MENDELS EXPERIMENT ON HEREDITY

Mandel chose pea plant for his experiment due to its few characteristic features .

Short life cycle and high reproduction .

Self pollination due to presented of hermaphrodite .

Homozygous plants due to self pollination .It is easy to get pure line for several generation .

Visible seven pairs of contrasting characters.

The varieties can be crosspollinated bising emasculation method .

Mendel selected 22 varieties of pea out of 34 collected varieties .

He choose if pairs of contrasting characters for study these were-

EMBRYOGENY IN MONOCOTS

 After the resting period the zygote or oospore elongates and then divides by transverse division forming two cells be basal cell and terminal cell.

The basal cell remains towards the micropylar end do not divided further and produces a large swalled vesicular suspensor cells .It may functions as haustorium .

The terminal cell divides by another transverse wall forming two cells. 

The top cell after a series of divisions forms plumule and a single cotyledon .

The cotyledons is called as scutellum and it grows rapidly and pushes the terminal plumule to one side .The plumule comes to lie in a depression .

The middle cell undergoes repeated divisions and forms hypocotyl and radicle .

The middle cell also adds a few cells to the suspensor .

In some monocots e.g. in cereals ,both plumule and radicle are covered by sheaths developed from the scutellum called as coleoptile and coleorhiza respectively .

EMBRYOGENY IN DICOTS

In dicots the zygote elongates and then dividual by a transverse wall into two unequal cells i.e. basal suspensor cell and terminal embryo cell.

The suspensor cell divides transversely a few times to form a 6-10 celled suspensor .The suspensor helps in pushing the embryo in the endosperm .

The upper most cell of the suspensor towards the micropylar end forms haustorial cell while the lowermost cell of the suspensor towards the termimal  cell is called hypophysis .

The haustorical cell function as hausforium and the hypophyics gives rise to radicle and root cap.

The terminal embryo cell under goes two vertical and one transverse division to form eight cells arranged in two tiers .It is the the octant stage of pro-embryo .

The lower tier of 4-cells give rise to plumule and cotyledons while the upper their of 4-cells near the suspensor gives rise to hypocotyl .

The  octant pro-embryo divides periclinally to form outer single layer of dermatogen or protoderm from which the epidermis arises .

The inner cells divide further forming periblem internal to the dermatogen and plerome in the untre 

The ground meristem produces cortex and pith where as procombium gives rise to stele.

Initially the embryo is globular and undifferentiated .

With continuous growth the globular pro-embryo becomes heart-shaped due to the development of two premordials of  cotyledons.

Subsequent development gives rise to the dicot embryo which is horse-shoe shaped . 

SIGNIFICANCE OF DOUBLE FERTILIZATION

It is a common characteristics of angiosperm in which both the male gametes take part in fertilization .

Female gametophyte stops its growth at eight nucleate stage further growth continues after double fertilization .

It helps in the formation of seed and fruit .

Their is recombination of maternal and paternal characters .

The PEN formed during triple fusion develops into primary endosperm cell and it provide nourishment to the developing embryo and also to the germinating seed .

It is necessary for the  formation of viable seeds. 

ORNITHOPHILY

 The mode of pollination performed by birds is known as ornithophily .

Thus the flower involved for this are called as ornithophilous flowers.

Butea monosperma callistemon bombox agave .

These flowers show following characters 

The flowers are large ,showy , brightly coloured i.e. red ,orange or blue.

Flowers are scentless or odurless .

The flowers secrete abundant watery nectar made up of sugar .

The pollen grains are sticky .

The floral parts are commonly leathery .

Two common types of tropical pollinating birds are sunbeids and humming berds some other birds are- crow ,bulbul ,parrot and mynah.

ENTOMOPHILY

 It is most common type of zoophily where the pollination is carried out through the agency of insects like- moths , butterflies , wasps , bees ,etc .

The flower are called as entomophilous flowers they show following characteristics -

Flower are generally large if small they become conspicuous by their grouping .

They are showy or brightly coloured .

Where petals are not conspicuous other parts becomes show 

Example- Bract- Bougainvillea

                 Leaves- Euphorbia palcherrima

                Sepal - Mussuenda

                Stamen - Mimosa

Flowers contain nectar glands and pleasant fragnonce to attract insects.

These is no wastage of pollen grains so less number of  pollen grains are produced .

