Genotype Quiz
Questions: 16 · 10 minutes
1. An organism showing a dominant phenotype could have genotype DD or Dd. Under complete dominance, which mating can reveal whether it carries the recessive allele?
Mate it with a confirmed DD individual and compare the offspring
Mate two confirmed dd individuals without including the organism being tested
Pair it with an individual of unknown genotype that also shows the dominant phenotype
Mate it with a confirmed dd individual and observe whether recessive offspring appear
2. Some people carry a particular genotype but do not display its associated phenotype. Which concept describes the proportion of people with the genotype who show the phenotype?
Homozygosity
Independent assortment
Codominance
Penetrance
3. What does an organism’s genotype describe?
Its genetic makeup at one or more loci
Only its visible physical characteristics
The environmental conditions in which it develops
The complete set of traits it acquires during life
4. Which statement about a DNA mutation is most accurate?
It can occur only in reproductive cells
It always causes a visible and harmful trait
It changes phenotype without altering genetic material
It changes genetic sequence, but it may or may not produce an observable phenotype
5. Identical twins can develop measurable differences in traits as they age. Which explanation best fits genotype–phenotype principles?
Identical twins always inherit different alleles at every locus
A shared genotype guarantees identical phenotypes throughout life
Different environments, experiences, and patterns of gene regulation can affect phenotype
Phenotypic differences prove that the twins came from separate zygotes
6. In the standard ABO blood-group model, which allele combination produces the AB phenotype?
One A allele and one B allele
One B allele and one O allele
Two A alleles
Two O alleles
7. Which statement best defines a phenotype?
An observable or measurable trait shaped by genotype and environment
The pair of alleles inherited at a particular locus
Any DNA sequence that never affects a trait
The probability that a particular allele will be inherited
8. A certain allele is associated with greater plant growth in nutrient-rich soil but makes little difference in nutrient-poor soil. What does this pattern illustrate?
The allele is dominant in rich soil and recessive in poor soil
The plants have no genotype because soil controls the trait
The effect of a genotype can depend on the environment
The allele must mutate whenever soil nutrients change
9. In a classical X-linked recessive model, a carrier mother and an unaffected father have a son. What is the probability that the son inherits the recessive condition?
0%
25%
50%
100%
10. Which example is homozygous at the stated locus?
Two copies of the B allele, written BB
One B allele and one b allele, written Bb
Two different variants, written B1 and B2
Only one reported allele, with the second allele unspecified
11. For a gene with alleles A and a, two heterozygous parents (Aa × Aa) have offspring. What is the probability that an offspring will have genotype aa?
0%
50%
25%
75%
12. Under complete dominance, an individual shows the dominant phenotype for a gene with alleles A and a. What can be inferred from the phenotype alone?
Only the homozygous dominant genotype AA is possible
Either the homozygous genotype AA or the heterozygous genotype Aa is possible
The recessive genotype aa is the only possible genotype
The heterozygous genotype Aa is certain
13. How is an allele related to a gene?
An allele is an observable trait, while a gene is always hidden
An allele is a version of a gene found at a particular locus
An allele is the environmental factor that activates a gene
An allele is a complete chromosome containing many organisms
14. In a population meeting Hardy–Weinberg assumptions, the frequency of recessive allele a is q = 0.20. What is the expected frequency of genotype aa?
0.20, because genotype frequency always equals allele frequency
0.04, because aa has an expected frequency of q squared
0.32, because heterozygotes have an expected frequency of 2pq
0.80, because p equals 1 minus q
15. Two genetically identical plants grow to different heights after one receives less light. What best explains the difference?
Their genotypes must have changed because their heights differ
Environmental conditions influenced how their shared genotype was expressed
Height cannot be considered a phenotype
Each plant must have inherited different alleles from its parents
16. A trait is described as dominant under a simple Mendelian model. What can be concluded from that description alone?
The trait must be common in the population
The trait must improve survival or reproduction
Every child of an affected parent must show the trait
One copy of the dominant allele is sufficient to produce the defined phenotype