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A cross between two pea plants with genotypes PpLl and PpLl results in an F1 generation that is 25% PPLL, 50% PpLl, and 25% ppll. Which reason most likely explains why other possible genotypes are not present?- a)The genes underwent independent assortment
- b)The loci of the genes are close together.
- c)The loci of the genes are on different chromosomes.
- d)Crossing over occurred between chromosomes.
Correct answer is option 'B'. Can you explain this answer?
A cross between two pea plants with genotypes PpLl and PpLl results in an F1 generation that is 25% PPLL, 50% PpLl, and 25% ppll. Which reason most likely explains why other possible genotypes are not present?
a)
The genes underwent independent assortment
b)
The loci of the genes are close together.
c)
The loci of the genes are on different chromosomes.
d)
Crossing over occurred between chromosomes.
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Mason Martinez answered |
Understanding the Genetic Cross
In this genetic cross between two pea plants with genotypes PpLl, we observe specific genotypic ratios in the F1 generation. The absence of certain genotypes can be explained by the proximity of the gene loci.
Key Points: Why Other Genotypes Are Absent
- Gene Linkage: The genes P (purple flowers) and L (long pods) are likely located on the same chromosome and are physically close to each other. This proximity leads to a phenomenon known as linkage.
- Independent Assortment: While Mendel's law of independent assortment states that alleles segregate independently, this principle holds true only if the genes are on different chromosomes or far apart on the same chromosome. Because P and L are close together, they are more likely to be inherited as a unit.
- Reduced Recombination: When genes are linked, the chance of recombination (crossing over) occurring between them during meiosis is reduced. As a result, the gametes produced will predominantly carry the parental combinations of alleles (P L and p l).
- Resulting Genotypes: This leads to the observed genotypic ratios: 25% PPLL, 50% PpLl, and 25% ppll, while other combinations such as PpLl and PpLl do not appear due to the lack of recombination between the linked genes.
Conclusion
In summary, the absence of other possible genotypes in this cross is primarily due to the close proximity of the P and L loci on the same chromosome, leading to reduced independent assortment and recombination during gamete formation.
In this genetic cross between two pea plants with genotypes PpLl, we observe specific genotypic ratios in the F1 generation. The absence of certain genotypes can be explained by the proximity of the gene loci.
Key Points: Why Other Genotypes Are Absent
- Gene Linkage: The genes P (purple flowers) and L (long pods) are likely located on the same chromosome and are physically close to each other. This proximity leads to a phenomenon known as linkage.
- Independent Assortment: While Mendel's law of independent assortment states that alleles segregate independently, this principle holds true only if the genes are on different chromosomes or far apart on the same chromosome. Because P and L are close together, they are more likely to be inherited as a unit.
- Reduced Recombination: When genes are linked, the chance of recombination (crossing over) occurring between them during meiosis is reduced. As a result, the gametes produced will predominantly carry the parental combinations of alleles (P L and p l).
- Resulting Genotypes: This leads to the observed genotypic ratios: 25% PPLL, 50% PpLl, and 25% ppll, while other combinations such as PpLl and PpLl do not appear due to the lack of recombination between the linked genes.
Conclusion
In summary, the absence of other possible genotypes in this cross is primarily due to the close proximity of the P and L loci on the same chromosome, leading to reduced independent assortment and recombination during gamete formation.
The X-linked recessive trait of color-blindness is present in 5% of males. If a mother who is a carrier and father who is unaffected plan to have 2 children, what is the probability the children will both be male and color-blind?- a)50%
- b)<1%
- c)25%
- d)6.25%
Correct answer is option 'D'. Can you explain this answer?
The X-linked recessive trait of color-blindness is present in 5% of males. If a mother who is a carrier and father who is unaffected plan to have 2 children, what is the probability the children will both be male and color-blind?
a)
50%
b)
<1%
c)
25%
d)
6.25%
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Orion Classes answered |
Since the mother is a carrier (X-Xc) and the father is unaffected (X-Y), there are four possible combinations of parental gametes: X-X, X-Xc, Y-X, and Y-Xc.
To calculate the probability of having two male children who are both color-blind, we need to consider the probability of each event occurring.
The probability of having a male child is 0.5 (50%). The probability of passing on the color-blindness allele (Xc) from the mother is 0.5 (since she is a carrier).
To calculate the probability of both events occurring, we multiply the individual probabilities:
0.5 x 0.5 = 0.25 or 25%
Therefore, the correct answer is option D, 6.25%.
Suppose the brown allele for eye color (B) is completely dominant over the blue allele for eye color (b). If two brown-eyed parents produce a child that is blue-eyed, what is the probability that at least one out of the next two children they produce will also have blue eyes?- a)2.5%
- b)25%
- c)44%
- d)50%
Correct answer is option 'C'. Can you explain this answer?