The pollen grains are spiny , heavy and surrounded by a yellow oily sticky substance called pollen kit .

The stamens are inserted .

Stigmas are often inserted , sticky ,unbranched etc .

Example - Minoso- touch me not

HYDROPHILY

The pollination which is accomplished through the agency of water is called hydrophily.

The flowers pollinated by water are known as hydrophilus flower.

Hydrophilous plant are ceratophyllum  ,valisnaria ,hydrila etc.

Hydrophilous flower shows following adaptation .

Flowers are small and inconspicuous .

Perianth and other floral oarts are unwettable.

Flowers are with out bright colours, pleasant frogrance and nectar glands .

Pollen grains are naked with coating and are light in weight .

Stigma is long sticky but unwettable .

Flowers are usually unisexual and open under water or at the surface of water . 

ANEMOPHILY

 It is the cross pollination conducted by the help of wind . The flowers pollinated by wind are called as anemophilous flower .

Anemophilous plants are coconut ,palm , connabes ,zeamays , grasses, rice , wheat , etc show following characters which favour wind pollination .

Wind pollination plants produce large number of dusty pollen .

Pollen grains are small and lite they may be transferred to long distance .

These pollen grains are dry and water resistant i.e. unwettable .

Flowers are small and inconspicuous .

The flower are colourless , orderless  and nectarless.

Non-essential parts are either absent or reduced .

Both the stigma and anthers are exserted .

Anthers are veratile i.e. free to swing in any direction .

Stigma is hairy , feathery or branched to catch the wind born pollen-grains .

Anemophily is highly wasteful as it is non-direction .

CELL DIVISION DURING GAMETE FORMATION

Gamete are always haploid and they possess only one set of chromosome .

In haploid parent gametes are produced by mitosis .

Example - Algae , Fungi , Bryophytes 

In plants belonging to group pteridophytes gymnosperm angiosperm  animal etc the parental body is diploid here gamete are produce through meitosis.

The cells undergoing meosis are called as meiocyte. 

SEXUALITY IN ORGANISM

If the two fusing gametes belong to the come present in case of thalloid organisms then such organisms are called homothallic .

When these gametes belongs to different parent then the organism is called as heterothallic .

In angiosperm if male and female sex organs occur in same flower then the plants are called as bisexual .

If flowers possess only one sex organs then the plant is called as unisexual .

When male flower and female flower are present in same plant body plants are called as monoecious .

If they are present in separate plant body then the plants are called dioecious. 

MECHANISM OF FERTILIZATION

The process of fertilization can be studied by the following steps are

1- Germination of pollen grains on stigma 

The pollen grains fall on the stigma by the process of pollination .

The stigma has the capability to recognize the pollen grains and only the right type or compatible pollen grains can germinate by absorbing nutrients from stigmatic surface .

At the time of germination the pollen grains slightly increase in size and their cytoplasm become active .

Pollen-pistil interaction helps in the pollen germination helps in the pollen germination .

2- Growth of pollen-tube 

After germination the pollen tube is formed and it always comes out through the germ pore.

Growth of the pollen tube is carried out by some enzymes present on the surface of the stigma .It grows down wards to the ovule .

The pollen tube contains a vegetative nucleus or tube nucleus and 2 male gametes.

By the time the tube reaces the ovule the vegetative nucleus degenerates .

3- Path taken by the pollen -tube

The pollen tube forms its way through the tissues of stigma style and ovary wall .

It moves through the solid part of stigma and style by secreting pectinases and hydrolytic enzyme.

 Pollen tube travel intercellularly and chemotropically along the concentration gradient of calcium boron inosital sugar complex 

 The style may be hollow or solid .Hollow style has a canal lined by special large cells where as the solid style has conducting tissue or transmitting tissue .

 In hallow style pollen tube travels along the canal lining and absorbs nourishment .From its living cells.

 In solid style the pollen tube grows through the conducting tissue by separating their cells by secreting pectinases .The food is obsorbed by  diffusion .

4- Entry of pollen tube into embryo sac

The pollen tube enters into embryo sac of the ovule in three

a- Porogamy -The entry of pollen tube through microphyle is called porogamy 

Ex- lily

b-Mesogamy - It is the entry of pollen tube through integument or meddle of ovule .

