Multiple Choice
In a population of 100 individuals, where each individual has two alleles for a gene, and 40 individuals are homozygous for the 'b' allele, what is the total number of 'b' alleles in the population?
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12. Meiosis
Genes & Alleles
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Which of the following best describes a recessive allele?
A
An allele that determines the phenotype in a heterozygous condition
B
An allele that is expressed only in the presence of a dominant allele
C
An allele that is always expressed regardless of other alleles
D
An allele that is expressed only when two copies are present
Verified step by step guidance1
Understand the concept of alleles: Alleles are different forms of a gene that can exist at a specific locus on a chromosome. They can be dominant or recessive.
Define a recessive allele: A recessive allele is one that is not expressed in the phenotype unless two copies are present, meaning the organism is homozygous recessive.
Contrast with dominant alleles: Dominant alleles are expressed in the phenotype even if only one copy is present, meaning the organism can be heterozygous.
Consider heterozygous vs. homozygous conditions: In a heterozygous condition, one dominant and one recessive allele are present, and the dominant allele determines the phenotype. In a homozygous recessive condition, two recessive alleles are present, and the recessive trait is expressed.
Apply this understanding to the options: The correct description of a recessive allele is that it is expressed only when two copies are present, which aligns with the definition of a recessive allele being expressed in a homozygous recessive condition.
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