Suppose the brown allele for eye color (B) is completely dominant over the blue allele for eye color (b). If two brown-eyed parents produce a child that is blue-eyed, what is the probability that at least one out of the next two children they produce will also have blue eyes?
a)
2.5%
b)
25%
c)
44%
d)
50%
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Orion Classes answered |
If both parents have brown eyes (genotype BB), but they produce a child with blue eyes, it means that both parents must be heterozygous carriers for the blue eye allele (genotype Bb).
There is a 25% chance (1 out of 4) of having a child with the genotype bb, which corresponds to blue eyes.
Now, we need to calculate the probability of having at least one out of the next two children with blue eyes. We can calculate the probability of the complement event (both children having brown eyes) and subtract it from 1 to get the desired probability.
The probability of having both children with brown eyes is (3/4) x (3/4) = 9/16. Therefore, the probability of having at least one child with blue eyes is 1 - (9/16) = 7/16.
Converting 7/16 to a percentage, we get approximately 43.75%, which is closest to option C, 44%.
Suppose that in barley plants, the allele for tall stalks is dominant over short stalks and the allele for wide leaves is dominant over thin leaves. What would be the best way to determine the genotype of a barley plant with a tall stalk and wide leaves?- a)Perform a testcross with a barley plant that has a tall stalk and thin leaves
- b)Perform a testcross with a known heterozygous barley plant
- c)Perform a testcross with a barley plant that has a short stalk and thin leaves
- d)Perform a testcross with a barley plant that has a tall stalk and wide leaves
Correct answer is option 'C'. Can you explain this answer?
Suppose that in barley plants, the allele for tall stalks is dominant over short stalks and the allele for wide leaves is dominant over thin leaves. What would be the best way to determine the genotype of a barley plant with a tall stalk and wide leaves?
a)
Perform a testcross with a barley plant that has a tall stalk and thin leaves
b)
Perform a testcross with a known heterozygous barley plant
c)
Perform a testcross with a barley plant that has a short stalk and thin leaves
d)
Perform a testcross with a barley plant that has a tall stalk and wide leaves
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Orion Classes answered |
he best way to determine the genotype of a barley plant with a tall stalk and wide leaves would be to perform a testcross with a barley plant that has a short stalk and thin leaves.
A testcross involves crossing the individual of unknown genotype with an individual that is homozygous recessive for both traits. In this case, the individual with a short stalk and thin leaves would be homozygous recessive for both the tall stalk and wide leaves alleles.
By performing a testcross with a barley plant that has a short stalk and thin leaves, any offspring that exhibit the recessive traits (short stalk and thin leaves) would indicate that the tested plant is heterozygous for both traits. On the other hand, if all the offspring have the dominant traits (tall stalk and wide leaves), it would suggest that the tested plant is homozygous dominant for both traits.
In a cross of AaBb x AaBb, what fraction of the offspring can be expected to express one of the two dominant alleles, but not both?- a)9/16
- b)1/2
- c)3/8
- d)3/16
Correct answer is option 'C'. Can you explain this answer?
In a cross of AaBb x AaBb, what fraction of the offspring can be expected to express one of the two dominant alleles, but not both?
a)
9/16
b)
1/2
c)
3/8
d)
3/16
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Orion Classes answered |
In a cross of AaBb x AaBb, where A and B represent alleles for two different traits, the possible genotypes of the offspring are:
- AA, Aa, aA, aa (for the A trait)
- BB, Bb, bB, bb (for the B trait)
To determine the fraction of offspring that can be expected to express one of the two dominant alleles, but not both, we need to consider the genotypes that fulfill this condition. In this case, it would be the offspring with genotypes AaBb and Aabb (expressing the dominant A allele and the dominant B allele, respectively).
Out of the total of 16 possible combinations (4 possible genotypes for each parent), there are 2 combinations that meet this criterion (AaBb and Aabb). Therefore, the fraction of the offspring that can be expected to express one of the two dominant alleles, but not both, is 2/16, which simplifies to 1/8.
If two genes experience independent assortment, which assumption is most likely true?- a)They are located in close proximity on the same chromosome.
- b)Crossing over between the genes does not occur.
- c)The genes are located on different chromosomes or are far apart on the same chromosome.
- d)The expression of one gene does not affect the expression of the other.
Correct answer is option 'C'. Can you explain this answer?
If two genes experience independent assortment, which assumption is most likely true?
a)
They are located in close proximity on the same chromosome.
b)
Crossing over between the genes does not occur.
c)
The genes are located on different chromosomes or are far apart on the same chromosome.
d)
The expression of one gene does not affect the expression of the other.
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Orion Classes answered |
Independent assortment refers to the random segregation of alleles for different genes during the formation of gametes. This process occurs when genes are located on different chromosomes or are far apart on the same chromosome. In these cases, the genes are more likely to assort independently, meaning their inheritance is not linked or dependent on each other.
In the ABO blood group system in humans, if a person of type-B blood has children with a person of type-AB blood, what blood types could their children have?- a)Type-AB, type-A, and type-B
- b)Type-B and type-AB
- c)Type-AB, type-A, type-B, and type-O
- d)Type-A and type-B
Correct answer is option 'A'. Can you explain this answer?