Ex- cucurbita

c- Chalazogamy - It is the entry of pollen tube through chalaza .

Ex- casurina , betavulgaris

5- Path of male gametes

The male gametes are non-motile so they are carried by pollen tube towards the female gametes .This process is called as siphonogamy .

The pollen tube is attracted by chemothropically active substances secreted from the filliform apparatus of synergid.

Usually the pollen tube containing 2 male gametes enters into embryo sac through any one of the synergids and then discharges their male gametes .This act destroys the synergid .

6- Fusion of gametes 

When the 2 mole gametes are discharged into the embryo sac the fusion of gametes takes place.

Out of these two male gametes one fuses with the haploid egg to form a 

     

FEATURES OF DOUBLE HELICAL STRUCTURE OF DNA

A normal DNA molecule contain two polynucleotide chains twisted around each other .

Each chain has two ends 5' end occupied with phosphate group and 3' end with hydroxy group .

DNA stands are anti parallel i.e. one strand 5' to 3' direction.

The long polynucleotide chain consists of several nucleotides i.e. deoxy ribo-neucleotide .Each nucleotide made up of a phosphate group a sugar and nitrogenous base .

Pentose sugar present in DNA is a deoxy ribose sugar phosphodiester bonds are formed between 5' carbon of sugar of one nucleotide and 3' carbon of sugar of the next nucleotide .

Nitrogenous base is attached to at 1' carbon of sugar . At this place purine base is attached by its 9' position and pyrimidine by its 3' position . The nitrogenous bases are attached to sugar by N-glycosidic bone. 

DOUBLE OR TRIPLE FERTILIZATION

Fertilization is defined as the fusion of dissimilar male gamete and female gametes to form zygote which eventually develops into embryo . 

The process of fertilization was first described by Strasburger in Monotropa in 1884.

But the mechanism of double fertilization was discovered by Nawaschin in 1898 during this experiment on fertilllaria and hillium plant it was supported by Guignard .

When the 2 male gametes are discharged into the embryosac the fusion of gametes takes place.

out of these two male gametes one fuses with the haploid polar nuclei or diploid secondary nucleus of the central cell to form triploid primary endosperm nucleus .As three nucleus are involved in the fusion process it is called as triple fusion.

In angiospermic two acts of fertilization occurs in the same embryosac i.e. one is generative fertilization and other vegetative fertilization .So this phenomenon is known as double fertilization .

Double fertilization is defined as the fusion of two male gametes brought by a pollen tube to two different cells of the same female gametophyte in order to produce two different structure .

One male gamete fuses with the egg to form a diploid zygote where as the other male gamete fuses with the diploid secondary nucleus of the central cell to form a triploid primary endosperm nucleus which later develops into  primary endosperm cell.

So double fertilization involves both syngamy and triple fusion five nuclei are involved in this process i.e. two in syngamy and three in triple fusion .

It is an unique and universal feature of angiosperms except in family orchidaceal , podostemauwe and trapacsal. 

DEVELOPMENT OF SEED

After double fertilization the ovule is develop into seed during the seed development following charges occur .

The diploid zygote develop into the embryo by a number of mitotic division . The embryo consist of the radicle . The plumule on whether the plant is monocotyledon or dicotyledon .

As the embryo reaches maturity its further growth is the suspended due to formation of growth inhibitors.

The triploid primary endosperm nucleus develops into the endosperm by a number of mitotic cell division. The endosperm provided nourishment  to the embryo .

Depending on the presence or absence of the endosperm .

The nucellus is generally used up by the developing embryo but in some seeds it persists in the form of a thin layer around the endosperm this residual nucleus is known as perisperm or nucellus.

 

The seed are two types

1- Endospermic seed or Albuminous seed

When the endosperm persists in the seed as food storage tissue these seed are called endospermic seed.

Example - maize, wheat, barley , rubber, rice , etc 

2- Non-endospermic seed 

When the endosperms is completely eaten up by the growing embryo such type of seed is called non-endospermic seed .

Example- pea, gram , bean ground nut

DEVELOPMENT OF ENDOSPERM OR ENDOSPERM FORMATION

Endosperm is a nutritive tissue and contain many reserve food materials for the developing embryo .

Usually endosperm formation begins before embryo development .

The primary endosperm nucleus resulted from triple fusion divides repeatedly to form the endosperm .

