FERTILE GAMETES

FERTILE GAMETESAJAY RAJ OJHAB.V.Sc. and A.HRoll no.03 AFU 3rd Batch

GAMETESTerm introduced by Gregor Mendel(from greek word gamein to marry).Cell that fuses with another cell duringfertilization inorganismsthatsexually reproduceAnisogamy is the state where a female produces the larger type of gamete called anovum(ovule in plant) and amaleproduces the smallertadpole like type called asperm(pollen grain in plant).Isogamyis the state of gametes from both sexes being the same size and shape(in unicellular species).

GAMETESInflowering plants theflowersusemeiosis to produce a haploid generation which produce gametes through mitosis but in animals reproductive organs produces gametes through meiosis and mitosis both.Carry half thegenetic informationof an individual, oneploidyof each type, and are created throughmeiosisa normal ovum can carry only anX chromosome, whereas a sperm may carry either an X or a Y so the male sperm can play a role in determining thegender of any resultingzygote , if the zygote has two X chromosomes it may develop into a female, if it has an X and a Y chromosome, it may develop into a male.

GAMETESFor birds, the female ovum determines the sex of the offspring, through theZW sex-determination systemare not exact duplicates of either of the sets of chromosomes carried in the diploid chromosomes, and often undergo random mutations resulting in modified DNAIn honey bee only mitosis process occurs that forms diploid gamete to produce drone

Artificial gametesAlso known as In vitro derived gametes (IVD), stem cell-derived gametes (SCDGs), and In vitro generated gametes (IVG), are gametes derived fromstem cells. May be a reproductive technique for same-sex male couples, although asurrogate motherwould still be required for the gestation period.

Process of gamete formation1.Spermatogenesis

2.Oogenesis

Spermatogenesis Process of formation of sperm from spermatogonium following multiple mitosis ,meiosis and differentiation finally to get haploid spermatoza able to fertilize the haploid ovary to produce doploid zygote .Steps are as follows;1.mitosis2.meiosis3.spermiogenesis

spermatogenesis

SPERMATOGENESIS Formation of spermatozoa starts with puberty and declines elderlySynchronized development of both seminiferous tubule and spermatozoaTime required to form spermatozoa from spermatogonia is 70-75 daysNo. of spermatozoa varies with hormonal disturbances but doesnot affect the duration of cycleThe time interval between two successive maturatiom is 2-3 weeks Daily 200000 millions sperm are produced and normal ejaculation contain the same amountIt is the most rapidly dividing cell

Factors affecting spermatogenesisIncreased level of gonadotrophin and testosterone enhances the sperm formationChemical carcinogens like chemotherapeutic agents ,extreme tempreture,environmental toxins decrease the no. of germ cells leads to low number of sperms

OOGENESISOogenesis,ovogenesis, oroogenesisis the production of anovum(egg cell). It is developed from the primary oocyte by maturation(5 folds increase in size).In animal it is occurred inside female reproductive organ (inside gametophyte in plant) when approximately seven million primary oocytes have been created; however, at birth, this number has already been reduced to approximately 1-2 million.Then after atresia it becomes about 2 lakhs at last it will become 26,000 ovums after further development and becomes zero at menopause

oogenesisSteps are as follows- 1.oocytogenesisNumber of primary oocytes2.OotidogenesisMeiosis IMeiosis IIFolliculogenesis3.Maturation into ovum

OOGENESIS

Factors affecting oogenesisFSH stimulates the development of graffian follicleLeutinizing hormone enhance the ovulation

gametoGENESIS

Cell typechromosomeschromatidsProcessTime of completiongametogonium(2N)2Cgametocytogenesis(mitosis)third trimesterprimarygametocyte(2N)4Cgametidogenesis(meiosisI) Dictyatein prophase I for up to 50 yearssecondary gametocyte(N)2Cgametidogenesis(meiosisII)Halted in metaphase II until fertilizationgametid(N)1Cgametidogenesis(meiosisII)Minutes after fertilizationgamete(N)1C

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