9.1.3 Mendel's Conclusions: Alternate Alleles and Dominance

Question 1

note

Answer 1

• After analyzing his results, Mendel concluded that alternate versions of heritable factors exist.
  • The factors are now called genes, and the alternate versions are called alleles.
  • For his work with pea plants, Mendel hypothesized:
  · The factors (genes) consist of pairs of alternate forms (alleles).
  · Each trait was controlled by a pair of alleles
• After analyzing his results, Mendel concluded that alternate versions of heritable factors exist. We now call the heritable factors genes. The alternate forms of a gene are called alleles. Mendel proposed that each parent contributes only one allele of its pair to the offspring. Analyzing his results mathematically helped him to substantiate his theory.
• Mendel was ahead of his time; he discovered the processes of meiosis before the chromosome theory was developed. Pairs of alleles segregate during gamete formation. In combination, one allele may dominate or mask the other.
• Mendel concluded that when the alleles occurred together in a plant, the smooth-seed trait dominates the wrinkled-seed trait. The trait that is masked is called the recessive trait.

Question 2

law of segregation

Answer 2

• According to the law of segregation, the pairs segregate and each parent donates only one to the offspring.

Question 3

review

Answer 3

• When Mendel crossed true-breeding wrinkled-seed
  plants with smooth-seed plants, all of the F1 plants had smooth seeds. The wrinkled trait reappeared in the F2
  in a 1:3 ratio with the smooth trait

Question 4

When a true breeding smooth-seeded pea plant is crossed with one that is a true breeding wrinkled seeded pea plant, why is a wrinkled-seeded offspring unlikely to result?

Answer 4

• The smooth-seeded gene masks the wrinkled-seeded gene in the F1 generation.

Question 5

Mendel found that monohybrid crosses of true-breeding plants that differ in one trait always produced F1 offspring of the same variety. This variety of the trait is considered

Answer 5

• dominant

Question 6

From his experimental results, Mendel developed a hypothesis that is now called the first law of segregation. Which of the following is not a part of this hypothesis?

Answer 6

• Every organism gets two copies of a gene from each parent

Question 7

In pea plants, plants with inflated pods are crossed with ones with constricted pods. All of the offspring are found to have inflated pods. If a cross is carried out among the offspring, what would be the expected ratio for the phenotypes of the F2 generation?

Answer 7

• Three inflated to one constricted

Question 8

According to Mendel’s model, which of the following is the best explanation for a given trait disappearing for a generation?

Answer 8

• Dominant alleles mask recessive alleles

Question 9

Which one of the following best illustrates alleles of a gene?

Answer 9

• A gene for green pods and a gene for yellow pods

Question 10

A pea plant with green pods is crossed with a pea plant with yellow pods. The F1 generation was all the same color. If 75% of the F2 generation have green pods and 25% have yellow pods, what conclusion can we make?

Answer 10

• Both parent plants were true breeding

Question 11

Let S be the allele for smooth seeds and s be the allele for wrinkled seeds. If an individual has the allelic combination Ss, which of the following is a true statement concerning this individual?

Answer 11

• The individual has smooth seeds

Question 12

Which of the following Mendelian conclusions describes the process of meiosis?

Answer 12

• Alleles are segregated in the formation of gametes

Question 13

“Segregation” of alleles means:

Answer 13

• the separation of alleles during the formation of gametes

Question 14

Which of the following is not true of Mendel’s mechanism of inheritance?

Answer 14

• Heritable factors that are dominant are more likely to be passed on to the next generation.