Mendelian Genetics Quiz
Questions: 16 · 10 minutes
1. Assuming independent assortment, what is the probability of an aabb offspring from the cross AaBb × aabb?
1/4
1/2
3/4
1/16
2. Under a simple Mendelian model, two unaffected parents have an affected daughter. Which inheritance pattern is most consistent if the trait is rare and neither parent has the phenotype?
Y-linked inheritance
Autosomal recessive inheritance
Autosomal dominant inheritance
Mitochondrial inheritance from an affected mother
3. A dihybrid testcross produces far more offspring with parental allele combinations than with recombinant combinations. What is the best explanation?
Both traits display incomplete dominance.
Allele segregation failed during every instance of gamete formation.
The two recessive alleles cannot occur in the same gamete.
The genes are linked on the same chromosome.
4. If an AaBb individual forms gametes and the genes assort independently, which list includes every possible allele combination in its gametes?
AA, Aa, BB, Bb
A, a, B, b
AB, Ab, aB, ab
Aa, Ab, aB, Bb
5. What occurs in codominance?
The heterozygote has a phenotype midway between those of the two homozygotes.
One allele permanently changes the DNA sequence of the other allele.
Both alleles are distinctly expressed in the heterozygote.
Each allele is expressed in a different generation.
6. Which conditions support an expected 3:1 phenotypic ratio in the offspring?
A homozygous dominant parent crossed with a homozygous recessive parent
One gene with complete dominance, with both parents heterozygous
Two independently assorting genes examined in a testcross
One gene with codominant alleles, with both parents homozygous
7. For a gene whose alleles are represented by G and g, which option is a heterozygous genotype?
GG, containing two dominant alleles
Gg, containing two different alleles
gg, containing two recessive alleles
A gamete carrying only the G allele
8. How does incomplete dominance differ from complete dominance?
Neither allele contributes to the heterozygote’s phenotype.
The heterozygote has an intermediate phenotype instead of matching either homozygote.
The recessive allele prevents the dominant allele from entering gametes.
The heterozygote always matches the dominant homozygote.
9. Purple flower color is dominant to white. A purple-flowered plant of unknown genotype is crossed with a white-flowered plant, pp, and at least one white offspring appears. What must the purple parent’s genotype be?
PP, because the parent has two dominant alleles
pp, because white offspring require recessive alleles
Either PP or Pp, because both produce purple flowers
Pp, because the parent must carry a recessive p allele
10. Two heterozygous parents, Aa × Aa, plan for two offspring. Assuming independent outcomes, what is the probability that both offspring will have genotype aa?
1/2
1/8
1/4
1/16
11. Mendel’s law of independent assortment most directly predicts independent inheritance under which condition?
The two symbols represent alternative alleles at the same locus.
Both traits are controlled by dominant alleles.
The genes are unlinked, as genes on different chromosomes generally are.
The genes are expressed only in haploid organisms.
12. In a cross between two heterozygous parents, Aa × Aa, what is the probability of an aa offspring?
1/4
1/2
0
3/4
13. In peas, round seeds are dominant to wrinkled seeds. What genotype must a wrinkled-seed plant have?
rr, with two recessive alleles
Rr, with one dominant and one recessive allele
Either RR or Rr, since both include a dominant allele
RR, with two dominant alleles
14. Which statement best describes Mendel’s law of segregation?
Genes located on the same chromosome must always enter different gametes.
Dominant alleles automatically become more common with each generation.
The two alleles of a gene separate during gamete formation, so each gamete receives one allele.
An offspring receives both alleles of every gene from a single parent.
15. With complete dominance, what proportion of offspring from Aa × aa is expected to show the dominant phenotype?
All offspring
1/4
3/4
1/2
16. A plant has a dominant phenotype, but its genotype could be AA or Aa. Which cross is most useful for determining its genotype?
Cross it with a homozygous recessive individual, aa.
Cross it with another individual showing the dominant phenotype.
Cross it with an individual whose genotype is unknown.
Cross it with a known homozygous dominant individual, AA.