Most Missed Genetics Questions

In pea plants, the allele for tall stems is dominant over the allele for short stems. If two heterozygous tall plants are crossed, what percentage of the offspring would be expected to have the same phenotype as the parents?

• 25%

• 50%

• 75%

• 100%

Answer explanation

Heterozygous means two different alleles (Tt x Tt)

A trait for petal color in snapdragon flowers has two alleles, white and red, that demonstrate incomplete dominance.  If one white and one red individual are crossed, what percentage of their offspring is LIKELY to have pink petals?

• 25%

• 50%

• 75%

• 100%

Answer explanation

White (WW) crossed with red (RR)

Lisa learned that blue eye color is a recessive trait and brown eye color is a dominant trait. Lisa and her sister, Sara, both have blue eyes. Her parents, Joan and Greg, both have brown eyes. Lisa drew her family pedigree, beginning with both sets of grandparents. Which statement is TRUE?

• Blue eye color is expressed in every other generation (skips a generation)

• Both parents have a gene for blue eyes but it is not expressed (shown)

• The grandparents' genes for eye color are not influencing Lisa and her sister's genes for eye color

• Eye color is not a hereditary trait, so the girls did not get their eye color from their parents

Answer explanation

The parents have BROWN eyes, but Sara and Lisa both have BLUE eyes. This means that both their parents are heterozygous (Bb x Bb). The girls had a 25% chance of getting blue eyes (bb).

Unattached earlobes are controlled by a dominant allele, E, while attached earlobes are controlled by a recessive allele, e. If a homozygous dominant individual for unattached earlobes mates with a heterozygous dominant individual for unattached earlobes, which statement is correct about their possible offspring?

• Their offspring have 100% chance of having unattached earlobes

• Their offspring have 0% chance of having unattached earlobes

• Their offspring have 25% chance of having attached earlobes

• Their offspring have 75% chance of having attached earlobes

Answer explanation

Homozygous dominant (EE) x heterozygous dominant (Ee)

The allele for tall pea plants is dominant over the allele for short pea plants. In a cross between a homozygous tall pea plant and a short pea plant, what are the possible phenotypes of the offspring?

• 100% tall

• 100% short

• 50% tall and 50% short

• 75% tall and 25% short

Answer explanation

Homozygous tall (TT) crossed with short (tt)

If Mr. and Mrs. Johnson had four children together, what color of hair would the children likely have?

• All 4 of the children would have black hair

• Only 3 of the children would have black hair and 1 child would have blond hair

• All 4 of the children would have blond hair

• Only 2 of the children would have black hair, and 2 of the children would have blond hair

Answer explanation

Mr. Johnson is homozygous for black hair (BB) and Mrs. Johnson is homozygous for blond hair (bb).

Some people are able to roll their tongues into a U-shape. The ability to do this is inherited as a dominant allele. What is the probability that children from two heterozygous parents will be able to form a U-shaped tongue?

• 25%

• 50%

• 75%

• 100%

Answer explanation

Heterozygous is two different alleles (Rr x Rr)

For a particular trait, B is dominant to b. Which of the following genetic crosses would be expected to result in 50% of the offspring showing the phenotype of the dominant allele and 50% showing the phenotype of the recessive allele?

• BB x Bb

• Bb x Bb

• Bb x bb

• bb x bb

Answer explanation

MAKE A PUNNET SQUARE FOR EACH POSSIBILITY

The pedigree shows hair color. In this pedigree, light hair color is the recessive allele and dark hair color is the dominant allele. Which Punnett square shows the possible genotypes for offspring Z's hair color?

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• 
• 
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Answer explanation

Dark hair (D) is dominant to light hair (d). Z's dad has dark hair and Z's mom has light hair. This means that Z's mom has to be (dd). In order for Z's sisters to have both light and dark hair, dad HAS to be heterozgous (Dd)

Mitchell is interested in the snapdragons that reproduce sexually. He knows that purple (P) is dominant to white (w). Mitchell crosses a homozygous purple plant with a homozygous white plant.

If he breeds two of the first generation offspring together, what percentage of the second generation offspring can Mitchell predict will most likely be white?

• 25%

• 50%

• 75%

• 100%

Answer explanation

First you have to make a Punnett square between homozygous purple (PP) and homozygous white (ww). All of that first generation will be purple (Pw). THEN you have to make a SECOND PUNNETT SQUARE between (Pw x Pw) to find the SECOND GENERATION percent.