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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