All AP Biology Resources
Example Questions
Example Question #4 : Understand Epistasis
Epistasis controls the color of squash, with the B locus controlling color (yellow is dominant to green), and E locus determining expression of B locus. This is a case of dominant epistasis. Which of the following is true?
bbEe results in yellow squash
bbee results in yellow squash
bbEe results in green squash
Bbee results in yellow squash
Bbee results in yellow squash
Epistasis describes the interaction of genes, where the epistatic locus masks the effects of a gene at another locus. In this example, locus E is epistatic. As this is stated to be dominant epistasis, when the E locus is either Ee or EE this locus will mask the effect of the B locus (color). Thus, any combination of B/b with Ee or EE will result in white squash. When the E locus is homozygous recessive (ee), the effect of the B locus will not be masked. Thus, BbEe will result in yellow squash as ee will not mask the color, and B (yellow) is dominant.
Example Question #1 : Understand Epistasis
Snapdragons’ color is controlled by recessive epistasis, with the B locus controlling color and the A locus determining expression of B locus. B (red) is dominant to b (yellow) Which of the following is false?
bbaa results in yellow snapdragon
bbAA results in yellow snapdragon
bbAa results in yellow snapdragon
BbAA results in red snapdragon
bbaa results in yellow snapdragon
Epistasis describes the interaction of genes, where the epistatic locus masks the effects of a gene at another locus. In this example, locus A is epistatic. As this is stated to be recessive epistasis, when the A locus is aa this locus will mask the effect of the B locus (color). Thus, any combination of B/b with aa will result in white snapdragon. Thus, bbaa will result in white snapdragon, as the epistatic locus will mask the effect of the B locus.
Example Question #81 : Inheritance
A mother with type A blood and a father with type B blood have a child. What blood type is impossible for that child to have?
AB
A
B
All are possible
O
All are possible
The mother's possible genotypes for blood are AO and AA, while the father's are BO and BB; therefore, the child could have any blood type because we could receive an O allele from either parent.
The full possibilities are:
A from mother, O from father - blood type A
A from mother, B from father - blood type AB
O from mother, B from father - blood type B
O from mother, O from father - blood type O
Example Question #82 : Inheritance
In a specific type of flower the genes coding for color display codominance. What would you expect the phenotype to be for a cross between a flower homozygous for white coloration and a flower homozygous for red coloration?
Red
Distinct red and white spots
Pink
White
Distinct red and white spots
Codominance is a phenomenon in which the phenotypes associated with both alleles will be expressed in their entirety. This expression pattern results in mottled expression, creating distinct red and white spots for the flower. This is different than incomplete dominance, in which the two phenotypes appear to blend together.
Example Question #83 : Inheritance
In humans, blood type is determined by three alleles: A, B, and O. Both the A and B alleles are dominant to the O allele. When both A and B are present, however, a combined phenotype of AB results. In AB individuals, both A and B antigens are fully expressed on the cell surface. This is an example of __________.
complete dominance
nondominance
codominance
Mendelian dominance
incomplete dominance
codominance
Since the A and B alleles both seem to exert a form of dominance, this is clearly not our common example of a complete dominance scenario. We can conclude that blood type is determined by either incomplete dominance or codominance.
In incomplete dominance, both alleles exert influence to a lesser degree resulting in a "blended" phenotype. In blood type, both alleles exert their full influence together. Instead of yielding a blended phenotype, this situation results in a phenotype that is functionally equivalent to having both A and B blood types at once. The A and B alleles are codominant.
Example Question #302 : Evolution And Genetics
Scientists are trying to figure out the dominance hierarchy for a newly discovered plant. They have found that when a true-breeding yellow plant is crossed to a true-breeding green plant, the resulting offspring have distinct spots of yellow and green. What is the most likely explanation for this result?
Yellow is the dominant allele
Green is the dominant allele
Codominance
Incomplete dominance
Codominance
In the resulting offspring, both phenotypes are displayed equally. This is a classic example of codominance. If an intermediate phenotype was observed, incomplete dominance would be the correct answer.
In codominance, both alleles are considered dominant. This means that both alleles will be fully expressed in different regions, resulting in spots. In incomplete dominance neither allele is fully dominant, so both can be expressed simultaneously in a given area. The result is a blending of both alleles.
Example Question #1 : Understand Co Dominance
The shorthorn cattle coat color exhibits codominance. If a homozygous red individual and homozygous white individual produce an offspring, what will the resulting coat color be?
White
Pink
Red
Roan
Roan
In cases of codominance, the offspring have both alleles expressed at the same time. Thus, the coat color will be roa, which contains both white and red hair.
Example Question #5 : Understand Co Dominance
Blood type exhibits codominance. and are dominant alleles, and i is recessive. results in blood type , results in blood type , and i results in blood type . If an individual with genotype produces offspring with an individual with blood type what will be the blood type of the resulting offspring?
A
A
AB
O
AB
In cases of codominance, the offspring have both alleles expressed at the same time. As both and are dominant alleles, the resulting offspring will have blood type .
Example Question #84 : Inheritance
Which of the following describes a single genetic locus that controls more than one trait?
Pleiotropic
Epistatic
Polysomatic
Polygenic
Somatic
Pleiotropic
The ability of a gene to affect an organism is multiple ways is called pleiotropy. During post-transcriptional modification, introns are removed from the mRNA sequence and exons are spliced together to create the desired protein product. By splicing the gene in different ways, different proteins can be produced, which will affect different traits.
Consider the sentence: The man ran on the track, but fell.
By splicing different portions of the sentence, it can take on different meanings: The man ran. The man on the track fell. The man fell. The man ran, but fell.
Where pleiotropic genes affect more than one trait, polygenic traits are affected by multiple genes. Epistatic genes are regulated by the activation of other genes.
Example Question #2 : Understand Incomplete Dominance
Scientists are trying to figure out the dominance hierarchy for a newly discovered plant. They have found that when a true-breeding red plant is crossed to a true-breeding blue plant, the resulting offspring are purple. What is the most likely explanation for this result?
Red is the dominant allele
Incomplete dominance
Codominance
Blue is the dominant allele
Incomplete dominance
An intermediate phenotype is observed in the offspring. This is a classic example of incomplete dominance. Neither allele is dominant over the other, allowing both phenotypes to be expressed simultaneously. A plant expressing both blue and red will appear purple.
Codominance refers to a dominance pattern in which both alleles are dominant, and cannot be expressed simultaneously. Certain regions will express one dominant allele, while other regions will express the other allele. The result is a mottled or spotted appearance.
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