So in  angiosperm is a post fertilization product and it is triploid .

But in gymnosperm the endosperm is pre-fertilized product and it is haploid 

TYPE OF ENDOSPERM 

Depending upon the mode of its formation angiospermic endosperm is of three types are 

1- Nuclear Endosperm 

In this type of endosperm the nucleus of primary endosperm cell under goes repeated division with out being accompanied by wall formation  .

The free nuclei are then arranged at the periphery leaving a large vacuole at the center .

Cytokinesis may begin later and proceed from the periphery to center .

It is the most common type of endosperm and found in wheat ,maize , rice , sunflower etc.

So endosperm of coconut is very unique because it contain both type of endosperm i.e. nuclear , cellular.

2- Cellular Endosperm 

In this type of endosperm each and every division of the primary endosperm nucleus is followed by cytokinesis or wall formation .

The division of usually transverse but it may be vertical or oblique .

Example - datuna petunia ,peperomia etc

3- Helobial Endosperm

This type of endosperm is a intermediate type between cellular and nuclear types .

Here the first nuclear division of primary endosperm nucleus is follwed by transverse cytokinesis forming two unequal cells .

Subsequent division in both the cell are free- nuclear .

Helobial endosperm is seen is the members belonging to order helobiales of monocots.

Example- Asphodelus

So the endosperm becomes cellular from the every beginning . 

DIFFERENCE BETWEEN STIMULANTS AND HALLUCINOGENS

                    STIMULANTS                                      HALLUCINOGENS

1. These drugs stimulate the central                1. These drugs affects the nervous 

     nervous system.                                              system.

2. It makes a person more active                    2. It changes the consciousness , throughts 

    alert and wakeful.                                            and feelings and it cause hallucination of illusion.

3. They cause temporary excitement.             3. These act as a sedatives and analgesics.

  Example - caffeine , cocaine                           Example - LSD , bhang, charas             

STRUCTURE OF FLOWER

Flower is a highly modified condensed reproductive shoot.

It is the most conspicuous part of all angiosperms and it constitutes the most beautiful structure of nature being full of varity , shapes , colour and scent .

They are objectives of aesthetic, ornamental ,social religious  and cultural value .

A typical flower contains following parts 

Pedicel - It is a stalk or basal portion of the flower , flower having pedicel is called pedicellate flower where as flower with out pedicel are called sessile flower .

Thalamus - The upper swollen part of the pedicel is known as thalamus .It is also called as the receptacle .

Floral whorl - When the floral leaves are arranged on thalamus in a cyclic manner .They are called as floral whorl .

Atypical flower consist of floral whorl namely .

CALYX - First whorl , individual unit - sepal 

COROLLA- Second whorl , individual unit - petal

ANDROECIUM - Third whorl , individual unit - stamen

GYNOECIUM - Fourth whorl , individual unit - carpel 

POLLINATION

Pollination is defined as the transfer of mature pollen grains from the anther to the stigma of the same flower or in different flower  of the same plant or in different flower of different plant by the help of agents .

Pollen grains are immobile so that can not be reach the stigma by themselves and requires external agency like wind  , water , animal , insect , etc 

Theophrstus has written as pollination in cate pollen .

TYPE OF POLLINATION 

Pollination is of 2 types 1- self pollination 

             It is the transfer of pollen grains from the anther of a flower to the stigma of either the same or genetically similar flower 

Self pollination involves only one parent plant . It is of 2 types 

a- Autogamy - When the pollen are transferred from the anther to the stigma of the same flower is called autogamy .

It is possoble when anther and stigma are closed to each other .

b- Geitonogamy - In this type of pollination the pollen grains of one flower are transferred to the stigma of another flower are transferred to the stigma of another flower belonging to either the same plant or genetically   similar plant.

Geitonogamy is morphologically cross pollination but genetically self pollination .

2- Cross pollination 

Cross pollination is the transfer of pollen grainsfrom the anther of the one flower to the stigma of another genetically different flower .

It is also known as allogamy .

It may be two types 

a- Xenogamy -When the pollen grains of a flower is transferred to the stigma o a different flower on a different plant of the same species .

b- Hybridization - When pollen grain of a flower are transferred to stigma of a different flower of a different of the different species.

