Explain why fertilization and meiosis must alternate in all sexual life cycles.
- Explain why fertilization and meiosis must alternate in all sexual life cycles.
- Which of the following events happen during meiosis but not during mitosis
- List the phases of meiosis i and meiosis ii and describe the events characteristic of each phase.
- Explain why crossing over is observed in meiosis but not in mitosis
- Describe how the chromosome number changes throughout the human life cycle
Which of the following events happen during meiosis but not during mitosis
In sexual reproduction, two individuals’ genetic material is mixed to create genetically diverse offspring that are genetically distinct from their parents. In sexual life cycles, fertilization and meiosis alternate. The organism determines what occurs between these two cases. Meiosis, which involves the separation of the contents of the nucleus to separate the chromosomes among gametes, decreases the number of chromosomes by half, whereas fertilization, which involves the joining of two haploid gametes, restores the diploid state. In eukaryotic species, there are three types of life cycles: diploid-dominant, haploid-dominant, and alternation of generations.
The multicellular diploid stage is the most apparent life stage in the diploid-dominant life cycle, as it is in most mammals, including humans. Almost all animals follow a diploid-dominant life cycle, in which the organism’s gametes are the only haploid cells formed. Within the gonads, specialized diploid cells called germ cells are formed early in the embryo’s development (e.g. testes and ovaries). Mitosis is used to maintain the cell line, and meiosis is used to generate gametes. The haploid gametes lose their ability to divide once they have been created. A multicellular haploid life stage does not exist. The fusion of two gametes, normally from separate individuals, results in fertilization, which restores the diploid state.
List the phases of meiosis i and meiosis ii and describe the events characteristic of each phase.
Sexual reproduction is the union of two individuals’ (usually haploid) reproductive cells to produce a third (usually diploid) separate offspring (more on ploidy below…keep reading!). Sexual reproduction has a number of drawbacks when compared to asexual reproduction: it takes time and energy to find a mate, and only half of the population (females) can produce offspring. Since any member of an asexually reproducing population will produce offspring, an asexually reproducing population can rapidly outcompete a sexually reproducing population if all other factors are equivalent.
The two-fold cost of sex is depicted in this diagram. If each person produces the same number of offspring (two), the sexual population (a) stays the same size generation after generation, while the asexual population (b) doubles. https://commons.wikimedia.org/w/index.php?curid=1599721, CC BY-SA 3.0
Asexually reproducing humans, on the other hand, can only produce clones, which means that all of their offspring are genetically identical (except in the case of mutations). This can be a drawback if circumstances change abruptly and the individuals are no longer well-adapted to the new circumstances. Sexual reproduction, on the other hand, creates offspring with novel gene combinations, which can be advantageous in chaotic or volatile conditions.
Explain why crossing over is observed in meiosis but not in mitosis
Nonkinetichore microtubules elongate the cell, lengthening it and pulling the chromosomes to opposite poles. In metaphase, they expand to divide and shrink to bring them back together.
Bacteria cells are divided in half. In ideal circumstances, one bacterium will split into two bacteria every 20 minutes. They do have a single circular DNA chromosome. The fission of binary atoms will be completed.
Bacteria cells are divided in half. After about 20 minutes, one bacterium will split into two bacteria under ideal conditions. They do have a single circular DNA chromosome. The fission of binary atoms will be completed.
They are eukaryotic cell division control mechanisms that ensure cell division fidelity. Before moving on to the next step of the cell cycle, these checkpoints ensure that the steps in each phase have been correctly completed.
At the M Phase checkpoint, an internal signal appears. Until all of the chromosomes are properly connected to the spindle at the metaphase plate, sister chromatin separation does not begin in anaphase. This prevents daughter cells from inheriting extra or missing chromosomes.
Describe how the chromosome number changes throughout the human life cycle
Multicellular organisms that rely solely on asexual reproduction, on the other hand, are extremely rare. Why is it so normal to reproduce sexually? This is one of the most critical issues in biology, and it has sparked a lot of study since the second half of the twentieth century. One possible explanation is that the variation created by sexual reproduction among offspring is critical to their survival and reproduction. Mutation is the only cause of difference in asexual species. In sexual species, this is the ultimate cause of difference. Furthermore, when different parents combine their unique genomes and the genes are mixed into different combinations by the mechanism of meiosis, those different mutations are constantly reshuffled from one generation to the next. Meiosis is the division of the nucleus’ contents, which separates chromosomes between gametes. During meiosis, as well as when the gametes combine in fertilization, variation is added.
There is no doubt that species that use sexual reproduction to produce offspring benefit from evolutionary advantages. The conundrum is why, even under relatively stable circumstances, sexual reproduction continues despite the fact that it is more complex and produces less offspring for individual species. Variation is a result of sexual reproduction, so why is it important to have ongoing variations? The Red Queen hypothesis was first suggested in 1973 by Leigh Van Valen. 1 The idea was named after the Red Queen’s race in Lewis Carroll’s Through the Looking-Glass, in which the Red Queen claims that one must run at full speed just to stay put.