The body is made up of trillions of somatic cells with the capacity to divide into identical daughter cells facilitating organismal growth, repair, and response to the changing environment. This process is called “mitosis.” In the gametes, a different form of cell division occurs called “meiosis.” The outcome of meiosis is the creation of daughter cells, either sperm or egg cells, through reduction division which results in a haploid complement of chromosomes so that on joining with another sex cell at fertilization a new diploid chromosomal complement is restored in the fertilized egg.[1][2][3] Show
Genomic diversity and genetic variation is produced through the process of meiosis due to chromosomal recombination and independent assortment. Each daughter cell created is genetically half-identical to that of its parent cell yet distinctly different from its parent cell and other daughter cells.[4][5] The genome is encoded by the chemical sequence of DNA nucleotides within our cells. If stretched from end to end, the DNA in one cell would span about 3 meters. In order to fit into each cell, the DNA is condensed by proteins to create “chromatin,” a complex of DNA and proteins. Somatic human cells contain 23 paired chromosomes or 46 total chromosomes. 46 is considered the “diploid” number (2n), while 23 is considered the “haploid” number (1n), or half the diploid number.[6][7] Meiosis is important for creating genomic diversity in a species. It accomplishes this primarily through 2 processes: independent assortment and crossing over (recombination).
There are 2 parts to the cell cycle: interphase and mitosis/meiosis. Interphase can be further subdivided into Growth 1 (G1), Synthesis (S), and Growth 2 (G2). During the G phases, the cell grows by producing various proteins, and during the S phase, the DNA is replicated so that each chromosome contains two identical sister chromatids (c). Mitosis contains 4 phases: prophase, metaphase, anaphase, and telophase. Mitosis
The cell can now enter Interphase where it grows and replicates its DNA in preparation for division, yet again. Meiosis goes through all 5 phases of the cell cycle twice, with modified mechanisms that ultimately create haploid cells instead of diploid. In sperm cells, the male gametes, meiosis proceeds in the following manner: Meiosis I
Interkinesis/Interphase II There is a brief pause between each round of meiosis providing time for the cell to replenish proteins; however, there is no S phase. Meiosis II
In egg cells, the female gametes, meiosis follows the same general phases with only a slight variation. During telophase I, the cytoplasm divides unequally, creating a larger daughter cell and a smaller polar body. The polar body and the daughter cell both then enter meiosis II. In telophase II, the cytoplasm of the daughter cell again divides unequally and creates a daughter cell and another polar body. In addition, the polar body from meiosis I divides and forms 2 smaller polar bodies. After meiosis is completed, there is one daughter cell (1n, 1c) and 3 polar bodies (1n 1c). The polar bodies disintegrate as they do not have enough cytoplasm and proteins to survive as gametes. Clinically, errors in meiosis can create many life-threatening outcomes. The most common error of meiosis is nondisjunction, when chromatids fail to separate during either anaphase I or II, creating imbalances in the number of chromosomes in each daughter cell. Most imbalances are incompatible with life, but some will result in viable offspring with a spectrum of developmental disorders. These medical conditions include Down syndrome, Patau syndrome, Edwards syndrome, Klinefelter syndrome, Turner syndrome, Triple X syndrome, and XYY syndrome. Review Questions1. Zelkowski M, Olson MA, Wang M, Pawlowski W. Diversity and Determinants of Meiotic Recombination Landscapes. Trends Genet. 2019 May;35(5):359-370. [PubMed: 30948240] 2.Arbel-Eden A, Simchen G. Elevated Mutagenicity in Meiosis and Its Mechanism. Bioessays. 2019 Apr;41(4):e1800235. [PubMed: 30920000] 3.Vijverberg K, Ozias-Akins P, Schranz ME. Identifying and Engineering Genes for Parthenogenesis in Plants. Front Plant Sci. 2019;10:128. [PMC free article: PMC6389702] [PubMed: 30838007] 4.Gheldof A, Mackay DJG, Cheong Y, Verpoest W. Genetic diagnosis of subfertility: the impact of meiosis and maternal effects. J Med Genet. 2019 May;56(5):271-282. [PMC free article: PMC6581078] [PubMed: 30728173] 5.Simpson B, Tupper C, Al Aboud NM. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Jun 8, 2021. Genetics, DNA Packaging. [PubMed: 30480946] 6.Ishiguro KI. The cohesin complex in mammalian meiosis. Genes Cells. 2019 Jan;24(1):6-30. [PMC free article: PMC7379579] [PubMed: 30479058] 7.Crickard JB, Greene EC. Biochemical attributes of mitotic and meiotic presynaptic complexes. DNA Repair (Amst). 2018 Nov;71:148-157. [PMC free article: PMC6340751] [PubMed: 30195641]
Integumentary (skin) system
Each of the two strands in this illustration is called a -------__------------- ------ ^ |
The chromosomes move to the opposite poles during....
