It is the process of development of new individuals through the formation and fusion of gametes. Sexual reproduction is also called amphimixis .
Sexual reproduction involves four process - (i). Formation of
haploid cells, the gametes by gametogenesis(meiosis).
(ii). Fusion of the two gametes forming diploid zygote(fertilization).
(iii). Repeated mitotic divisions of the zygote to form embryo(embryogenesis).
(iv). Growth of embryo in to new individual (development).
Characteristics of Sexual Reproduction
1. It is usually biparental.
2. Gametes are always formed.
3. Fertilization takes place.
4. It involves both meiosis and mitosis.
5. Daughter organisms genetically differ from the parents.
6. Multiplication is not so rapid as in
asexual reproduction.
PHASES IN LIFE CYCLE
Juvenile phase:
It is prereproductive phase in the life cycle of an in dividual.
It is the period of growth between the birth of an individual upto reproductive maturity.Juvenile phase is also known as vegetative phase in plants.
Reproductive phase :
The organisms reproduce offspring during this
phase.Appearance of flowers in higher plants indicate sexual maturity.
Senescent Phase:
It begins at the end of the reproductive phase when
degeneration sets in structure and functioning of the body.
Senescence is the last phase of the life span. It ultimately leads to death.
Types of flowering plants
Monocarpic plants.- These plants flower only once in their life. After flowering they produce fruits and die. All annual (e.g. Wheat , Rice) and biennial plants (e.g.
Carrot, Radish) are monocarpic.A few perennial plants are also monocarpic. A few plants show unusual
flowering behaviour – certain bamboo species (e.g.
Bambusa tulda) flower only once in their life time usually after 50 – 100 years. Strobilanthus kunthiana
(Neelakuranji) flowers only once in 12 years.
Polycarpic Plants- These plants are perennial and flower repeatedly at intervals every year(e.g. Apple , Mango, Orange, Grape vine). Very few perennial plants have flowers throughout the year(e.g. China Rose)
Animal Breeding
On the basis of time of breeding , animals are of two types. Seasonal Breeders and Continuous Breeders.
(i) Seasonal Breeders: They reproduce at particular period of the year such as frog, lizards, most birds, deer etc.
(ii) Continuous Breeders: These animals
continue to breed throughout their sexual
maturity. Examples are honey bee queen,
rabbit, mice, cattle etc.
Differences between menstrual and oestrus cycles
Menstrual cycle Oestrus cycle
It occurs in
primates(monkeys,apes and human beings) only.
It consist of menstrual phase, proliferative phase and secretory phase.
The broken
endometrium is passed out during menstruation.
It occurs in non primates (cows, dogs,etc).
It consist of a short
period of estrus followed by anestrus period.
The broken
endometrium is reabsorbed.
