Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

According to the law of dominance, what happens in a pair of alleles?

1. Both alleles express equally

2. One allele can mask the other

3. Alleles are passed on independently

4. Neither allele is expressed

The correct answer is: One allele can mask the other

The law of dominance states that in a pair of alleles, one allele can dominate or mask the expression of the other allele when it comes to a particular trait. This means that when an individual carries two different alleles for a trait (heterozygous), it is the dominant allele that determines the phenotype, or observable characteristics, while the recessive allele does not manifest in the phenotype. For instance, if you consider a flower color trait where the allele for red flowers is dominant (R) and the allele for white flowers is recessive (r), a plant with the genotype Rr will express the red flower color, overshadowing the effect of the white allele. This principle is foundational in understanding Mendelian genetics and how traits are inherited, illustrating that dominance is a key factor in how traits are expressed in offspring.