Crossing over is one of the most important events in meiosis because....
It produces new combinations of alleles on chromosomes
In mitosis, if a parent has 16 chromosomes, each daughter cell will have how many chromosomes?
1.) formation of four new nuclei, each with half the chromosomes present in the parental nucleus2.) alignment of tetrads at the metaphase plate3.) separation of sister chromatids4.) separation of the homologoues; no uncoupling of the centromere5.) synapsis; chromosomes moving to the middle of the cell in pairsA.) what's the most logical order that represents meiosis?B.) which step take place in both mitosis and meiosis?
If gastrulation was blocked by an environmental toxin, then....
Embryonic germ layers would not form
|. •|. •. •| •. •. •|__________ 1. 2. 3. A.) which sample of DNA might be form a nerve cell arrested in Gzero of the cell cycle? B.) which sample of DNA might represent an animal cell in G2 phase of the cell cycle?C.) which sample of DNA might represent a sperm cell?
If a cell has completed the first meiotic division and is just beginning meiosis II, what's an appropriate description of its contents?
It has half the amount of DNA as the cell that began meiosis
In comparing mitosis and meiosis, what's true?
Meiosis II resembles mitosis
Which of the following statements are true? A.) once a person reaches maturity, cell division stops except to repair woundsB.) cell division in an adult signifies cancerC.) some specific cells throughout the body retain the ability to divide and replace themselvesD.) growth continues throughout the life of an adult human
In the cells of some organisms, mitosis occurs without cytokinesis. This will result in...
Cells with more that one nucleus
Under favorable conditions, during which phase of meiosis will the chromosomes appear as packets of four chromatids?
Independent assortment refers to which of the following statements..?
Either partner of a homologous pair of chromosomes may end up at either spindle pole
In eukaryotic cells, which can occur during the stages of mitosis?
Fragmentation and the disappearance of nuclear envelope
Vinblastine is a standard chemotherapeutic drug used to treat cancer, because it interferes with the assembly of microtubules, its effectiveness must be related to....
Disruption of mitotic spindle formation
Though a microscope, you can see a cell plate beginning to develop across the middle of a cell and nuclei forming on either side of the cell plate. This cell is most likely...
A plant cell in the process of cytokinesis
In most animal cells, the sperm and egg contribute an equal_____ to the zygote.
By the end of this phase, the number of homologous chromosomes is reduced in half.
Sister chromatids of each chromosome are separated from each other.
The chromatids detach from one another and become visibly separate chromosomes during...
Which of these statements concerning the centromere is NOT true?A.) it appears to join duplicated DNA's B.) it anchors proteins to DNAC.) its position along the chromosome varies D.) it is the location site for microtubule attachment.
It anchors proteins to DNA
Which stage in reproduction and development occurs before the others?
Proteins that resemble spools on which DNA molecules are wound are called....
(Picture of chromatids splitting) If the cell whose nuclear material is shown in the above picture, continues toward completion of mitosis, what would happen next?
