02 Reproduction in Lower and Higher Animals - part 02 - Sexual reproduction in animals

02 Reproduction in Lower and Higher Animals - part 02 - Sexual reproduction in animals


Sexual reproduction in animals : 
  • It is the process which involves the production of offspring by the formation and fusion of gametes. It is also called amphimixis. 
  • In animals, gamete formation primarily involves meiosis.
  • The sexually reproducing animals show two main phases in their life time.
  1. juvenile phase 
  2. Reproductive maturity phase
  • The earlier juvenile phase mainly represents physical growth phase starting from birth. 
  • The animals can not reproduce sexually in this phase. 
  • The later Reproductive maturity phase is attained usually after physical growth is almost over.
  • It involves growth and activity of the sex organs. 
  • The animal can reproduce sexually in this phase. Both these periods (phases) are of variable duration in different animals. 
  • After attaining sexual maturity, the animal exhibits various events, namely -  
  1. Pre-fertilization (gametogenesis and gamete transfer)
  2. Fertilization (fusion of male and female gametes) and 
  3. Post fertilization events (formation of zygote and embryogenesis). 
  • The sexually reproducing animals show various breeding patterns. 
  • Some like the goat, sheep, and donkey are seasonal breederswhile humans and apes are continuous breeders. 
  • They can breed throughout the year.
 Human Reproduction : 
  • Humans are sexually reproducing animals. 
  • The process of reproduction involves various sequential steps such as - 
  1. gametogenesis
  2. insemination
  3. internal fertilization (i.e. fusion of male and female gametes)
  4. zygote formation and 
  5. embryogenesis, gestation and parturition. 
  • The gametes, sperms and eggs are produced by the primary sex organs, testis in male and ovary in female. 
  • Organs other than testis and ovary, are called secondary sex organs of the male and female. 
  • As male and female can be externally differentiated by certain specific features called secondary sexual characters, they are called sexual dimorphic characters. 
  • In males, presence of beard, moustache, hair on the chest, muscular body, enlarged larynx (Adam's apple) are secondary sexual characters.
  • In females these characters are the developed breast, broader pelvis and high pitched voice.

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