Week 12 Quiz

A gardener crosses a red snapdragon with a white snapdragon, and every offspring has pink flowers. Which inheritance pattern does the pink heterozygote show?

Select one.

• Codominance, because both colors appear side by side on each petal
• Incomplete dominance, because the heterozygote is a blend between the parents
• Complete dominance, because pink hides both red and white
• Multiple alleles, because the population holds three different flower colors at once

Two pink snapdragons (RW × RW) are crossed. Which phenotype ratio do you expect among their offspring?

Select one.

• 3 pink : 1 white
• 1 pink : 1 white
• 1 red : 2 pink : 1 white
• 3 red : 1 white

A person with type AB blood has red blood cells that carry both the A antigen and the B antigen in full, which is an example of codominance.

True or false.

• True
• False

Type O is a common blood type. Which statement explains why?

Select one.

• The i allele is dominant to both Iᴬ and Iᴮ, so it shows whenever present
• The i allele is common in the population, although it is recessive
• Type O is the heterozygote of the A and B alleles
• Type O is a blend of the A antigen and the B antigen on each cell

A parent with type A blood (Iᴬi) and a parent with type B blood (Iᴮi) have a child. What is the probability that the child has type O blood?

Select one.

• 1⁄2
• 0
• 3⁄4
• 1⁄4

A carrier mother (XᴬXᵃ) and an unaffected father (XᴬY) have children. For an X-linked recessive trait, which description of their daughters is accurate?

Select one.

• None of the daughters are affected, and half of them are carriers
• Half of the daughters are affected, like half of the sons
• All of the daughters are carriers, and none is affected
• A quarter of the daughters are affected, and the rest are unaffected carriers

A son shows an X-linked recessive trait, and neither of his parents shows it. From which parent did he receive the recessive allele?

Select one.

• From his father, who gave him his X chromosome
• From both parents equally, one copy of the allele from each of them
• From his father, who is a male carrier
• From his mother, who gave him his X chromosome

Which statements about X-linked recessive inheritance are accurate? Select all that apply.

Select every option that applies.

• A male with one recessive allele on his X shows the trait
• A male can carry the allele without showing the trait
• Such traits are far more common in males than in females
• A female shows the trait only with the recessive allele on both X chromosomes
• The recessive allele rides on the Y chromosome

In a cross of two double heterozygotes, the two genes sit close together on the same chromosome. How do these linked genes change the result you would expect from independent assortment?

Select one.

• They tend to travel together, so the cross does not give 9:3:3:1
• They assort independently, so the cross still gives 9:3:3:1
• They always separate in crossing over, so every class is equal
• They blend into one single gene, so the cross gives a 3:1 ratio of offspring

A pedigree shows an unaffected couple in generation I with three children in generation II: one affected son and two unaffected daughters. Which reading follows the two decisions in order?

Select one.

• Dominant, because a shaded symbol appears in generation II
• Recessive and X-linked, with the father as the carrier
• Recessive and consistent with X-linked, with the mother as an obligate carrier
• Dominant and autosomal, because only one of the three children in generation II is affected