sexual reproduction in invertebrates, their advantages and disadvantages


Sexual reproduction:
In this case development of new individual takes place by the fusion of the cells or female gametes. Sexual reproduction is most common type of reproduction among the plants and animals. They are of following types

(1)        Syngamy: The fusion of two gametes takes place completely and permanently. It is of following kinds:

(i) Autogamy: In this case male and female gametes are produced by same cell or organism and both gametes fuse together to form a zygote e.g. Paramecium and Actinosphaerium.
(ii) Isogamy: It is the fusion of morphologically and physiologically identical gametes and are called isogametes i.e. same gametes.
(iii) Anisogamy: Some organisms produce two types of gametes. Both types of gametes differ from each other in their shape and size and are known as an isogametes or heterogametes. Male gametes are motile and small in size and are known as micro gametes. Female gametes are passive and have large size and are known as macro or mega gametes. The union of micro and mega gametes is known as anisogamy.

(2)        Conjugation: It is temporary union of two individuals of same species. During the union both individuals known as conjugants exchange certain amount of nuclear (DNA) material and after this conjugants are separated e.g. Paramecium.

(3)        Automixis (Autogamy): When the gamete nuclei of the same cell unite together to form new individuals, this phenomenon is known as automixis of Autogamy e.g. Paramecium.

Advantages of sexual reproduction:

(1) New combination of traits can arise more rapidly in sexually reproducing animals because of genetic recombination.
(2) The resulting genetic diversity increases the changes of the species surviving sudden environmental changes.
(3) Variation is the foundation for evolution.
(4) Sexually reproducing population tend to eliminate deleterious and lethal mutations.

Disadvantages:
(1) An animal that cannot reproduce asexually can never bequeath its own set of genetic material to its progeny.
(2) Sexual reproduction bestows on the progeny a reassessment of maternal and paternal chromosomes.
(3) The same mixing processes that create the adaptive gene combinations in the adult work to dismantle it partially in the offspring.
(4) Many of the gametes that are released are not fertilized leading to a significant waste of metabolic effort.
Sexual reproduction is primary mode of reproduction in animals. It is the type of reproduction which involves sex cells, the gametes. A male gamete, the sperm fuses with female gametes, the ovum, to form a zygote which undergoes development and new individual is formed. This type of reproduction involves two parents, a male who contributes the sperm and a female who contributes the ovum. Taenia solium (Tapeworm) is hermaphrodite i.e. having both male and female reproductive organs present in the same animal. Earthworm is also hermaphrodite. They are also called monoecious i.e. having both sexes. In some invertebrates these is self fertilization and others there is cross fertilization due to maturation of sperms and eggs at different times.

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