Sexual reproduction definition advantages example and types. hi guys in this article we know about sexual reproduction definition advantages example and types. As we know that sexual reproduction is responsible for transfer of variation in offspring from parents.
Daughters are genetically different from the parents as variation appear due to new combination of genes during crossing over and chance of segregation of chromosomes and chance of fusion of gametes. so sexual reproduction plays important role in evolution.
This article have explain what is sexual reproduction, definition of sexual reproduction, examples of sexual reproduction ,advantages of sexual reproduction and sexual reproduction types
Sexual reproduction definition
It is the type of reproduction in which there is formation and fusion of sex cells called gamets like sperm and ova and development of an organism from the zygote to embryo formation is known as embryogenesis.
So sexual reproduction is fusion of two male and female gametes to form diploid cell known as zygote. All organism have to reach certain stage of growth and maturity in their life before they can reproduce sexually this period of growth is known as Juvenile phase and it is also called vegetative phase in plants. reproductive age start after the end of Juvenile phase or vegetative phase.
Sexual reproduction characteristics
Characteristics of sexual reproduction consist of following
1) it generally involves to parents male and female so sexual reproduction is also known as by parental reproduction except some non chordates like Taenia, Fasciola
2) it involves formation and fusion of gametes
3) it involves meiosis during gametogenesis and mitotic division during development of zygote
4) it is also called as germinal reproduction as new organisms are produced from germinal cells of parents
5) daughters are genetically different from the parents as variation appear due to new combination of genes during crossing over so sexual reproduction plays important role in evolution
6) sexual reproduction involves slow multiplication
7) unit of sexual reproduction is haploid gametes and it is found in higher plants and animals.
Reproduction in animals
Male and female gametes in animals develop in gonads like testes in male and ovary in female.
According to breeding some animals are breeding throughout the year that is known as continuous breeding and some of animals breeding in seasonally that’s why it is known as discontinuous breeding and seasonally breeding animals.
In seasonally breeding animals the testis undergoes testicular cycle in the testes and their spermatogenic tissues become functional only in the specific breeding season so in some seasonally breeding mammals like bat, otter, llama.
These animals testis enlarge become functional and descent into the scrotum in the breeding season while become reduce and non-functional and acend into abdomen in other season.
But in human male, lion ,Bull ,horse and etc the testis lies permanently in the scrotum and spermatogenesis occurs throughout the year in human male testes descend into the respective scrotal sac during 7th month of development under the stimulation of follicular stimulating hormone (FSH) from anterior pituitary gland but in some mammals like elephant, Dolphin, seal , whale and echidna testis lies permanently in the abdomen that’s why it is known as intra-abdominal.
Male animals produce male gamets sperm by the process of spermatogenesis and female gametes produced ovum that is haploid gametes by the process of oogenesis and both the gametes fuse to form diploid cell that is known as zygote and development of zygote produce offspring by the process of embryogenesis and parturition that is sexual reproduction in animals.
In the case of animal male form haploid gametes known as sperm by the process of spermatogenesis and female form haploid gamete known as ova by the process of oogenesis. During sexual reproduction sperm and ovum combine and fuse to form diploid zygote.
●Sexual reproduction in animals
Sperm (male gamete) + Ova (female gamete) = zygote (diploid cell)
Zygote —- embryogenesis—offspring
Sexual reproduction in plants
And in the case of plant their reproductive organ is flower and reproductive organ are develop and mature in flower of plant.
male part of plant is known as androecium and female part of plant is known as gynoecium. Androecium consists of number of stamen which produce haploid male gamets Pollen Grain by the process of microsporogenesis
and gynoecium consists of number of carpels which produce haploid female gametes that is known as egg cell by the process of megasporogenesis. Transfer of male gametes that is Pollen grain in plant takes place by the process of pollination.
Transfer of pollen grain from anther of androecium to the stigma of gynaeocium is known as pollination
and there is different medium act as pollinator transfer like bird animals insects water bats wind etc. There are two pollen grains haploid gametes formed in androecium by the process of microsporogenesis and there is development of nuclei and seven cells in ovary of megasporangium of flower in which three nuclei is known as antipodal cells which lies in base of embryo sac and there are two in number that is known as polar nuclei arranged in centre of embryo sac and One egg cell and two synergid cells arranged at top of embryo sac.
There is two times fertilization found in flowering plant for the formation of primary endosperm and zygote that is known as double fertilization.
and double fertilization is compromise of two process 1)triple fusion in which one pollen grain and two polar haploid nuclei fuse and combined to form triploid primary endosperm
and second process is 2) syngamy give that is fusion of one pollen grain with one egg cell to form diploid zygote. in this fusion there is two times fusion is takes place that’s why fertilization is known as double fertilization in flowering plant.
