Multiple Choice
Which of the following of Mendel's laws states that two alleles for a single gene separate during gamete formation?
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17. Meiosis and Sexual Reproduction
Mendel and the Laws of Inheritance
Multiple Choice
In the context of Mendelian inheritance patterns, why is sickle-cell anemia often cited as an example of codominance?
A
The HbS allele is located on mitochondrial DNA, so it does not follow Mendel’s laws.
B
Heterozygotes (HbA/HbS) produce both normal hemoglobin (HbA) and sickle hemoglobin (HbS), so both alleles are expressed in the phenotype.
C
Heterozygotes (HbA/HbS) express an intermediate hemoglobin type that blends HbA and HbS into a single new form.
D
Only the HbS allele is expressed in heterozygotes (HbA/HbS), completely masking HbA.
Verified step by step guidance1
Understand the concept of codominance: In codominance, both alleles in a heterozygote are fully expressed, resulting in a phenotype that shows both traits simultaneously without blending.
Recall the genetic basis of sickle-cell anemia: The HbA allele codes for normal hemoglobin, while the HbS allele codes for sickle hemoglobin, a variant that causes red blood cells to deform under low oxygen conditions.
Analyze the heterozygous genotype (HbA/HbS): Individuals with this genotype produce both normal hemoglobin (HbA) and sickle hemoglobin (HbS) because both alleles are active and expressed.
Contrast codominance with incomplete dominance: Unlike incomplete dominance, where heterozygotes show an intermediate phenotype blending both alleles, codominance results in the presence of both distinct forms of hemoglobin in the phenotype.
Conclude why sickle-cell anemia is an example of codominance: Since heterozygotes express both HbA and HbS proteins simultaneously, the condition exemplifies codominance rather than dominance or incomplete dominance.
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