ASEXUAL REPRODUCTION IN ANIMALS

ASEXUAL REPRODUCTION IN ANIMALS

 Asexual reproduction in Animals:

    Early are several types of asexual reproduction in animals.

The most common are:

1. Binary fission

2. Multiple fission

3. Budding

4. Fragmentation

5. Parthenogenesis

      Most animals reproduce by sexual methods, but only a few animals reproduce asexually. Asexual reproduction is common among lower animals, but in some cases higher animals also reproduce by asexual means.

1. Binary fission:

      Binary means two and fission means splitting. It is common in unicellular organism like amoeba and paramecium. In this process an organism divides into two identical daughter cells.

      During binary fission, first the nucleus splits into two daughter nuclei. In second stage, the rest of the body divides forming two daughter amoebae.

2.Multiple fission:

      This is a process of repeated divisions of the unicellular organism into many small cells. It occurs during unfavorable conditions. Multiple fissions occur in unicellular organisms like many algae and some protozoans like plasmodium, a malara parasite.

      During multiple fission the unicellular organism develops protective covering called 'cyst. The nucleus divides repeatedly produced many nuclei. Many daughter cells are produced within the cyst. When the conditions are no favourable. When the conditions become favourable the cyst breaks and a large number of daughter cells are produced.

3. Budding:

       During budding, an outgrowth known 'bud' arises from the parent body. It grows in size and then may detach from the parent body forming a new organism. Budding is found in Hydra.

4. Fragmentation:

        In fragmentation, the organism breaks up into 8 or 9 pieces. Each piece develops into full size and then breaking into pieces occurs. Fragmentation occurs in a planarian. Earthworms regularly reproduce by division into two pieces.

5. Parthenogenesis:

        This type of asexual reproduction occurs in some fishes, frogs and insects. In this process, an unfertilized egg develops into a new complete organism. Queen honeybee lays eggs in the honeycomb. Many eggs remain unfertilized and develop into haploid male called drones by parthenogenesis. At the sametime, some eggs are fertilized by male bees and these develop into workers or female new queen.

Sexual reproduction in animals:

     The fusion of male and female gametes to form a zygote and the production of genetically dissimilar offspring is called sexual reproduction. Zygote is the first cell of the new offspring. It divides mitotically and develops into an embryo. Embryo grows and changes into new individual.

External and Internal fertilization

 Fertilization:

    The fusion of male gamete (sperm) with a female gamete (egg) to form a zygote is known as fertilization. Fertilization may be external or internal.

External fertilization:

     The fusion of male and female gametes outside the body of female individual is called external fertilization.

Examples:

    External fertilization is found in aquatic animals like fish and amphibians. Eggs and sperms are shed into water at the same time or with a small interval. The sperm swim and fertilize the egg. The young one also develops outside the mother body.

Internal fertilization:

     The fusion of male and female gametes inside the body of female individual is known as internal fertilization. This type of of fertihzation Occurs in land animals. In this case, more sperms and few eggs are produced, because there a little chance of wastage. perms are released by the male into the reproductive tract of female. Sperms fuse with the egg, forming a zygote. Keptile and birds lay the eggs while in mammals zygote develops into embryo inside the body and then grow to young ones.

Examples:

     Reptiles, birds and mammals.

Advantages of internal fertilization in animals

Advantages of internal fertilization in animals:

      Internal fertilization provides better chances of fertilization and survival of the embryo. For example, reptiles and birds secrete the eggs which are covered by a protective shell.

     But in mammals the embryo develops inside the mother. This increases the chances of survival. The mother provides everything that the embryo needs. The mammalian mother takes care for their young for several years.

Reproduction in rabbits:

      Rabbits are small mammals. They are used in research work.

Male reproductive system of rabbit

Male reproductive system of rabbit:

     A pair of testes in male rabbit lies outside the abdominal cavity. They lies in the serotal sacs, one on each side of the penis. Each testis consists of coiled tubes called seminiferous tubules.

    When sperms are formed in these tubules. When sperms become mature, they are stored in collecting ducts of testes and then pass to epididymis. The sperms then pass into another duct called vas deferens. These ducts join the urethra, which lies below the urinary bladder.

     The urethra transports both sperm and urine. Semen is a fluid which consists of 10% sperm and 90% fluid. When the sperms pass in the ducts from testes to urethra, prostrate glands secrete their secretions for swimming the sperms.

    Seminal vesicles produce secretions that provide nutrients to sperms. Secretion of prostate gland neutralizes the acidity of the fluid. Secretions of the copper's gland lubricate the ducts Secretion of the glands makes the semen and facilities the process of reproduction

Female reproductive system of rabbit

Female reproductive system of rabbit:

     Female reproductive system consists of a pair of ovaries and ducts. Ovaries are small, oval organs laying near the kidney in female rabbit. The outer region of ovary produces egg cells. Follicle cells surrounds and nourishes each egg cell. Ovaries release egg cells in fallopian tubes.

    The wide fallopian funnel lies close to the ovary. Fertilization occurs in fallopian tube and the fertilized egg or zygote is carried to uterus. The two utri combine and open into vagina or birth canal which unites with urinary bladder Urinogenital canal is common and opens to the outside at vulva or genital aperture. No prostrate glands exist in female.

 Fertilization and development occurs in rabbit

       Male rabbit deposits its sperm in the vegina (birth canal) of female. Sperms swim, reaching to fallopian tubes where they fertilize the egg cells, released from ovary. After fertilization, Zygote is carried to uterus. Zygote grows forming an embryo. The embryo is connected in uterus, called placenta. Embryo develops into new offspring (rabbit kit) in 30-32 days, after which it is born.

Types of reproduction in animals, Asexual reproduction in plants, What is asexual reproduction, Asexual reproduction examples