Protective Membranes Of The Ovum
The egg in humans contains two major protective layers the corona radiata containing follicular cells, and the zona pellucida. The corona radiate can be made of 2 or 3 layers of cells while the zona pellucida is a clear thick membrane made of glycoproteins. The corona radiata needs to be enzymatically overcome by sperm before reaching the zona pellucida. Binding of the sperm to this inner glycoprotein membrane induces the release of hydrolytic enzymes from the acrosome. This mediates the fusion of the sperm membrane with the plasma membrane of the egg, facilitating the fertilization of the two haploid nuclei. The release of digestive enzymes and the subsequent steps are called the acrosomal reaction and it elicits a response from the egg membranes as well. The ovum forms a vitelline membrane that prevents the further entry of any other sperm. Egg membranes are also believed to play a role in maintaining species specificity during fertilization, preventing the egg membranes from being accessed by sperm of a different species.
What Is Sexual Reproduction Biology Class 10
-It is a process that involves the fusion of gametes from two sexes that is male gamete and female gamete. That results in the formation of a zygote which eventually grows to become an individual similar to its parents. -Sexual reproduction is most commonly seen in humans, most animals, and some plants.
What Is A Diploid In Biology
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Haploid cells have one complete set of chromosomes, whereas the term monoploid refers to the number of unique chromosomes in a biological cell. In diploid organisms, diploid cells contain the complete set of necessary chromosomes, while haploid have only half the number of chromosomes found in the nucleus.
Also, what is gametes in biology? Gametes are the cells used during sexual reproduction to produce a new individual organism or zygote. The male gamete, sperm, is a smaller, mobile cell that meets up with the much larger and less mobile female gamete, egg or ova. Both sperm and egg are only haploid cells. They only carry half of the chromosomes needed.
Beside above, what is a haploid in biology?
Haploid is the term used when a cell has half the usual number of chromosomes. A normal eukaryotic gamete organism is composed of diploid cells, one set of chromosomes from each parent. However, after meiosis, the number of chromosomes in gametes is halved.
What is difference between haploid and diploid?
Difference Between Haploid And Diploid. The most obvious difference between Haploid and Diploid is the number of chromosome sets that are found in the nucleus. Haploid cells are those that have only a single set of chromosomes while diploid cells have two sets of chromosomes.
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Realtime Imaging Of Female Gamete Formation In Plants
New research from Japanese scientists offers a glimpse of how female gametes’ cell fates are determined and shows promise for future progress in plant breeding
Institute of Transformative Bio-Molecules , Nagoya University
image: Development of the female gamete was observed over 20 hours, clearly showing the division of the nuclei and formation of the egg, central and synergid cells.view more
Scientists from Nagoya University, Yokohama City University and Chubu University have developed a system which enables the live imaging of the formation of the female gamete in plants.
In flowering plants, the sperm cell and egg cell meet and fertilization takes place in the flower. While sperm cells are made in the pollen, egg cells are made in the ovule, the structure that becomes the seed. However, as the ovule is buried deep within the pistil, it has thus far been impossible to observe the formation of the egg cell in living plants.
The time at which cell fate is determined is significant because it gives us an insight into how plants remain adaptable to environmental conditions by flexibly changing cell fate and thus ensuring the survival of crucial cells such as gametes.
What Is A Gamete
A gamete is a reproductive cell produced as a result of sexual reproduction of both animals and plants. The main feature of gametes is the presence of half of the chromosomes when compared to a vegetative cell of the same species. Therefore, meiosis is the susceptive form of cell division involved in the production of gametes. Generally, most organisms are heterogamous and they produce two types of gametes as male and female gametes. Moreover, heterogamy or anisogamy refers to the union of gametes of two different sizes and shapes while isogamy refers to the union of gametes of opposite sexes with similar size and shape.
Figure 1: Formation of Gametes
Furthermore, gametes are produced inside sex organs. Male gametes are produced inside antheridia while female gametes are produced inside archegonia in plants. On the other hand, in animals, they are produced inside testis and ovaries, respectively. However, the main function of gametes is to fuse with the opposite gamete to form the zygote.
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Structure And Function Of Sperm
Human sperms are highly specialized cells that have undergone an extensive period of differentiation.
As shown in the image, sperms contain four morphological regions the head, neck, midpiece, and tail. These generic terms are in fact referring to different subcellular organelles that have been adapted to aid the sperm in its function.
The head, for instance, contains the genetic material. The DNA in a mature sperm is highly compacted, has nearly non-existent transcriptional activity and all the chromosomes are tightly condensed. They even have special proteins called protamines to pack the DNA more tightly than histones. The head is also surrounded by a cap-like structure containing hydrolytic enzymes called the acrosome. Acrosomal enzymes act on the outer membranes of the egg, allowing the DNA in the sperm access to the plasma membrane of the ovum.
The neck of the sperm is made of a pair of centrioles. The proximal centriole enters the oocyte during fertilization and even duplicates within the zygote. The distal centriole gives rise to filamentous structures that form the lashing tail of the sperm.