DEVELOPMENT OF FEMALE GAMETOPHYTE

 Development of female gametophyte occurs inside the female reproduction organ i.e. gynoecium and the whole process of development can be studied under 2 heading are 

1- Megasporogenesis - formation of megaspore

2- Megagametogenesis - formation of female gametophyte or embryosac 

Gynoecium also known as pistil .

Gynoecium is the central whorl of a flower and represent female reproductive organ .

The individual unit of gynoecium is carpel which is also equivelent  to megasporophyll .

The gynoecium may consist of a single carpel called monocarpellary or may have morethen one carpel called as multicarpellary .

When the carpels are fused together this condition is called syncarpous where as when these carpels are free this condition is known as apocarpous .

Each gynoecium consist of three parts namely

a- Stigma - It is a platform which receives pollen grain and present at the tip .

b- Style -  It is a elongated tube like structure that connects stigma with ovary.

c- Ovary- It is the basal swellen portion of pistil .The ovary contain ovules in side the chambers or locules of ovarian cavity .

PRE-POLLINATION DEVELOPMENT

Pollen grain or microspore is the first cell of male gametophyte and represents immature male gametophyte .

The development of male gametophyte starts inside the microsporangia .

The nucleus of  the pollen grain or microspore divides mitotically to form a vegetative nucleus or tube nucleus and a generative nucleus .

The nuclear division is followed by the cytoplasmic division forming a small generative cell and a large vegetative or tube cell .

The generative cell contains a callose layer which separates the cell from the pollen grain wall. But at later stage the callose dissolves and this naked generative cell comes to lie freely in the cytoplasm of the tube cell.

The tube cell has a vacudated cytoplasm which is rich in the starch protin and fats.

At this stage the pollen grain is 2 called and in most of the cases the pollen grain is discharged from the anther at 2-called stage.

POST-POLLINATION DEVELOPMENT

The post-pollination changes occur when the microspore or pollen grain falls on the stigma of pistil.

The pollen grains which are compatible absorbs water and nutrients from the stigmatic surface through germpore .

The tube or vegetative cell enlarges and comes out of the pollen grain through one of the germ pores to form a pollen tube .

The pollen tube is covered with intine and it secretes pectinases and hydrolytic enzymes which helps for the passage of pollen tube into the style.

The tube nucleus descends to the tip of the pollen tube the generative cell also passes into it and is soon  divided mitotically .into two non-motile and haploid male gametes.

Each male gamete is lenticular to spherical in out line having a large nucleus which is surrounded by thin cytoplasmic sheath .One male gamete is cosidered as one cell  .

Formation of male gametes may also occur prior to formation of pollentube in some cases .

This pollen grain or microspore with pollen tube carrying 2 mature male gametophyte .

Soit is 3 - celled and 3 -necleated structure .

The mature male gametophyte has 3 parts i.e. tip portion showing growth nuclear zone containing 2 male gametes and tube nucleus and vascular region at the distal end containing vacuoles and callose plugs 

POLYEMBRYONY

 The phenomenon of the occurrence of more than one embryo is a seed is called as polyembryony .

It was first discovered by Antony Von Leekwenhock in 1719 in contain orange seeds.

According to Ernst 1918 and Schnarf 1929 polyembryony is classified into  2 types 

a- True polyembryony 

b- False polyembryony

In true polyembryony the extra embryos are developed from the same embryosac .

True polyembryony may be of following types 

1- Simple polyembryony - It occurs due to the fertilization of many eggs of a single embryosac.

Example - gretum 

2- Cleavage polyembryony - It occurs due to the cleavage of zygote or pro-embryo into two or more units which later develop into independent embryos .

Example - orchids , crotoloria , nicotiara rustica nymphaca advera

3- Polyembryony by the cells of embryosac 

The embryo may also develop from structure like synergids and antipodal cells in the embryosac .

Example -allium odorum, ulmus

4- Adventive polyembryony -In this type the embryo are formed the cells of nucellus or integuments .

Example - opuntia

MICROSPOROGENESIS AND MICROSPORE OR POLLENGRAINS

The process of formation of microspore or pollengrain from microspore mother cell through meiosis is known as microsporegenis .

During this process the cells of the sporogenous tissue divide with the growth of anther and increase their number .

Ultimately they are transformed into microspore mother  cell or pollen mother cell .

The primary mother cell are diploid i.e. they have two sets of chromosomes .