●double fertilization in plants
¡) triple fusion
Pollen grain ( male gamete) + two polar nuclei (female gamete) = primary endosperm (3n)
¡¡ ) syngamy
Pollen grain ( male gamete) + egg cell (female gamete) = zygote (2n)
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Types of sexual reproduction
Sexual reproduction types categorised into two types according to fusing structure
a) syngamy b) conjugation
1) syngamy :- syngamy is the complete and permanent fusion of two gametes to form a diploid zygote it is a most common mode of sexual reproduction & syngamy is also known as fertilization.
syngamy involved in two types of gametes sperm and ovum and sperm is also called microgamete that is minute and microscopic and motile gametes are formed by the spermatogenesis process in reproductive organ called testes in male.
And ovum is also called microgametes is large a spherical and non motile and is formed by the process of oogenesis in reproductive organ called ovary in female. Both types of reproductive organs testis and ovaries are collectively called as gonads.
When two types of gonads are present in separate parents then these are known as unisexual or dioecious but when two types of gonads found in same organism then it is known as bisexual or monoecious or hermaphrodite.
2) conjugation :- conjugation involves temporary pairing of two parents called as conjugates to exchange their male pronuclei. it is found in ciliates protozoans like Paramecium. Two Paramecium of opposite mating types comes in contact by there ventral surface during swimming. they stick together through their oral groove and during conjugation process they are cilia trichocyst feeding aapartus, pellicles and ectoplasm degenerate at point of contact and make cytoplasmic Bridge this cytoplasmic Bridge is also known as conjugation Bridge by means to Paramecium mutually share genetic material.
Types of fertilization (syngamy)
On the basis of source of fusing gametes syngamy is of two types
1) Endogamy :- it involves the fusion of two types of gametes derived from the same parents that is known as endogamy, endogamy is also known as self fertilization. Endogamy found in uniparental organism like Taenia and Fasciola , but it is takes place in rare cases
2) Exogamy :- when two fusing gametes are derived from different parents that is known as exogamy and exogamy is also known as cross fertilization and it is found in biparental animals like cockroach frog human beings and it is more common methods of reproduction.
Types of syngamy according to structure of fusing garments
1) isogamy :- when to fusing gametes are morphologically as well as physiological similar to each others, it is present in protozoans so such gamets is called isogametes and their fusing process is known as isogamy
2) Anisogamy :- when two fusing gametes are morphologically and physiological different from each other like in frog rabbit human beings such gamets are known as heterogametes or anisogametes and their feeding process is known as anisogamy
3) hologamy :- when two organism themselves act as gametes is known as hologamy and it is found in unicellular organism like yeast cell.
Sexual reproduction advantages
There are following advantages of sexual reproduction
1) sexual reproduction plays important role in evolution as offspring are genetically different from the parents as variation appear due to new combination of genes during crossing over a chance of segregation of chromosomes and chance of fusion of gametes
2) sexual reproduction helps in itruducing new characters in new born child which are beneficial for them.
3) sexual reproduction plays major role in diversity of organism and variation
4) during the sexual reproduction genetic material is transferred in New born child as stable genetic material that’s not leads to frequent mutation
5) by the help of sexual reproduction several scientist use the modern technology for the food production and high yielding animals for the production of good seed variety of different types of crops like cotton potato tomato wheat rice and milk from crossing the two good variety of cows.
Sexual reproduction process
Events involved in sexual reproduction for the maintaining the consistency of chromosome number are following
2) gamete transfer
1) gametogenesis :- it involves the formation of haploid gametes from diploid gametogonia by the meiosis in the gonads such that are spermatogenesis in testis and oogenesis in ovary in animals. Male gametes and female gametes are always haploid either it will be developed from haploid or diploid parents body. In haploid organisms gametes are formed by Mitosis for example in several organism of Monera algae and fungi plant body is haploid in such cases meiosis occurs after fertilization to make the organism haploid.
Pteridophytes gymnosperm and angiosperm and majority of animals like human beings are haploid parental body. Here meiosis occurs at the time of gametogenesis.
2) gamete transfer :- for fertilization gamets comes together for fusion. usually in most of organisms male gamete is motile and female gamete is non motile. however in many algae and fungi both gamete can be motile. water is required for the movement of male gamets in simple plant of algae bryophytes and pteridophytes.
Many male gametes not be able to reach the female gametes to compensate this loss several male gametes are produced as compared to female gametes formed. this types gamete transfer is found in frog.
in seed plants pollen grains are the carriers of male gametes for the formation of seeds pollen grains produced in anther must be transferred to stigma of carpel that process is known as pollination. Pollen grains germinate on the stigma and Pollen tubes carrying the male gamets reach the ovule and discharge the male gametes near the egg. There are different types of pollination agents like wind insects water animal bats and birds.
3) fertilazation :- it involves the fusion of haploid gametes are sperm and ovum to form diploid zygote and it undergoes further development by mitotic division to form diploid offspring.