Formation of telophase nuclei
In which of the stages below does each chromosome consist of two DNA molecules? 1.) prophase 2.) metaphase3.) anaphase4.) telophase
What's not associated with meiosis?
What doesn't occur in mitosis?
Which of the following statements is false? A.) chromosomes don't pair during mitosis B.) genes and chromosomes are duplicated during prophaseC.) each species has a specific number of chromosomesD.) new nuclei are formed during telophase
In vertebrae animals spermatogensis and oogenesis differ in that...
Oogenesis ends at menopause, where as spermatogensis is finished at birth
This picture shows (it's a picture of two cells dividing)
Cytoplasmic division in an animal cell and a contractile ring mechanism
A student is looking through his light microscope (~450 X) at a squashed and stained onion root tip. Some, but not all, of the cells have clearly visible chromosomes strands. When a cell is in anaphase of mitosis, which of the following will he see?
A clear area in the center of the cell
The spread of a cancer from one site to others in the body is known as
Which of the following doesn't produce variation? A.) asexual reproduction B.) random alignment of chromosomes during meiosis C.) crossing overD.) genetic recombination of alleles
Which of these statement are false? A.) in humans, each of the 22 maternal autosomes has a homologous paternal chromosome.B.) in humans, the 23rd pair, the sex chromosomes, determine whether a person is female (XX) or male (XY) C.) single, haploid (n) sets of chromosomes in ovum and sperm unite during fertilization, forming a diploid (2n), single-celled zygote D.) at sexual maturity m, ovaries and testes produce diploid gametes by meiosis
What is produced is a cell divides by mitosis but does not undergo cytokinesis?
One cell with two nuclei, each identical to the nucleus of the parent cell
Humans produce skin cells by mitosis and gametes by meiosis. The nuclei of skin cells produced by mitosis will have....
Four times as much DNA as the nuclei of gametes produces by meiosis
A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. How many picograms would be found at the end of S and the end of G2?
You have the technology necessary to measure each of the following in a sample of animal cells: chlorophylls, organelle density, picograms of DNA, cell-wall components, and enzymatic activity. Which would you expect to increase significantly from M to G1?
Organelle density and enzymatic activity
Motor proteins require what to function in the movement of chromosomes toward the piles of the mitotic spindle?
The drug cytochalasin B blocks the function of actin. What aspects of the animal cell cycle would be most disrupted by cytochalasin B?
Cleavage furrow formation and cytokinesis
Once nerve cells become mature, they don't usually undergo cell division. Based on your knowledge of the cell cycle, you would predict that mature nerve cells become arrested in the______ of the cell cycle.
The kinetochore serves what function?
Kinetochores attach to microtubule a during mitosis
To prevent disastrous consequences, the eukaryotic cell cycle is controlled by
A series of cell checkpoints
The reproductive, cardiovascular, and muscular-skeletal systems develop from what embryonic germ layer?
In a human karyotype, chromosomes are arranged in 23 pairs. If we choose one of these pairs, such as pair 14, what do the two chromosomes of the pair have in common?
Length, centromere position, staining pattern, and traits coded for by their genes
Arrange the following in order. 1.) secondary oocyte2.) oogonium3.) ovum4.) primary oocyte
Arrange the stages of sperm development in Chronological order.1.) sperm2.) spermatid3.) primary spermatocyte4.) secondary spermatocyte5.) spermatogonium
A.) large frog on a lily padB.) partial tadpole, into full tadpoleC.) almost hallow egg into partial tadpoleD.) hollowing eggE.) full, almost fertilized egg.F.) two frogs doing the bed boogie
A.) development into an adult B.) organogenesisC.)gastrulationD.) cleavage E.) fertilization F.) sexual reproduction |
During which phase of meiosis will the chromosomes separate as packets of four chromatids (tetrad)?
Pos Terkait
Copyright © 2024 ketajaman Inc.