What Is Reproduction Explain
1 : the act or process of reproducing specifically : the process by which plants and animals give rise to offspring and which fundamentally consists of the segregation of a portion of the parental body by a sexual or an asexual process and its subsequent growth and differentiation into a new individual.
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Types Of Sexual Reproduction
The type of sexual reproduction of an organism is largely dependent on the size and shape of its gametes. Some male and female gametes are of similar size and shape, while others are vastly different. In some species of algae and fungi, for example, male and female sex cells are almost identical and both are usually motile. The union of similar gametes is known as isogamy.
The process of gametes of dissimilar size and shape joining is called anisogamy or heterogamy. Higher plants, animals, and some species of algae and fungi exhibit a special type of anisogamy called oogamy. In oogamy, the female gamete is non-motile and much larger than the fast-moving male gamete. This is the type of reproduction that occurs in humans.
Factors Linking Microtubules And Gamete Nuclei For Migration
It has been proposed that gamete nuclei associate with microtubules through the microtubule motor proteins, dynein, and kinesin. Cytoplasmic dynein was seen to be enriched around the gamete nuclei of the one-cell embryo in C. elegans and functional disruption of dynein by RNA-mediated interference resulted in female gamete nuclei of C. elegans unable to migrate . A defect in male gamete nuclear migration in unc-83 mutant could indicate the role of kinesin for gamete nuclear migration in C. elegans. In Drosophila, there has been no report of dynein function for gamete nuclear migration. A kinesin like protein 3A mutant gene prevented female gamete nuclear migration in D. melanogaster , confirming the requirement of the microtubule motor protein for female gamete nuclear migration.
Figure 3. Factors linking cytoskeleton and gamete nuclear envelope for migration in animals and its one possible model in flowering plants . In animals, the LINC complex, containing KASH domain protein in the outer nuclear envelope and SUN in the inner nuclear envelope, links nucleus-kinesin/dynein-microtubules. In flowering plants, the LINC complex links nucleus-myosin-actin in somatic cell nuclei and the pollen tube vegetative nucleus. Like animals, the SUN domain protein is present in the inner nuclear envelope in flowering plants that is connected with the outer nuclear envelope embedded proteins, WIT1/2 and WIP.
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What Are Somatic Cells
Somatic cells are any type of a biological cell, typically the regular type of body cells other than the reproductive cells. That means, somatic cells are only involved in the asexual reproduction. Somatic cells are diploid in humans, containing two sets of homologous chromosomes. During asexual reproduction, somatic cells are produced by mitosis, creating identical two copies of new cells from a single mother cell. However, some species contain haploid somatic cells. Haploid somatic cells can be found in species, which develop alterations of generations.
Somatic cells are originated from stem cells. The stem cells in the zygote are differentiated into distinct types of somatic cells, which are capable of creating structures like organs in multicellular organisms. The differentiation of stem cells into a particular somatic cell type in the body depends on the time of differentiation and environmental factors. Functions of the differentiated somatic cells can be completely different from each other. An adult human body may contain around three trillion of somatic cells in the body. They are differentiated into form neuron cells, blood cells, muscle cells, liver cells, etc. Neurons come together to form the nervous system. Blood cells are a part of the cardiovascular system. Cells like liver cells and stomach cells are involved in the formation of the digestive system. Red blood cells in the cardiovascular system are shown in figure 1.
Figure 1: Red blood cells
Ova Development In Oviparous Animals
In the oviparous animals the ova develop protective layers and pass through the oviduct to the outside of the body. They are fertilized by male sperm either inside the female body , or outside . After fertilization, an embryo develops, nourished by nutrients contained in the egg. It then hatches from the egg, outside the mother’s body. See egg for a discussion of eggs of oviparous animals.
The egg cell’s cytoplasm and mitochondria are the sole means the egg can reproduce by mitosis and eventually form a blastocyst after fertilization.
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Sex Determination In Birds
In birds , the female produces two different types of eggs, since they are the heterogametic sex. This means that a diploid somatic cell in adult female birds has two different types of sex chromosomes. These two chromosomes are called the Z and W chromosomes to distinguish them from the XY sex-determination system. Males have two Z chromosomes and therefore produce sperm, all of which contain only a Z chromosome. In essence, it is the genetic composition of the egg that determines the sex of the offspring, in direct contrast with the genetics of humans and many other animals.
Gamete Or Zygote Intrafallopian Transfer
Gamete intrafallopian transfer is used for infertile women who are ovulating but have blocked oviducts or for infertile couples who, for religious reasons, wish to avoid fertilization outside the human body. Mature ova are removed from large follicles in the infertile woman’s ovary, as in the IVF method. Then the ova are inserted by laparoscopy into one of the woman’s oviducts below the point of blockage and the husband’s sperm is also placed into the oviduct with the ova. Fertilization and implantation then can occur steroid hormones may be administered to assist implantation and prevent miscarriage.
In a variation of this method, ova are removed and fertilized with the husband’s sperm in vitro. Then, zygotes are inserted into the oviduct and allowed to travel down the oviduct before implantation. This is called zygote intrafallopian transfer . Success rates for ZIFT and GIFT are about the same as for IVF. These techniques are not widely used and account for a very small fraction of the ART cycles performed in the United States.