In the ABO blood group system in humans, if a person of type-B blood has children with a person of type-AB blood, what blood types could their children have?
a)
Type-AB, type-A, and type-B
b)
Type-B and type-AB
c)
Type-AB, type-A, type-B, and type-O
d)
Type-A and type-B
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Orion Classes answered |
When a person with type-B blood (genotype BO) has children with a person with type-AB blood (genotype AB), their children can inherit the following blood types:
- Type-AB: The children can inherit the A and B alleles from the type-AB parent, resulting in type-AB blood.
- Type-A: The children can inherit the A allele from the type-AB parent or the B allele from the type-B parent, resulting in type-A blood.
- Type-B: The children can inherit the B allele from the type-B parent, resulting in type-B blood.
Therefore, the possible blood types for their children are type-AB, type-A, and type-B.
A gene for corn has two alleles, one for yellow kernels and one for white kernels. Cross pollination of yellow corn and white corn results in ears of corn that have an approximately even mix of yellow and white kernels. Which term best describes the relationship between the two alleles?- a)Genetic recombination
- b)Codominance
- c)Incomplete dominance
- d)Chimerism
Correct answer is option 'B'. Can you explain this answer?
A gene for corn has two alleles, one for yellow kernels and one for white kernels. Cross pollination of yellow corn and white corn results in ears of corn that have an approximately even mix of yellow and white kernels. Which term best describes the relationship between the two alleles?
a)
Genetic recombination
b)
Codominance
c)
Incomplete dominance
d)
Chimerism
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Orion Classes answered |
Codominance occurs when both alleles of a gene are expressed equally in the phenotype of a heterozygous individual. In the case of the corn kernels, the yellow allele and the white allele are both expressed in the phenotype, resulting in an approximately even mix of yellow and white kernels in the ears of corn. Neither allele is dominant over the other, and they are both fully expressed.
Therefore, option B, "Codominance," is the correct term to describe the relationship between the yellow and white alleles for corn kernel color.
In labrador retrievers, the allele for black coat color (B) is dominant to the allele for brown coat color (b). However, if a lab has two copies of the recessive allele for a pigment-depositing gene (e), it can only have yellow coat color. In a cross of two doubly heterozygous black labs (BbEe x BbEe), what fraction of the next generation would one expect to be yellow?- a)3/16
- b)1/8
- c)1/16
- d)1/4
Correct answer is option 'D'. Can you explain this answer?
In labrador retrievers, the allele for black coat color (B) is dominant to the allele for brown coat color (b). However, if a lab has two copies of the recessive allele for a pigment-depositing gene (e), it can only have yellow coat color. In a cross of two doubly heterozygous black labs (BbEe x BbEe), what fraction of the next generation would one expect to be yellow?
a)
3/16
b)
1/8
c)
1/16
d)
1/4
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Orion Classes answered |
From the Punnett square, we can see that there are 4 genotypes (BbEe, BBEe, BbEE, bbEe) that correspond to a yellow coat color. Out of the 16 possible offspring, 4 have the genotype for yellow coat color.
Therefore, the fraction of the next generation that would be expected to be yellow is 4/16, which simplifies to 1/4.
Therefore, the correct option is D. 1/4.
Suppose a white-furred rabbit breeds with a black-furred rabbit and all of their offspring have a phenotype of gray fur. What does the gene for fur color in rabbits appear to be an example of?- a)Mosaicism
- b)Codominance
- c)Incomplete dominance
- d)Complete dominance
Correct answer is option 'C'. Can you explain this answer?
Suppose a white-furred rabbit breeds with a black-furred rabbit and all of their offspring have a phenotype of gray fur. What does the gene for fur color in rabbits appear to be an example of?
a)
Mosaicism
b)
Codominance
c)
Incomplete dominance
d)
Complete dominance
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Orion Classes answered |
The observed phenotype of the offspring, which is gray fur resulting from the cross between a white-furred rabbit and a black-furred rabbit, suggests that the gene for fur color exhibits incomplete dominance. In incomplete dominance, neither allele is completely dominant over the other, and the heterozygous phenotype is an intermediate or blended expression of both alleles.
In this case, the white fur allele and the black fur allele are not exhibiting complete dominance, where one allele would completely mask the expression of the other. Instead, they are interacting in a way that produces an intermediate phenotype (gray fur) in the heterozygous offspring.
Mosaicism refers to the presence of cells with different genotypes in an organism, typically arising from somatic mutations during development and leading to phenotypic variation within tissues.
Codominance occurs when both alleles of a gene are expressed simultaneously and visibly in the phenotype, such as the A and B alleles in the ABO blood group system.
Complete dominance occurs when one allele is fully dominant over the other, resulting in the complete expression of the dominant allele's phenotype and the masking of the recessive allele's phenotype.
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