The primary mother cell under goes meiosis to produce tetrads of haploid microspore or pollengrains which later separates from each other .

The entire pollengrain is unicellular haploid and globular in structure .

Each microspore contains a nucleus at the center and the cytoplasm .

The entire pollengrain is surrounded by two layered wall are

1- Exine - It is the outer layer of microspore which is thick round and made up of a complex substance sporo pollen.

2- Intin - It is the inner layer which is uniformly thin smooth and made up of cellulose and pectin .  

DNA is a genetic material

Properties Of Genetic Material -

The genetic material most contain all the information of chemical reaction happening in side the cell in a stable form .

The information should be in coded form .

It must be chemically and structurally stable .

It must be able to replicate itself and then pass its copy to the next generation .

It must be able express itself .

It must be capable of variation i.e. recombination and mutation which is essential for evolution .

Evidences For DNA  As Genetic Material .

Different scientiste have provided evidenced to prove DNA as the genetic material .These are 

a- Griffths experiment for transformation 

b- A very mac leod and MC carthy 

c- Horshey and chase expriment 

POLLEN PISTIL INTERACTION

 All the events which occur from the time of pollen deposition on the stigma until the entry of the pollen tube  in to the ovule are together called as pollen pistil interaction .

It is a dynamic process and involves pollen recognition by stigma for compatible  pollen .

The wrong type compatible pollen or the sterile pollen are rejected by the pistil and it does not allow the growth of pollen tube.

The right type or compatible pollen are encouraged by pistil for growth and development of pollen tubes .

After growth the pollen tubes moves towords the style toreach the ovary .

Then it enters in to embryusec of the ovule through micropylar end reach the synergid guided by filliform apparatus .

Pollen pistil interaction maintains the stability of the species and permits the reasonable degree of genetic variability with in reasonable degree of genetic variability with in the species  

TYPES OF OVULE

Depending upon the configuration and orientiation of the body of ovule in relation to funiculus three are 6 types of ovules . 

A- Orthotropous ovule - It is the straight ovule or erect ovule in which micropyle and funicle remain in straight line .

Example - pollygonum , piper 

B - Anatropous ovule - It is invented ovule .In this type of ovule the nucllus is parallel to the funicle and thevmicrophyle and chalaza remain in the stright line . Here the hilum and microphyle lip side by side and are very close to each other .

Example - hibiscus 

C - Hemitropous ovule - The body of the ovule is twisted only half way     so that it at right angle to the funicle 

Example - ranunculus

D - Campylotropous ovule - Here the ovule is horse-shoe shaped and become curved .The funicle is attached .

Example - capparis , brassicaceac

E- Amphitropous ovule - It is a transversely oriented ovule where the embryosac becomes horse-shose shaped . The micropyle is close to funicle .

Example - capsella , papaver , lemma 

F- Circinotropous ovule - The ovule is straight with microphyle facing upwards .The funicle is elongated and get coiled around the ovule .

STRUCTURE OF OVULE

Ovule is an integumented megasporangium which developed in to seed .

A typical angiospermic ovule is oval in shaped and it is present in side the ovary .

In ovary the ovule is attached to a parenchyma tissue called as placenta .

The ovule consist of mainly 2 parts a- ovule body 

                                                       b - stalk or funicle 

Ovules are attached to the placenta of the ovary by their slender stalk and this stalk is called as funiculus or funicle .

The point of attachment i.e. the attachment region of the body of ovule with the funiculus is known asas hilum .

In typical anatropous ovule ovule the part of funicle remains attached beyond the hilum along the body of the ovule forming a ridge called raphe .

The funiculus  also containa vascular strand for the supply of nourishment to the ovule .

T he body of the ovule consist of a mass of parenchymatous cells called nucellus . It is diploid and is equivalent to megasporangium .

The nucellus is covered by one or two multicellular covering known as integuments .

Ovules with one integument are called unifeymic where as the ovule with two integument are called bitegmic .

The integument leave a narrow pore at one end of the ovule known as microphyle .

The opposite end to microphyle  from where the integument are developed is called as chalaza .

In mature ovule the female gametophyte or embryosac is embedded in the micropylar region of nucellus .

APOMIXIS

Aapomixis is defined as a mode of asexual reproduction in which new individuals are formed without maiosis i. e  without formation gametes and syngamy .

 It is a special type of modes of reproduction .

