9.1.2 Mendel's Findings: A First Look at Phenotypic Ratios Flashcards
Gregor Mendel
- was one of the first scientists to use mathematical analysis in a quantitative experiment.
three generations
- Mendel conducted his experiments in three generations: the (P) parent generation, (F1) first filial generation, and (F2) second filial generation. He examined seven traits of true-breeding pea plants, each having two alternate forms for a single trait.
• When alternate forms of a single trait were crossed, one of the forms disappeared in the F1 generation, and then reappeared in the F2 generation.
• The form of the trait that masks other traits is called the dominant trait. The dominant and masked traits appear in the F2 generation in a 3:1 ratio.
note
- In preparing for his experiments, Mendel bought 34
true-breeding seed varieties. True-breeding plants are strains that contain only one form of a trait. Of the 34 varieties, Mendel chose only seven to use in his experiments. Then he performed crosses in plants that varied in a single trait. - In the experiment on the left, the trait is flower color. A
true-breeding yellow flower was crossed with a true-breeding green flower. Reciprocal crosses with male and female flowers were performed as a control. - The initial cross between the true-breeding individuals is called the (P) parental cross. Offspring that result from the cross are called the (F1) first filial generation. When the F1 generation is crossed, the resulting offspring are called the (F2) second filial generation.
- In the experiment on the left, Mendel crossed true-breeding wrinkled-seed plants with true-breeding smooth-seed plants. The F1 generation consisted entirely of smooth-seed plants. The F2 generation contained smooth and wrinkled seeds. Instead of merely observing that both types were present, Mendel counted the ratio of smooth to wrinkled seeds. He
determined that 3/4 were smooth and 1/4 were wrinkled. - Mendel’s results showed that the wrinkled trait disappeared in the F1 generation and reappeared in the F2 1/4 of the time.
Mendel hypothesized that traits did not blend together like paint but were particulate. At what part of the experiment could Mendel rule out the blending mode of inheritance?
- At the F2, when the masked variety reappeared
Mendel used pea plants for his experiments for all of the following reasons except which of the following?
- The characters varied over a continuous range of phenotypes
If Mendel had produced from his crosses (using the wrinkled and smooth seed-coat trait) 1425 pea seeds in the F2 generation, how many would you expect to be wrinkled?
- 355
Mendel’s primary experiments were conducted with
- pea plants
Which one of the following is not true of Mendel’s parental cross?
- His results indicated a ratio in the offspring of 3:1
Which one of the following is not one of the reasons that Mendel succeeded in determining the principles of inheritance?
- He followed the inheritance pattern of many traits at the same time
Which of the following best describes a reciprocal cross?
- Pollen from plant “A” is transferred to plant “B”, and pollen from plant “B” is transferred to plant “A”.
Genetic studies in the 1900s often used the fruit fly as a model. Why did early studies of inheritance in the 1700s and 1800s use plants?
- Plants are inexpensive to grow.
- Plants are easy to manipulate.
- True breeding plant strains were readily available.
Which one of the following best describes a monohybrid cross?
- Plants that differ in a single trait are cross-pollinated with each other
A true-breeding strain is one that
- produces offspring of the same variety when they self-pollinate
To investigate patterns of inheritance, Mendel looked at traits that
- were dichotomous in nature.
