Formation of gametophyte directly from sporophyte without meiosis is
A somatic cell in the nucellus directly forms an unreduced embryo sac and the diploid egg parthenogenetically develops into embryo i.e. formation of gametophyte from sporophyte without meiosis. It is known as Apospory and it is a type of Apomixis.
It is involved in apomixis (asexual reproduction).
Male gametophyte of angiosperms is shed as
In majority of angiosperms the pollen grains are shed from the anther at bi-celled stage (one generative cell and one vegetative cell) but in some angiosperms the generative cell divides forming 2 sperms prior to the dehiscence of anther & pollen grains are shed at 3 celled stage.
Total number of meiotic division required for forming 100 zygotes/100 grains of wheat is
100 zygotes requires 100 pollen grains and 100 embryo sacs. 100 pollen grains are formed from 25 microspore mother cells while 100 embryo sacs are formed from 100 functional megaspores which in turn are produced by 100 megaspore mother cells since three out of four megaspores degenerate in each case.
Double fertilization and triple fusion were discovered by
In angiosperms one male gamete fuses with the egg to form diploid zygote. The process is called syngamy. The other male gamete fuses with the two polar nuclei to form triploid primary endosperm nucleus. The process is called triple fusion. These two acts together known as double fertilization. The process was Ist demonstrated by Nawaschin & Guignard in Fritillaria & Lilium.
Development of an organism from female gamete/egg without involving fertilization is
Parthenogenesis can be defined es formation of embryo from an unfertilised egg or female gamete. Parthenogenetic plants are homozygous so, they have more importance in plant breeding and genetics.
Nucellar embryo is
Substitution of usual sexual reproduction by a form of reproduction which does not include meiosis and syngamy is called apomixis. In this phenomenon embryo is developed by some other tissue without fertilization eg. nucellus or integuments or unfertilized egg. Nucellus is a diploid tissue so nucellar embryo is apomictic diploid.
Generative cell was destroyed by laser but a normal pollen tube was still formed because
Each microspore divide by mitotic division making a smaller generative cell and a larger vegetative cell or tube cell. If generative cell is damaged then the normal pollen tube will be formed because pollen tube is formed by vegetative cell, not by generative cell of microspore.
Which is correct?
Spores are for med in lower plants by mitotic division and they may be diploid but gametes are always be made by meiosis & they are always haploid.
A diploid female plant and a tetraploid male plant are crossed. The ploidy of endosperm shall be
Diploid female plant will have 2 polar nuclei (each haploid) with which one male gamete form tetraploid male plant (male gamete of tetraploid plant will be diploid) fuses, making endosperm. So endosperm will be tetraploid.
Which ones produces androgenic haploids in anther cultures?
Androgenic haploids are produced by young pollen grains because rest all are the diploid tissue.
Male gametophyte of angiosperms/monocots is
Microspore is haploid, uninucleate, minute spore produced in large number as a result of meiosis in microspore mother cell inside the microsporangia. These are the first cell of gametophytic generation in angiosperms.
Female gametophyte of angiospermsis represented by
Embryo sac is 7-celled structure. There is a large central cell with two polar nuclei, egg apparatus with egg cell and 2 synergids present at micropylar end and its chalazal end, 3 antipodal cells are present.
Sperm and egg nuclei fuse due to
Sperm or male gamete fuses with egg or female gamete because of the attraction of their protoplast. Some chemicals are secreted by ovule or egg wall to attract the male gamete or sperm.
Entry of pollen tube through micropyle is
In porogamy the tip of pollen tube enters the micropyle, pushes through the nucellar tissue & finally pierces the egg-apparatus end of the embryo sac. If pollen tube enters through chalazal side it is called chalazogamy & if it enters laterally it is called mesogamy.
Cellular totipotency was demonstrated by
F.C. Steward & co-workers in 1964 raised the entire carrot plant from carrot-root culture. They established the cellular totipotency i.e. capacity of a cell to develop a new plant. However the idea of totipotency was given earlier by German botanist Gottlieb Haberlandt. He tried to grow isolated leaf cell but could not succeed.
Pollination occurs in
Pollen grains are found only in Gymnosperms and Angiosperms.
Embryo sac occurs in
Embryo sac is a female gametophyte which contains the egg apparatus.
Which of the following pair has haploid structures?
(a) Nucellus - 2n, antipodal cells - n
(b) Antipodal cells - n, egg cell - n
(c) Antipodal cells - n, megaspore mother cell - 2n
(d) Nucellus - 2n primary endosperm nucleus - 3n
Antipodal and egg cell are the product of meiotic division and rest are not.
Point out the odd one?
They are all found in ovule (Nucellus, Embryo sac & Micropyle) while pollen grain is male gametophyte.
Fusion of male gamete with the egg is called syngamy.
Double fertilization is fusion of
Meiosis is best observed in dividing
Microsporocytes or microspore mother cell after meiosis give rise to microspore. No any other cell (in given options) divide by meiosis.
A population of genetically identical individuals, obtained from asexual reproduction is
Cloning is a technique by which genetically same individuals can be produced without including any sexual reproduction eg. Dolly sheep. The term clone is derived from źėłķ, the Greek word for “twig”, refering to the process, whereby a new plant can be created from a twig.
Which of the following plant cells will show totipotency?
Xylem vessels and cork cells are dead while sieve tube cells do not possess nuclei.