Week 11 Quiz

A pea plant carries one T allele and one t allele for a gene, where T is dominant. Which description of this plant is accurate?

Select one.

• Genotype Tt; heterozygous; shows the dominant trait
• Genotype Tt; homozygous; shows the dominant trait
• Phenotype Tt; heterozygous; shows the recessive trait
• Genotype Tt; heterozygous; shows a blend of both traits

If an allele is dominant, it must be the most common version of that gene in a population.

True or false.

• True
• False

According to the law of segregation, each parent passes exactly one allele of a gene to each offspring. What happens in the parent's cells that explains this?

Select one.

• Sister chromatids separate in mitosis, so each body cell keeps only one allele
• Homologous chromosomes separate into different cells in meiosis I
• DNA is copied again between meiosis I and meiosis II
• The dominant allele removes the recessive allele before gametes form

Two heterozygous plants are crossed: Tt × Tt. What phenotype ratio do you expect among many offspring?

Select one.

• 1:2:1
• 1:1
• 3:1
• 9:3:3:1

In the cross Tt × Tt, use the product rule to find the probability that an offspring is tt.

Select one.

• 1⁄2
• 1⁄4
• 3⁄4
• 1⁄16

In the coin-toss example (illustrative), two coins stand in for two Tt parents, and 100 flips give 23 TT, 52 Tt, and 25 tt. Which reading of the phenotypes is accurate?

Select one.

• 23 dominant to 77 recessive, because only TT shows the dominant trait
• The phenotype ratio is 23 : 52 : 25, which is about 1:2:1
• 52 dominant to 48 recessive, because only Tt shows the dominant trait
• 75 dominant to 25 recessive, which reduces to 3:1

A plant shows the dominant trait, but its genotype is unknown. In a test cross with a tt plant, a few of the offspring show the recessive trait. What is the unknown plant's genotype?

Select one.

• Tt
• TT
• tt
• It cannot be known from a test cross

Two plants that are both TtYy are crossed, and the two genes sort independently. Select every statement that is true.

Select every option that applies.

• Each parent makes four gamete types: TY, Ty, tY, and ty
• A full Punnett square for this cross has 16 boxes
• The fraction showing both recessive traits is 1⁄16
• The fraction showing both dominant traits is 1⁄16
• Each parent makes only two gamete types

The law of independent assortment says the alleles of different genes go into gametes independently. Which event in meiosis explains this law?

Select one.

• Crossing over in mitosis mixes the genes on each chromosome
• Sister chromatids separate from each other in meiosis I
• Each chromosome pair lines up at random in meiosis I
• Dominant alleles pull other dominant alleles into the same gamete

Two Tt parents have four children, and all four show the dominant trait. Which statement reads this family correctly?

Select one.

• The rule failed, because one of the four children had to show the recessive trait
• One parent must be TT, because no child shows the recessive trait
• The recessive allele must have been lost from both parents in meiosis
• The family fits the rule, because 3:1 describes odds over many offspring, not a promise in four