phenotypic and genotypic ratios are
different, while in co-dominance, the phenotypic and genotypic ratios
are the same.
In incomplete dominance, the blending of alleles occurs, while in
co-dominance, the expression of both alleles occurs.
In incomplete dominance, the heterozygous individual is distinct from
both homozygous parents, while in co-dominance, the heterozygous
individual is a blend of both homozygous parents.
>Understanding the concept of partial dominance >
>
Partial dominance is a type of inheritance pattern in which one allele is
not completely dominant over the other, resulting in a phenotype that is
intermediate between the two homozygous phenotypes. In other words, it is
an example of incomplete dominance where the phenotype of the heterozygote
is somewhere between the phenotype of the homozygous dominant and
homozygous recessive genotypes.
For example, consider a flower species where red flowers (RR) are
completely dominant over white flowers (rr). In partial dominance, when a
heterozygous red (Rr) flower is crossed with another heterozygous red (Rr)
flower, the offspring can have a phenotype that is a shade of pink, which
is intermediate between red and white.
In partial dominance, the ratio of the genotypes in the offspring is still
1:2:1, as in incomplete dominance and co-dominance. However, the ratio of
the phenotypes in the offspring is not the same as the genotypic ratio,
and it depends on the degree of dominance of the alleles.
Partial dominance can also be observed in traits such as skin color and
height in humans, where the phenotype of the heterozygous individual is
intermediate between that of the homozygous dominant and homozygous
recessive individuals.
partial dominance is an important concept in genetics that helps explain
the inheritance of traits where neither allele is completely dominant over
the other, resulting in a phenotype that is a blend of both.
>
>
Incomplete dominance and co-dominance are two common inheritance patterns
that are observed in genetics.
Incomplete dominance occurs when neither of the two alleles in a
heterozygous individual is completely dominant over the other, and the
resulting phenotype is a blend of the two. This means that the
heterozygous offspring will have a phenotype that is intermediate between
the two homozygous phenotypes. For example, in snapdragons, the allele for
red flowers (RR) is incompletely dominant over the allele for white
flowers (rr). So, when a red-flowered plant is crossed with a
white-flowered plant, the offspring have pink flowers, which is a blend of
red and white.
Co-dominance, on the other hand, occurs when both alleles in a
heterozygous individual are expressed equally, and the resulting phenotype
displays traits of both alleles. This means that the heterozygous
offspring will have a phenotype that expresses both alleles equally. For
example, in human blood type inheritance, the A and B alleles are
co-dominant, and individuals with the AB genotype express both A and B
antigens on their red blood cells.
In both incomplete dominance and co-dominance, the ratios of genotypes and
phenotypes in the offspring follow the Mendelian principles of
inheritance, with a 1:2:1 genotype ratio and a 1:2:1 phenotype ratio for
each type of inheritance.
Understanding these inheritance patterns is important in predicting the
traits of offspring from a cross between two parents with different
alleles. By knowing whether the alleles are incompletely dominant or
co-dominant, we can predict the likely phenotypes of the offspring and the
ratios of each genotype and phenotype that will result.
>
>> >Sickle cell anemia is a genetic disorder that results from a co-dominant
inheritance pattern in humans. The disorder is caused by a mutation in the
HBB gene that codes for the beta-globin subunit of hemoglobin, the protein
that carries oxygen in the blood. >
>The HBB gene has two common alleles: the normal allele, denoted as HbA, and
the mutated allele, denoted as HbS. In individuals with sickle cell anemia,
they inherit two copies of the HbS allele, resulting in the production of
abnormal hemoglobin molecules that cause red blood cells to assume a sickle
shape. This sickling of red blood cells can lead to a variety of health
problems, including anemia, organ damage, and pain. >
>However, individuals who inherit one copy of the HbS allele and one copy of
the HbA allele have a condition called sickle cell trait, which is a milder
form of the disorder. In these individuals, the HbS and HbA alleles are
co-dominant, and both types of hemoglobin are produced in equal amounts. As
a result, individuals with sickle cell trait have some abnormal hemoglobin
molecules but enough normal hemoglobin to prevent the sickling of red blood
cells under normal conditions. >
>The co-dominant inheritance of the HbS and HbA alleles means that
individuals with sickle cell trait can pass on either the HbS or HbA allele
to their offspring with equal probability. As a result, the inheritance of
the sickle cell trait follows a simple Mendelian pattern, with a 1:2:1
genotype and phenotype ratio. >
>the co-dominant inheritance pattern of sickle cell anemia in humans
provides an example of how genetic disorders can result from the expression
of both alleles in a heterozygous individual. Understanding the co-dominant
inheritance of this disorder is important for genetic counseling and for
developing treatments and preventive measures. >
>
examples > >
>
Incomplete dominance: Flower color in snapdragons - Students can be shown
pictures of red and white snapdragon flowers, and then a picture of a pink
snapdragon flower. The pink color is the result of incomplete dominance,
where the red and white alleles are not completely dominant over each
other and blend to create a new phenotype.
Incomplete dominance: Feather color in chickens - Students can be shown
pictures of black-feathered chickens and white-feathered chickens, and
then a picture of a gray-feathered chicken. The gray color is the result
of incomplete dominance, where the black and white alleles are not
completely dominant over each other and blend to create a new phenotype.
Co-dominance: Blood type in humans - Students can be shown pictures of
different blood types, such as A, B, AB, and O. They can then learn that
the A and B alleles are co-dominant, and that individuals with the AB
genotype express both A and B antigens on their red blood cells.
Co-dominance: Coat color in cattle - Students can be shown pictures of red
and white cattle, and then a picture of a cattle with patches of both
colors. The patches of both colors are the result of co-dominance, where
the red and white alleles are both expressed in the phenotype.
Incomplete dominance: Skin color in humans - Students can be shown
pictures of individuals with light skin and individuals with dark skin,
and then a picture of an individual with intermediate skin color. The
intermediate skin color is the result of incomplete dominance, where the
alleles for light and dark skin are not completely dominant over each
other and blend to create a new phenotype.
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