Chapter 13, Problem 7A

Summary Introduction

To discuss:

The advantages and disadvantages of selective breeding.

Introduction:

The process by which desired traits of certain plants and animals are selected and passed on to their future generations is called selective breeding. This can be achieved through hybridization and inbreeding. It increased the frequency of desired allele within a population.

Answer to Problem 7A

Advantages of selective breeding:

Increases food production

Hybrids have better adaptability to changes in the environment

Produce large number of offspring

Hybrids have desired traits

Inbreeding helps in maintaining pure breeds

Disadvantages of selective breeding:

Hybridization is time consuming

Expensive Inbreeding causes loss of variation

Harmful recessive traits can be passed on to future generations

Explanation of Solution

Advantages of selective breeding:

Increases food production- Hybrid plants can be bred to be more nutritious, disease resistant and bear large fruits. Many crop plants like maize, wheat, rice and garden flowers are produced by hybridization. High yielding varieties have been developed to decrease food shortage.

Hybrids have better adaptability to changes in the environment- The selected traits give hybrids a competitive edge and a better ability to adapt to the changes in the environment as they are stronger and disease resistant. The offspring produced by crossing two pure breed plants are often stronger and larger than their parent plants.

Produce large number of offspring- Hybridization results in production of large number of offspring.

Hybrids have desired traits- Organisms with desired traits can be produced by crossing parent organisms with different forms of a trait.

Inbreeding helps in maintaining pure breeds- Pure breeds can be maintained by inbreeding as it results in offspring that are homozygous for most traits. Augus cattle and German shepherd dogs are examples of organisms produced by inbreeding.

Disadvantages of selective breeding:

Hybridization is time consuming- It took rice breeders three decades to produce high yielding hybrid rice variety. Selective breeding requires time, patience and several generations of offspring before the desired trait becomes common in a population.

Expensive- Since several hybrids are to be produced and tested, the entire process is very expensive.

Inbreeding causes loss of variation- During inbreeding the undesired traits are eliminated. It leads to loss of variation in characters over the generations.

Harmful recessive traits can be passed on to future generations- Inbreeding increases the chances of homozygous recessive offspring. So if both parents carry the recessive allele, the harmful trait will not get eliminated and will be expressed in future generations.