REPRODUCTION AND TYPES OF REPRODUCTION

REPRODUCTION

REPRODUCTION:

        The process in which living organisms produce individuals of the same kind to continue its generation is called reproduction.

(i) It is a natural device developed by all living organisms.

(ii) A species cannot survive without reproduction i.e. essential to continue its generation.

(iii) The genetic material shifts to the next generation through reproduction.

Types of reproduction:

       Reproduction occurs by two major types;

 Asexual reproduction and Sexual reproduction.

1) Asexual reproduction:

        Asexual reproduction means simple cells division, produced from a single parent.

(i) The resulting offspring are genetically similar to the parent.

(ii) No genetic variations occur in this type of reproduction.

(iii) An economical method used for new organisms.

iv) A quick and shortcut method.

(v) No new variety is produced.

 2) Sexual reproduction:

          Sexual reproduction involves fusion of male and female sex cells called gametes. Fusion of sperms and egg cells Is called fertilization.

         The new cell which is formed by fertilization is called a zygote. The zygote divides again and again until grows into a new organism. The new organisms produced by sexual reproduction are not identical to each other or to their parents. They contain different combinations of genes.

Number of chromosomes in sex cells and body cells:

         Gametes or sex cells are different from body cells, also called somatic cells. In humans, there are 46 chromosomes in each of their body cells. But there are 23 chromosomes in sperm cells and 25 chromosomes in egg cells.

         At fertilization, when sperm fuses with the eggs, the zygote formed has 46 chromosomes. It is called 2N or diploid number of chromosomes. Sperm or egg, each contain haploid, 1N (23) chromosomes. Sex cells or gametes are always haploid when two gametes fuse together, they form a diploid zygote.

Methods of asexual reproduction;

Binary fission

Budding

Spore formation

Asexual reproduction:

          There are many types of asexual reproduction. Individuals produced by asexual methods are genetically identical. Asexual reproduction occurs by the following different mechanisms in different organisms such as:

a) Binary fission

b) Budding

c) Spore formation

a) Binary fission:

         Binary fission means "division into two". In this type of asexual reproduction, body of parent organism divides into two daughter organisms. This process of binary fission is found in Amoeba, Euglena, Chlamydomonas and Bacteria.

         In bacteria, binary fission takes place during favorable conditions. During binary fission in bacteria, first the DNA is duplicated and therefore two copies of DNA are formed. Then the bacterial cell divides into two daughter cells. Now the two daughter bacteria grow in size and divide again similarly.

b)Budding: 

         The process of budding is found in yeast, a unicellular microscopic fungus. The cells of the yeast reproduce by budding. During budding, a small outgrowth called bud' is formed on one side of the parent cell.

         The nucleus divides by mitosis into two nuclei and one of the daughter nucleus along with cytoplasm enter into the bud. Bud enlarges and finally separates as an independent cell. The bud then develops into a new organism. In some cases, the buds do not separate and colonies are formed.

c)Spore formation:

          Spore formation occurs in fungi such as rhizopus, mucor and mushrooms. Rhizopus is common bread mold. A round structure or thick walled spore sac, sporangium appears at the tips of erect hypha. The sporangium contains small asexual spores. These spores are produced by the division of a cell many times.

          The sporangium bursts on maturity and release spores. Each spore is covered with a thick wall called cyst, therefore can survive unfavorable conditions. They are light and dry, thus easily carried by wind from one place to another. When these spores reach a suitable place, they germinate and develop into a new rhizopus.

AIDS

Aids:

    It is a sexually transmitted disease (STD) that transmits through sexual act. AIDS stands for acquired immuno deficiency virus (HV). The various which cause AIDs cannot live outside the human body.

Cause:

     It is caused by human immune deficiency virus or HIV.

Mode of transmission:

    AIDS is transmitted by:

1. Transfusion of infected blood.

2. Use of infected needles and syringes.

3. Sharing razors with infected persons.

4.Immoral sexual activity.

5.Infected mother milk.

Mode of action:

      The HIV destroys white blood cells. This results in loss of resistance against infections. It is a fatal disease.

● A person infected with AIDS develops symptoms after about 10 years.

● A patient with AIDS can be infected easily with other diseases like pneumonia, cancer and other several others.

Symptoms:

     The initial symptoms of AIDS are similar to the flu including fever, swollen, lymph glands, headache and fatigue. The virus may remain dormant in the body for years and many people have no symptoms. But the immune system of the body is destroyed gradually.

Treatment:

    There is no cure of AIDS or HIV. Antiviral drugs are used to reduce the growth and kill the HIV cells. However in many cases, these medicines do not work properly.

Warning:

    According to the latest national survey, there are approximately 97,400 cases of AlDS in Pakistan. The national AIDS control program and its provincial units are working to control this epidemic. NGOs (non-government organization) also take active part to control AIDS and creating awareness in people.