Punnett Squares
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Middle School Life Science › Punnett Squares
In butterflies, the gene for black wings (B) is dominant to the gene for blue wings (b). For which of the following parental genotypes would 100% of offspring be expected to be blue?
Bb x Bb
BB x bb
bb x bb
BB x BB
Explanation
The answer is "bb x bb" because in all the other scenarios, the black gene would be dominant over the blue gene in at least one offspring.
Brown fur is dominant to white fur in a species of rabbit and is represented with the alleles "B" and "b".
What are the resulting percentages of genotypes of a cross between a homozygous dominant parent and a heterozygous parent?
50% BB and 50% Bb
75% BB and 25% Bb
50% BB, 25% Bb, 25% bb
100% BB
Explanation
The answer is 50% BB and 50% Bb, as shown in the punnet square below. The phrase "homozygous dominant" means the genotype of one parent is BB while "heterozygous" is a genotype of Bb.
In butterflies, the gene for black wings (B) is dominant to the gene for blue wings (b). For which of the following parental genotypes would 100% of offspring be expected to be blue?
Bb x Bb
BB x bb
bb x bb
BB x BB
Explanation
The answer is "bb x bb" because in all the other scenarios, the black gene would be dominant over the blue gene in at least one offspring.
Brown fur is dominant to white fur in a species of rabbit and is represented with the alleles "B" and "b".
What are the resulting percentages of genotypes of a cross between a homozygous dominant parent and a heterozygous parent?
50% BB and 50% Bb
75% BB and 25% Bb
50% BB, 25% Bb, 25% bb
100% BB
Explanation
The answer is 50% BB and 50% Bb, as shown in the punnet square below. The phrase "homozygous dominant" means the genotype of one parent is BB while "heterozygous" is a genotype of Bb.
The allele for black feet in a species of duck is dominant to the allele for brown feet. What are the phenotypes of the offspring from the cross shown in the punnet square above?
75% black feet and 25% brown feet
25% black feet and 75% brown feet
25% BB, 25% bb, and 50% Bb
75% B and 25% b
Explanation
The answer is "75% black feet and 25% brown feet" because phenotypes are the physical expression of an allele pair and the dominant allele for black feet will overpower the allele for brown feet.
The allele for black feet in a species of duck is dominant to the allele for brown feet. What are the phenotypes of the offspring from the cross shown in the punnet square above?
75% black feet and 25% brown feet
25% black feet and 75% brown feet
25% BB, 25% bb, and 50% Bb
75% B and 25% b
Explanation
The answer is "75% black feet and 25% brown feet" because phenotypes are the physical expression of an allele pair and the dominant allele for black feet will overpower the allele for brown feet.
In poodles, the allele for black fur (B) is dominant to the gene for brown fur (b). Two poodles are crossed. One poodle is homozygous for black fur, and the other is heterozygous. What percentage of the offspring are expected to have black fur?
100%
75%
50%
25%
0%
Explanation
The answer is 100%. All offspring are expected to have black fur because all offspring will have at least one dominant allele for black fur which will overpower any allele for brown fur.
In poodles, the allele for black fur (B) is dominant to the gene for brown fur (b). Two poodles are crossed. One poodle is homozygous for black fur, and the other is heterozygous. What percentage of the offspring are expected to have black fur?
100%
75%
50%
25%
0%
Explanation
The answer is 100%. All offspring are expected to have black fur because all offspring will have at least one dominant allele for black fur which will overpower any allele for brown fur.
Polycystic Kidney Disease (PKD) is a disease that can cause kidney failure. This disease is usually caused by a dominant allele. What is the chance that a child will have PKD if the father is unaffected and the mother is heterozygous for PKD?
100%
75%
50%
25%
0%
Explanation
The answer is "50%."
The allele for blue eyes is "t" while the allele for brown eyes is "T". What percentage of offspring produced by two parents with blue eyes would also have blue eyes?
100%
50%
25%
0%
Explanation
The answer is 100%. Since both parents had to have homozygous recessive alleles for blue eyes in order to express them, they both must have "tt" for a genotype. The following punnet square shows the results.
