Chapter 10, Problem 1PDT

Summary Introduction

To determine: Whether the populations of both asexually and sexually reproducing organisms will become “completely sexual or asexual”.

Introduction: Various organisms have different methods of reproduction. There are, however, two broad modes of reproduction. The first is asexual reproduction, and the second is sexual reproduction. In the case of asexual reproduction, the organism does not exchange the nuclear material, and the progeny produced is the exact clone of the parent organism. In sexual reproduction, there is exchange of gametes, resulting in variation between species.

Explanation of Solution

No, the organisms that reproduce their progeny both sexually and asexually will not become completely sexual or asexual because both these types have their own merits and demerits. Both are essential for the propagation of generation due to environmental factors; that is why natural selection has not wiped out one of their modes of reproduction.

Asexual reproduction consumes less energy, less time, and fewer resources of the organism. There is no need for distinct reproductive organs, and a large number of individuals can be formed. Also, the rarity of male partners is not a problem for them. Small numbers of gametes are formed, but the most important distinction is “reproductive insurance”. For sexual-reproducing organisms of the size of 100, there are only 50 partners each male and female. However, for an asexual- reproducing population, all the 100 members are available. Also, sexual-reproducing organisms will require some growing period when their sexual organs are developing, but asexual-reproducing organisms, on the other hand, can multiply their numbers generation by generation exponentially.

There are, on the other hand, its own merits such as the selection of favorable traits, variation. Asexual-reproducing organisms have benefits for adaptation with a change in the environment due to which they can survive through the process of natural selection, selective interference, recombination, and mutations. They play an important role in the evolution of new genes, sexual selection, and maintaining vigor to fight inbreeding depression.

These organisms have better adaptations, new characters, and maintain their vigor through a sexual mode of reproduction on one hand. They ensure the survival of ample population size by reproductive insurance, frequent reproduction, and expand their numbers exponentially in less resource and time on the other hand. Hence, these organisms cannot choose one of the alternatives to survive.

Summary Introduction

To determine: The factors that help in maintaining both the modes of reproduction.

Introduction: Various organisms have different methods of reproduction. There are, however, two broad modes of reproduction. The first is asexual reproduction, and the second is sexual reproduction. In the case of asexual reproduction, the organism does not exchange the nuclear material, and the progeny produced is the exact clone of the parent organism. In sexual reproduction, there is exchange of gametes, resulting in variation between species.

Explanation of Solution

The factors that help to maintain sexual reproduction within a population are as follows:

• Presence of selective interference.
• Integration of adaptations into genetic material.
• Acquisition of characters.
• Maintenance and rejuvenation of vigor by removing inbreeding depression.
• Generating variations and positive mutations.
• Survival in natural selection.
• Recombination of nuclear material.

The factors that help to maintain asexual reproduction within a population are as follows:

• Reproductive insurance where every member can reproduce instead of half of the population as in sexual-reproducing organism.
• Takes minimal amount of time and quick process for increasing population size; does not take a long time in the maturation of sexual organs.
• No distinct organs are required for reproduction.
• Less expenditure on energy and resources.
• The process of mating is not required in asexual reproduction. It does not require the formation of a large number of gametes for successful fertilization.

Summary Introduction

To determine: Importance of organisms such as fish, insects, and crustaceans in the study of the factors that maintain sexual reproduction.

Introduction: Various organisms have different methods of reproduction. There are, however, two broad modes of reproduction. The first is asexual reproduction, and the second is sexual reproduction. In the case of asexual reproduction, the organism does not exchange the nuclear material, and the progeny produced is the exact clone of the parent organism. In sexual reproduction, there is exchange of gametes, resulting in variation between species.

Explanation of Solution

Organisms such as fish, insects, and crustaceans provide a critical framework for evolutionary studies. Their genetic composition has provided a lot of information about how this group of organisms transformed into other organisms. There are a number of evidences that reveal about the importance of sexual reproduction in these groups. The evolution of new characters is a very complex and incredibly a slower process but a changing environment increases the rate of variation among the member of species. Hence, sexual reproduction is also affected by the changing environmental conditions. These organisms provide information regarding evolutionary process that has occurred during millions of years.

These organisms provided a lineage of genes associated with their species. They have also provided critical information about the factors and conditions that were involved in their adaptation to the changing environment. These changes were the result of the variation for maximizing their fitness for the survival in the new environment. They project framework of the evolution of a single organism into new forms.. The difference in gene and genetic content helps one to know how organisms changed and adapted to the new environment.

Some of the examples of the importance of these animals for these factors are as follows:

• Loss of expression to reduce the size of pelvic girdle in three-spine stickleback fish.
• Mutations in the Hox gene of Drosophila melanogaster helped the evolution of the antennae into legs.

The main factors responsible for maintaining sexual reproduction in these organisms are:

• The changes required for adjustment to the new environment is caused by the exchange of genetic material and variation by meiosis and fertilization events of the sexual reproduction.
• The limitation of resources in an environment forces organism to shift to the new energy source and the development of pathways for the utilization of that source is only possible by variations.
• The increased competition with the member of the species forces member of species, to be fit and acquisition of novel trait by sexual reproduction leads to the increase of the overall fitness.
• The increase in competition with the members of the other species for resources and area can result in the quest for survival and development of new strategies or migration of the population towards new area both requires adaptation which inculcates with the help of sexual reproduction.