Chapter 10, Problem 12A

Summary Introduction

To explain:

The differences between the given vocabulary terms

Introduction:

The study of heredity is called genetics. Gregor Mendel was a mathematician who studied how some characteristics are passed from parent to offspring while others do not. Heredity is passing on of characteristics from parent to offspring. These characteristics are known as traits.

Answer to Problem 12A

Dominant	Recessive
Trait of an organism that is visible.	Trait of an organism that is masked.
The allele for dominant trait will be expressed if it is present.	The allele for recessive trait will be expressed if dominant allele is absent.
It masks or cover ups the recessive trait.	It cannot mask the dominant trait.

Explanation of Solution

When Mendel performed experiments on garden peas, he found that the seeds of peas carried the traits of the plants between which pollination occurred. He cross pollinated many plants and found that the seeds had traits of two different plants. He produced hybrids of plants which had different forms of a trait such as tall and dwarf plants.

Each organism has two factors for each trait. These factors are called genes. Each gene has two alternative forms called alleles. For example there are two alleles for height; tall and short. A plant can have two alleles for tallness or two alleles for shortness or one for tallness and one for shortness. The organism receives one allele from the female parent and one from the male parent.

When a tall plant was crossed with a dwarf plant, he found that all plants in the first generation were tall. The trait for tallness was clearly visible while the trait for dwarfness was masked. The observed trait is known as dominant trait while the masked trait is called recessive trait.

A dominant trait will always mask or cover up the recessive trait. The allele for tallness is dominant to the allele for shortness. The plants that had a tall and short allele were also tall because the tall allele is dominant. Plants with two alleles for tallness were tall and plants with two alleles for shortness were short. In the F₁generation of plants, each plant had one tall allele and one short allele. That is why they were all tall.