Punnett Square Quiz
Questions: 16 · 10 minutes
1. A class models an Aa × Aa cross, which predicts a 3:1 phenotypic ratio under complete dominance. A small set of actual offspring does not match that ratio exactly. What is the best explanation?
The dominant allele must have become recessive
One parent must actually have been AA
Punnett squares give expected probabilities, while small samples can differ through chance
Every group of four offspring must contain exactly three dominant phenotypes
2. A parent has genotype Aa for one gene. Which alleles can this parent contribute through its gametes?
Only A, because it is written first
Either A or a
Aa together in every gamete
AA or aa
3. In the cross Aa × Aa, what is the probability that an offspring will inherit at least one dominant A allele?
1/4
3/4
1/2
1
4. Two Aa parents have already had three children with genotype aa. Assuming each conception is independent, what is the probability that their next child will also have genotype aa?
0%, because three recessive outcomes have already occurred
1/4, because each conception has the same independent probability
3/4, because previous outcomes alter the next cross
1/16, because the same outcome becomes less likely each time
5. For two unlinked genes, an AaBb individual is crossed with an aabb individual. What is the probability of an aabb offspring?
1/4
1/2
3/4
1/16
6. Two heterozygous parents are crossed: Aa × Aa. What is the probability that an offspring will have genotype aa?
0%
50%
25%
75%
7. Assuming independent assortment, which gametes can an AaBb individual produce?
AB, Ab, aB, and ab
AB and ab only
Aa and Bb only
AA, Ab, aB, and bb
8. What is the primary purpose of a Punnett square?
To show the exact traits that every offspring in a family will develop
To display the possible allele combinations offspring may inherit from a genetic cross
To identify the physical location of a gene on a chromosome
To measure how strongly environmental conditions affect a trait
9. In a cross Aa × Aa, allele A is completely dominant over a. What is the expected phenotypic ratio?
Three showing the dominant phenotype to one showing the recessive phenotype
One showing the dominant phenotype to one showing the recessive phenotype
One AA to two Aa to one aa
All showing the dominant phenotype because both parents carry A
10. In the MN blood group, Lᴹ and Lᴺ are codominant. What phenotypes are expected from LᴹLᴺ × LᴺLᴺ?
All M
Three-quarters MN and one-quarter N
Half M and half N
Half MN and half N
11. A plant with a dominant phenotype has an unknown genotype of either AA or Aa. After it is crossed with an aa plant, at least one offspring has the recessive phenotype. Which conclusion is supported?
The unknown plant is homozygous dominant, AA
The aa plant supplied an A allele to that offspring
The unknown plant is heterozygous, Aa
The A allele changed from dominant to recessive during reproduction
12. A carrier mother for an X-linked recessive trait has genotype XᴺXⁿ, and the father is unaffected with genotype XᴺY. What fraction of their sons is expected to express the trait?
None of the sons
One-quarter of the sons
All of the sons
One-half of the sons
13. For a cross between AA and aa parents, what genotype is expected for the offspring?
Half AA and half aa
One-quarter AA, one-half Aa, and one-quarter aa
All Aa
A different genotype in every offspring
14. In snapdragons, RR produces red flowers, rr produces white flowers, and Rr produces pink flowers through incomplete dominance. In an Rr × Rr cross, what is the probability of pink offspring?
25%
75%
100%
50%
15. Which statement correctly distinguishes genotype from phenotype?
Genotype is an observable trait, while phenotype is an allele combination
Genotype is determined by the environment, while phenotype is inherited unchanged
Genotype describes dominant alleles, while phenotype describes only recessive alleles
Genotype is an organism’s allele combination, while phenotype is an observable expression of traits
16. Which is an important limitation of a basic Punnett square?
It does not by itself account for environmental influences on how a trait is expressed
It cannot represent more than one possible offspring genotype
It can be used only when both parents are homozygous
It cannot calculate probabilities for recessive alleles