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What Are 2 Types Of Asexual Reproduction
Asexual reproduction
- Binary fission: Single parent cell doubles its DNA, then divides into two cells.
- Budding: Small growth on surface of parent breaks off, resulting in the formation of two individuals.
- Fragmentation: Organisms break into two or more fragments that develop into a new individual.
The Unique Fertilization Processes Of Red Algae
Unlike those of brown algae and animals, red algal male gametes are immotile and their movement relies on aquatic currents and diffusion. The female gamete develops a trichogyne, a hair-like cytoplasmic extension, that adheres to the male gamete . After adhesion, the spermatial nucleus undergoes mitosis and generates two nuclei . Both nuclei enter the female gamete trichogyne one moves toward the egg nucleus and the other moves to the opposite direction and stops at the tip of the trichogyne .
Figure 5. Fertilization in Red algae. Female gamete adheres to the male gamete through trichogyne . After adhesion, spermatial nucleus undergoes mitosis and generates two nuclei one migrates toward the female nucleus through trichogyne using F-actin and the other moves toward the tip of the trichogyne .
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Microtubules Play A Pivotal Role In Animal Gamete Nuclear Migration
Detailed observation of gamete nuclear migration was first performed in the sea urchin, Lytechinus variegatus. Using light microscopy, Chambers discovered that sperm asters were generated around the sperm nucleus during migration . Longo and Anderson utilized electron microscopy in the sea urchin, Arbacia punctulata, and visualized essential ultrastructural components of the sperm aster including the centrioles. Two centrioles and pericentriolar materials around them constitute the centrosome that serves as the microtubule organizing center, generating radially arrayed microtubules around the sperm nucleus.
Figure 2. Migration and fusion of egg and sperm nuclei in the sea urchin egg cytoplasm. The sperm aster forms around the base of the sperm head after incorporation into the egg cell. Astral microtubule interacts with the female gamete nucleus . Astral microtubules increase in length, pushing the male gamete nucleus and pulling the female gamete nucleus for fusion . The complex then moves to the center of the egg to complete the fertilization process .
Development Of Male Gametophyte
Pollen grains display germination that is initiated in pollen sac which is referred to as precocious germination wherein a large central vacuole formation causes the nucleus to be pushed to one side post which the nucleus goes through mitosis that gives rise to two daughter nuclei.
The small cell that is formed is known as the generative cell and the larger cell is known as the vegetative cell which has cytoplasm in sufficient amounts acting as a food reserve for the male gametophyte to develop, while the generative cell assembles at the mid-section of the pollen grain. At this phase, the pollen grains fall on the stigma wherein further development takes place.
The falling of the pollen grains on the stigma causes the nutrient absorption through the germ pore from the stigma which causes the vegetative cell to enlarge. The enlargement causes the intine to move out via the germ pore for the formation of the pollen tube.
The nuclei of the vegetative and generative cell travel to the pollen tube. The generative cell at this stage divides to produce two haploids, the non-motile and unicellular male gametes. For the deeper insertion of the tube, the size of the developed male gametophyte is diminished and derives the nutrition from the styles tissues.
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Determination In Insects And Other Invertebrates
Different insects have different patterns of sex determination. In butterflies and moths , females are heterogametic and males are homogametic. W and Z chromosomes determine the sex in Lepidoptera. Female characteristics are associated with the W chromosome. The absence of the W chromosome results in the development of ZZ chromosomal males whereas ZO chromosomal content results in the development of females.
A moth, Talaeporia tubulosa, determines the sex, in absence of the W chromosome, by using the ambient temperature. Warm temperatures result in the formation of more female eggs and colder conditions result in a greater number of males. This is a good example of adaptation wherein certain conditions, e.g., warmth, tend to favor the formation of more female progeny as warm conditions will ensure the availability of resources for the subsequent reproduction.
In grasshoppers, XX/XO sex-determination system, which is a single-chromosome system, is used. The males possess only one sex chromosome i.e., XO whereas females are XX and homogametic.
Similarities Between Gamete And Gametophyte
- Gamete and gametophyte are two related structures of plants, which undergo the alteration of generations.
- They collectively form the haploid or gametophyte phase of the life cycle.
- Moreover, they are responsible for the sexual reproduction of plants.
- Their main function is to produce a zygote, which develops into a sporophyte, which represents the diploid phase of the life cycle.
- Besides, both structures can be found in the form of male and female structures.
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Artificial Gametes In Reproductive Science And Medicine
AGs represent powerful tools for elucidating the molecular physiology of gametogenesis and associated mechanisms underlying infertility . Use of AGs could also assist research programs by providing large numbers of gametes at defined time points, reducing numbers of animals required for research, ensuring a more predictable supply than is normally encountered with animal models, and eliminating the need for human donors and the complicated ethical procedures involved. Moreover, the ability to manipulate AGs in vitro to create transgenic animals would be invaluable , representing a rapid alternative to current techniques with the benefit of reduced cost and labor. The ability to generate human gametes will potentially allow the study of multigenerational human genetics in vitro. Such research may also facilitate generation of ideal universal donor cells, with appropriate combinations of haplotypes at histocompatibility loci .