APO -away or without , mixing - mixing .

The term APOMIXIS was first coined by Winklervin 1908 .

The plant which reproduce by apomixis is are known as apomicts .

Apomixis is more common in the families like asteraceae poaceae rosaceae and rataceae .

Apomixis consists of two main categories i. e. vegetative propagation and agamospermy .

In vegetative propagation plants propagated by a part off their body other than seed called as propagules .

Examples - bulbil ,bulbs , runnrrs , suckers etc without meiosis and syngamy .

 It is of 2 types 

1- Adventive embryony ; 

The embryo develops directly from the diploid sporophytic cell of the ovule viz nucellus and integument .

Example - citrus , opuntia , members of euphorbiauae and orchidauae .

2 - Gametophytic agamospermy ;When the  embryo develops from a cell of the unreduced female gametophyte .It may be 2 types is diploospore and apospory .

DEVELOPMENT OF FRUIT

 Along with the development of seeds fruit development also occurs by the growth of the ovary .

fruit is the defined as the fertilized ripened ovary with or without associated parts containing one or more seed .

Fruit shows two two scars at its two opposite ends . One is the scar of female style and the other is the scar of detachment of fruit from  the parent plant .

The wall of the ovary converted in to the skin of the mature fruit called pericarp .

In some cases the  pericarp is thin and dry and not differentiated into further example - pea , rean , calotropis , cotton etc .

But when the fruit is fleshy the pericarp is the thick and further divided into outer skiny epicarp middle fibrous mesocarp and inner stony endocarp .

Example - mango , coconut , orange , cucurbita etc .

Depending upon its development , fruit are of two types 

                                                                                          a- True fruit 

                                                                                          b - false fruit 

a -True fruit ;

When a fruit is develop from the ovary is called as true fruit .

Example - mango , mustard 

b - False fruit ; 

When fruit formation occurs other calyx , corolla , thalamus  , peduncle etc it is called as false fruit .

Example   apple - from thalamus

                cashewnot - peduncle

                pea - thalamus 

                jack fruit - sepal bract and seeds 

               mulberry - bract , sepals , seeds 

Some fruits develop without fertilization and they are seed less known as parthenocarpic fruit .

Example - banana , papaya , orange , grapes etc .

STRUCTURE OF EMBRYOSEC

In angiosperm female gametophyte also called embryosec is an oval multicellular haploid structure embedded in the nucellus at the micropylar end of the ovule .

The most commen type of embryosec in angiosperm is polygonum type .

A typical embryosec is 8 cell and 8 nucleated in immature stage but 7 celled and 8 nucleted in mature stage .

The nuclear arrangement of embryosae is 3+2+3 .

The three mycropylar cells are collectively called egg  apparatus containing 2 syneagid and one large egg cell.

The synergid or help cell cointain filiform apparatus showing finger like projection .

The synergid helps in the guidance of the path of pollentube where as egg cell represent the single female gamete of embryosec .

The three chalazal cell of embryosec is called an antipodal cell and they are the vegetative cells of embryosec which may be degenerated .

The central cell is the largest cell of embryosec which cointain two polar nuclei this two polar nucelei soon fuse to form a single diploidsewndary or fusion or definitive nucleus .

Besides thes the embryosec  also contain some vacules at the central part .  

MEGASPOROGENESIS

These is a processes of formation of megaspore from diploid megaspore mother cell theough meiosis is called as megasporogenesis .

As already known the young ovule is composed of homogenous mass of tissue called nucellus.

In the hypodermal region of nucellus to words the my cropylarend  one cell becomes enlarge and filled with dense cytoplasm containing a prominent nucellus . Such a cell called primary archesporial cell .

The archesporial cell divides transversely into outer primary parietal cell and inner primary sporogenous cell .

Primary parietal cell may divide one or more time but some time may remains undivided .

The sporogenous cell directly function as single diploid megaspore arranged in a linear tetrad mother cell or mega spore mother cell .

The megaspore mother cell undergoes meiosis to form four haploid megaspores arranged in a linear tetrad .

Out of these 4 megaspore in a the linear tetrad the upper three degenerate and the lower most remains functional towards chalazal end .  

BINARY FISSON

The parent body divided into two equal and similar halves and each half form a new individual .

In this fission out growth is not formed .

The division is equal in this fission .

