AP Biology : Understand epistasis
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Example Questions
Example Question #1 : Understand Epistasis
Epistasis controls the fur color of labradors, with the B locus controlling color (Black is dominant to brown), and E locus determining expression of B locus. This is a case of recessive masking epistasis. Which of the following is true?
BBee results in black fur
bbee results in brown fur
BbEe results in black fur
bbEe results in black fur
BbEe results in black fur
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 recessive masking epistasis, when the E locus is homozygous recessive (ee), this locus will mask the effect of the B locus (color). Thus, any combination of B/b with ee will result in yellow fur. When the E locus is heterozygous (Ee) or homozygous dominant (EE), the effect of the B locus will not be masked. Thus, BbEe will result in black fur (as black B is dominant to brown b), and the E locus does not mask the B locus here, as the E locus is heterozygous in this individual (Ee).
Example Question #1 : Understand Epistasis
When two genes interact, and one gene masks the expression of a second gene, the first gene is __ to the second or ___ gene
recessive, dominant
dominant, recessive
hypostatic, epistatic
epistatic, hypostatic
epistatic, hypostatic
Epistasis describes the interaction of genes, where the epistatic gene masks the effects of another gene, called the hypostatic gene.
Example Question #2 : Understand Epistasis
Which of the following is true?
Epistasis describes the interaction of two alleles
Epistasis describes the interaction of two genes producing a new phenotype
The epistatic locus can suppress the effect of the hypostatic locus
The hypostatic locus masks the effects of the epistatic locus
The epistatic locus can suppress the effect of the hypostatic locus
Epistasis describes the interaction of genes, where the gene at the epistatic locus masks the effects of another gene at the hypostatic locus.
Example Question #3 : Understand Epistasis
In a case of recessive epistasis, A is epistatic to B, and B is dominant to b, which genotype will give the dominant phenotype?
aabb
aaBB
AAbb
AaBb
AaBb
As this is recessive epistasis, only the genotype aa will mask gene B (Aa will not mask B). BB or Bb will give the dominant phenotype as B is dominant to b. Thus, AaBb will yield the dominant phenotype.
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 red snapdragon
bbaa results in yellow snapdragon
bbAa results in yellow 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.
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