Mitosis is used for almost all of your body’s cell division needs. It adds new cells during development and replaces old and worn-out cells throughout your life. The goal of mitosis is to produce daughter cells that are genetically identical to their mothers, with not a single chromosome more or less. Meiosis, on the other hand, is used for just one purpose in the human body: the production of gametes—sex cells, or sperm and eggs. Its goal is to make daughter cells with exactly half as many chromosomes as the starting cell. To put that another way, meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes. In humans, the haploid cells made in meiosis are sperm and eggs. When a sperm and an egg join in fertilization, the two haploid sets of chromosomes from a complete diploid set: a new genome.In many ways, meiosis is a lot like mitosis. The cell goes through similar stages and uses similar strategies to organize and separate chromosomes. In meiosis, however, the cell has a more complex task. It still needs to separate sister chromatids (the two halves of a duplicated chromosome), as in mitosis. But it must also separate homologous chromosomes, the similar but nonidentical chromosome pairs an organism receives from its two parents. These goals are accomplished in meiosis using a two-step division process. Homolog pairs separate during the first round of cell division, called meiosis I. Sister chromatids separate during a second round, called meiosis II. Since cell division occurs twice during meiosis, one starting cell can produce four gametes (eggs or sperm). In each round of division, cells go through four stages: prophase, metaphase, anaphase, and telophase.Before entering meiosis I, a cell must first go through interphase. As in mitosis, the cell grows during G_1 1 start subscript, 1, end subscript phase, copies all of its chromosomes during S phase and prepares for the division during G_2 2 start subscript, 2, end subscript phase. During prophase, I, differences from mitosis begin to appear. As in mitosis, the chromosomes begin to condense, but in meiosis I, they also pair up. Each chromosome carefully aligns with its homolog partner so that the two match up at corresponding positions along their full length. For instance, in the image below, the letters A, B, and C represent genes found at particular spots on the chromosome, with capital and lowercase letters for different forms, or alleles, of each gene. The DNA is broken at the same spot on each homologue—here, between genes B and C—and reconnected in a criss-cross pattern so that the homologs exchange part of their DNA.This process, in which homologous chromosomes trade parts, is called crossing over. It's helped along by a protein structure called the synaptonemal complex that holds the homologues together. The chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over; they're only shown side-by-side in the image above so that it's easier to see the exchange of genetic material.
<span>The Mediterranean dry-summer
climates usually experiences dry temperatures during summer because of the
subtropical high overhead. Mediterranean climate is also a mesothermal climate;
it means that it normally has a long, dry, and hot summer. It is usually
associated with dry summers, and in contrast, mild, rainy winters.</span>
Living organisms also contain a lot of hydrogen, oxygen, nitrogen, sulfur, and phosphorous. Those atoms combine together to form complex molecules of various types: proteins, carbohydrates, lipids, and nucleic acids.
Sister chromatids are made during the synthesis phase of the cell cycle. In the synthesis phase, the homologous chromosomes get replicated and sister chromatids are produced so they are produced by duplication of chromosomes.
As sister chromatids are produced by replication, therefore, they are identical copies of parent chromosomes. These sister chromatids are joined to each other at centromere. They get separated during the anaphase of mitosis and moves to the opposite pole.
Tyrosine is listed as a non-essential amino acid because it can be synthesised from the essential amino acid phenylalanine.
<u>Explanation:</u>
Amino acids are classified as essential and non essential according to whether they can be synthesized in the body itself or should be supplied by the diet. Essential amino acids cannot be synthesized in the body of the organism and thus can be obtained only from the diet. In the case of human beings, valine, phenylalanine, methionine etc are examples of essential amino acids.
Non essential amino acids can be synthesized within the body of the organism. Thus they need not be supplied by the diet. Alanine, aspartic acid etc are some of the non essential amino acids in human beings. It is given here that animals cannot synthesize tyrosine from shikimate-3p due to the lack of EPSP synthase.
But the amino acid tyrosine can be synthesized from the amino acid phenylalanine which is an essential amino acid. Thus tyrosine will be a non-essential amino acid.
Out of the choices given, the following bacterial cells that would be best able to survive an attack by an antibiotic is; A bacterial cell that has a cell membrane made of ester-linked fatty acids. The correct answer is B.