The parent body is completly disappears .

This fission occurs only favoural condition .

In binary fission . no residue is left .

In binary fission the organisms is immortal .

Binary fission is seen in bacteria  , amoeba , euglena , paramecium  and etc  

DEVELOPMENT OF MICROSPORANGIUM

 The development of microsporangium is eusporangiate type  i. e. sporangium develops from several initial cells .

In anther , some cells in the hypodermal layer being to enlarge and contain denser cytoplasm and thus becomes prominant . These prominant hypodermal cells are known as archesporial initials .

The archesporial cells divide periclinally to form outer primary parietal cells and inner primary sporogenesis cells .

The primary parietal cells divide further by periclinal wall where as the primary sporogenous cella forms the inner sporogenous tissue .

STRUCTURE 

The transverse section of a typical young anther shows that each microsporangium consist of two parts.

1 - outer wall                 2- Inner sporogenous tissue 

The wall of microsporangia has 4 layer viz 

a - Epidermis - It  is the outer most layer which protects the anther and helps indehiscance .

b - Endothecium - It is the second layer lying inner to the epidermis .It also helps in protection and dehisance .It has larger cells .

c - Middle layer - It is 1-3 layer wall present below the middle layer .It surrounds the pollensec . The cells of tapetum are large , radially elongated and tetraploid.

d - Tapetum - Tapetum provides nourishment to the developing microspore mother cells and microspore  

LAYERING

Layering is a type of rooting cutting method in which adventitious roots are induced to develop on a seft stem while it is still attached to the plant .

It is performed during early spring or early rainy season.

In this process a soft based branch is difoliated in the middle where a small injury or cut is defoliated part is pegged down branch of the plant is called layer .

The layer is then separated and planted .

Layering is 4 type 1 - Mound  layering 

                                2 - Tip layering

                              3- Trench  layering

                              4 - Air  layering      

   

MICROPROPAGATION

Micropropagation is the process of formation of new plants from a small plants tissue culture technique .

Tissue culture technique involving the culturing of cells tissues and organ in suitable nutrient medium under aseptic condition in side suitable container .

The small segment of plant which  is taken for this culturing purpose is called explant.

Then culturing of explant result in formation of an undifferentiated mass of cells called as call us which later differentiated to form a large number of plants lets .

These newly formed plant lets are transferred to separated post to grow them in to plants .

This process of micropropagation using tissue culture technique is useful to producing various free plants disease free plant , homozygous diploid plants etc .

Examples are orchid ,carnation and other ornamental plants .

   

LAC OPERON

 It is the amount of lactose present in a bacterial cell .

It consist two condition 

I - Switch on condition 

When lactose amount is less in bacterial cell .

RNA polymerase binds to promoter to initiate expression .

Regulatory gene synthesis repressor protein . This protein comes and binds to operator region . 

Asa result confirmation of operator changes and it blocks RNA polymerase to move forward .

Transcription and translation cannot takes place so no enzyme formation in cell .

This condition is known as switch off condition .

II - Switch on condition 

When lactose quantity increase in the cell .

Some of the lactose come and bind to repressor protein .As a result protein confirmation  changes .

Due to change is confirmation operators get unblocked .

RNA polymerase moves forward and transcription and translation occur .

structure genes lac A synthesis transacetylase lac Y  permease and lac Z galactosidase .

This condition is known as switch on condition. 

DOWNS SYNDROME

Downs syndrome was discovered by an English physician named John Langdon down in 1866.

Downs syndrome is an autosomal , trisomic disease caused by the   presence of extra chromosome number 21.

The offspring has 47 chromosomes instead of 46 chromosomes .

The presence of three chromosomes of the same kind is called trisomy .

The defective chromosomes for downs syndrome is originated in two ways .

When an abnormal egg containing the chromosomes 23A+X fertilized with the normal sperm containing the chromosomes 22AA+XX .

When an abnormal sperm containing the chromosome 22A+Y resulting in the karyotype 45A + XY .

The symptoms include round face , broad forehead ,a mongolian type of eyelid fold , flattened nasal bridge permanently open mouth ,projecting lower lip protruding tongue , short neck , flat hands and stubby fingers .

The victim has little intelligence due to malformation of the brain . Hence they are called mongolian idiocy .

Heart and other organs may also have deformities gonads and genitalia are under developed.