![]() ![]() ![]() Unlike dog zygotes, human zygotes have been a huge source of contention in modern politics. Egg meets sperm, fertilization occurs, and a zygote is formed. Human zygotes are formed in the same way as dog zygotes. Below is a picture of the cycle for reference. The zygote then finds a suitable place, divides through mitosis, and gives rise to a new fern, for the process to begin again. Once an egg and sperm meet, either from the same gametophyte or from different gametophytes, a zygote is formed. The gametophyte even has special structures to produce the eggs and sperm. The small plant, called a gametophyte, produces both male and female gametes. Instead of making gamete directly, the spore gives rise to a new, much smaller plant when it lands in a suitable place. This may seem similar so far to sexual reproduction seen in animals. The sporophyte has special structures on the undersides of the fronds, or leaves, that produce spores. A fern plant in the diploid stage is known as the sporophyte. Fern Zygotesįerns, and other plants, feature an interesting life cycle known as the alternation of generations. The puppies are still not fully developed, and take several weeks to open their ears and eyes fully. In time they will create a litter of puppies, which the female will birth. Eventually, the cells will start to specialize and continue dividing. This single cell is now known as the zygote. During fertilization, the sperm combines DNA with the egg, producing one cell. Once an egg and sperm meet, fertilization occurs. The male dog’s sperm make their way to the female’s eggs as they travel from her fallopian tubes to her uterus. Once the gametes are made, the animals must mate. In both the male and female, the process of meiosis reduces the number of alleles in each cell to 1 instead of 2. Who doesn’t love a puppy? The process of creating a puppy starts by creating gametes. During this time, important genetic variation and recombination can take place, allowing fungi to remain adaptive in the face of adversity. This produces a diploid organism for a short time. Sometimes haploid cells combine through a process of karyogamy, or combining of nuclei. Many fungi are haploid the majority of the time. In fungi, the process of forming a zygote is a little different, because fungi have somewhat different lifecycles. The process is detailed in the following image. In many higher plants, the zygote forms when the pollen fertilizes an egg inside of ovules in the flower. Besides these differences in plants, a zygote is still formed when two gametes fuse. Many commercial agricultural crops are the results of polyploidy affecting the plant in some way, either making them bigger or making their fruits sterile so people cannot grow them and must buy more. The zygote that forms from accidental gametes can create a novel varieties of plants. Many plants do not undergo meiosis before reproducing by accident, and therefore are prone to accumulating many copies of a chromosomes as generations continue to reproduce. Often, plants have many copies of a gene with different alleles. In plants, the condition of more than two alleles in a zygote is not always detrimental. In most vertebrates besides fish, extra copies of alleles are usually detrimental. The well-known genetic defect Down Syndrome is caused by an extra 21st chromosome in humans. This is important in most animals, as the wrong number of chromosomes or alleles can produce negative effects. By reducing the number of alleles in each gene to 1, a zygote formed by two haploid gametes will have the proper number of alleles. In most animals, the gamete cells are converted to haploid cells before reproduction, in a process known as meiosis. It all depends on how many cells are needed in the final organism, and how developed the organism is at birth. Some rodents, on the other hand, only need two weeks or so before babies can be born. The African elephant, for instance, has a gestation time of over 20 months, or over a year and a half. Depending on the size of the organism at birth, the development time of the young can vary. The zygote then undergoes many round of mitosis to produce an entire organism. Multicellular organisms use a similar process, producing gametes that fuse during fertilization to produce a zygote. ![]() The organism can also produce gametes to reproduce sexually with other cells. In single-celled organisms, the zygote becomes a fully functioning organism, and can divide through mitosis to produce offspring. The cellular mechanisms present in the gametes also function in the zygote, but the newly fused DNA produces a different effect in the new cell. The DNA material from the two cells is combined in the resulting zygote. A zygote is the cell formed when two gametes fuse during fertilization. ![]()
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