The diagram Figure 5. As you can see in the meiosis diagram, two cell divisions occur during the overall process, producing a total of four haploid cells from one parent cell. The two cell divisions are called meiosis I and meiosis II. Meiosis I begins after DNA replicates during interphase. Both meiosis I and meiosis II occur in four phases, called prophase, metaphase, anaphase, and telophase.
You may recognize these four phases from mitosis, the division of the nucleus that takes place during routine cell division of eukaryotic cells. Requiring two individuals to produce offspring, however, is also the main drawback of this way of reproducing, because it requires extra steps — and often a certain amount of luck — to successfully reproduce with a partner.
On the other hand, sexual reproduction greatly increases the potential for genetic variation in offspring, which increases the likelihood that the resulting offspring will have genetic advantages. In fact, each offspring produced is almost guaranteed to be genetically unique, differing from both parents and from any other offspring.
Sexual reproduction increases genetic variation in a number of ways:. With all of this recombination of genes, there is a need for a new set of vocabulary. Remember, that sister chromatids are two identical pieces of DNA connected at a centromere.
Once crossing over has occured, we can no longer call them sister chromatids since they are no longer identical; we term them dyads. In addition, once crossing over has occurred, the pair of homologous chromosomes can be referred to as tetrads.
All of these mechanisms — crossing over, independent assortment, and the random union of gametes — work together to result in an amazing range of potential genetic variation. Each human couple, for example, has the potential to produce more than 64 trillion genetically unique children. No wonder we are all different! At the end of meiosis, four haploid cells have been produced, but the cells are not yet gametes. The cells need to develop before they become mature gametes capable of fertilization.
The development of haploid cells into gametes is called gametogenesis. It differs between males and females. This image in the public domain. Meiosis involves two nuclear and cell divisions without interphase in between, starting with one diploid cell and generating four haploid cells.
Each division, named meiosis I and meiosis II, has four stages: prophase, metaphase, anaphase, and telophase. These stages are similar to those of mitosis, but there are distinct and important differences. A human cell prior to meiosis will have 46 chromosomes, 22 pairs of homologous autosomes, and 1 pair of sex chromosomes.
You inherit one chromosome of each pair of homologs from your mother and the other one from your father. Sexual reproduction is the primary method of reproduction for the vast majority of multicellular organisms, including almost all animals and plants. Fertilization joins two haploid gametes into a diploid zygote, the first cell of a new organism. The zygote enters G1 of the first cell cycle, and the organism begins to grow and develop through mitosis and cell division.
The process that produces haploid gametes is called meiosis. Meiosis is a type of cell division in which the number of chromosomes is reduced by half. It occurs only in certain special cells of an organism. In mammals, Meiosis occurs only in gamete producing cells within the gonads. During meiosis, homologous paired chromosomes separate, and haploid cells form that have only one chromosome from each pair. As you can see from the meiosis diagram, two cell divisions occur during the overall process, so a total of four haploid cells are produced.
The two cell divisions are called meiosis I and meiosis II. Meiosis I begins after DNA replicates during interphase. Both meiosis I and meiosis II occur in four phases, called prophase, metaphase, anaphase, and telophase.
You may recognize these four phases from mitosis, the division of the nucleus that takes place during routine cell division of eukaryotic cells. At the end of meiosis, four haploid cells have been produced, but the cells are not yet gametes.
The cells need to develop before they become mature gametes capable of fertilization. The development of diploid cells into gametes is called gametogenesis. It differs between males and females. Spermatogenesis occurs in the wall of the seminiferous tubules , with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube. Immediately under the capsule of the tubule are diploid, undifferentiated cells.
These stem cells, called spermatogonia singular: spermatagonium , go through mitosis with one offspring going on to differentiate into a sperm cell, while the other gives rise to the next generation of sperm. Meiosis begins with a cell called a primary spermatocyte. At the end of the first meiotic division, a haploid cell is produced called a secondary spermatocyte.
This haploid cell must go through another meiotic cell division. The cell produced at the end of meiosis is called a spermatid. Gamete or the sex cell formation is the purpose of meiosis happens in the sex organs. Hence, it results in four daughter cells which contain half of the genetic material of the parental cells. In each meiosis, there are four phases; prophase, metaphase, anaphase, and telophase. Altogether there are eight phases in the meiotic cell division.
During the meiotic prophase, bivalents are formed, and the genetic composition is mixed at points known as the chiasma. Bivalent or tetrad is an association of homologous chromosomes formed during the prophase I of meiosis. Chiasma is the contact point where two homologous chromosomes form a physical connection or a crossing over.
Crossing over results genetic material mixing between homologous chromosomes. Therefore the resulting gametes will obtain new gene combinations showing the genetic variability among the offsprings. During sexual reproduction, gametes are formed by gametogenesis. In humans, two types of gametes are produced. They are female gametes eggs and male gametes sperms.
The gametes unite to form a zygote through fertilization. It is an important aspect in the context of reproduction. Gametogenesis is of two types, male gametogenesis spermatogenesis and female gametogenesis oogenesis. Spermatogenesis and oogenesis takes place in the gonads; testis and ovaries respectively. Both processes complete three stages; multiplication, growth and maturation. Gametogenesis involves meiosis where both spermatogenesis and oogenesis produce two sets of haploid n chromosomes.
Spermatogenesis is the process that produces male gametes; sperms. Egg production begins before birth, is arrested during meiosis until puberty, and then individual cells continue through at each menstrual cycle. One egg is produced from each meiotic process, with the extra chromosomes and chromatids going into polar bodies that degenerate and are reabsorbed by the body. Skip to main content.
Reproductive System. Search for:. Gametogenesis Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis. Spermatogenesis Spermatogenesis, illustrated in Figure 1, occurs in the wall of the seminiferous tubules, with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube.
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