reproduction -it is not only production of new

Question

REPRODUCTION -

• It is not only production of new ones to increases its number but a means for the survival of a population on earth.
• Main aim is "survival and continuation or race".
• If there is no reproduction, species will become extinct just after one generation.
• Reproduction is mainly of 2 types -

S .No.	Asexual	Se x ua l
1	W ithout reproduc tive organs	Reprodutive organs present
2	No formation of gametes	Formation of gametes
3	Uniparental	Uni or biparental
4	Meiosis absent	Meiosis present
5	Offsprings are genetically similar to parents	Different
6	No variation	Variation occur
7	Possibility of extinction is increased	Evolution occur

• Animal may be unisexual or diocious (male & female are separate) and bisexual or monocious (male & female in same animal).
• Unisexual are - insects, aschahelminthes & vertebrates.
• Bisexuals are hydra, earthworm & platyhelminthes.
• Fertilization may internal (inside body) e.g. sponges, platyhelminthes, aschahelminthes, arthropoda, reptiles, birds, mammals or external (outside body) e.g. coelenterata, earthworm, some pisces & amphibia.
• Fertilization may be self (in same animal), e.g. tapeworm and crossed e.g. bisexual (protandrous e.g. hydra, earthworm, progynous e.g. sponges) & all unisexual animals.
• Protandrous means testes mature first.
• Progynous means ovary mature first.