CELL DIVISION

What is the difference between mitosis and meiosis?

Mitosis is the division of somatic cells, whereas meiosis is a special type of division that occurs only in gametic cells.

What is the cell cycle?

The cell cycle is the transition of a cell from one interphase through cell division and back to interphase.

What are the four major stages of the cell cycle?

The four major stages of the cell cycle are gap 1 (G1), synthesis (S), gap 2 (G2), and mitosis (M).

What is the longest stage of the cell cycle?

The longest stage of the cell cycle is G1, which typically lasts about 9 hours.

What is the purpose of dividing cells in cytogenetics?

Dividing cells are needed in order to study chromosomes using traditional cytogenetic techniques, and many cytogenetic abnormalities result from errors in cell division.

What is G0 phase?

The arrested phase in the cell cycle where a cell might be permanently arrested if it does not undergo further division.

What happens during the synthesis phase?

DNA replication occurs, and the chromosomes consist of two identical sister chromatids.

What is the difference between early and late replicating DNA?

Early replicating DNA contains a higher portion of active genes than late-replicating DNA.

What is the duration of Gap 2?

Gap 2 lasts about 3 hours.

What is the final step in the cell cycle?

Mitosis, the process by which cells reproduce themselves, creating two daughter cells.

ural unit of the kidney is the nephron. What is the functional and structural unit of the kidney?

The nephron.

What is mitosis?

The process by which cells reproduce themselves, creating two daughter cells that are genetically identical to one another and to the original parent cell.

What happens during prophase of mitosis?

Chromosomes begin to coil, become more condensed, and begin to become visible as discrete structures. Nucleoli are visible early in prophase but disappear as the stage progresses.

What is prometaphase?

Prometaphase is a short period between prophase and metaphase during which the nuclear membrane disappears and the spindle fibers begin to appear. Chromosomes attach to the spindle fibers at their kinetochores.

What happens during metaphase of mitosis?

During metaphase, the mitotic spindle is completed, the centrioles divide and move to opposite poles, and the chromosomes line up on the equatorial plate. Chromosomes reach their maximum state of contraction during this phase.

What is the traditional focus of cytogenetics?

Metaphase chromosomes.

What is the duration of the first stage of mitosis in most mammalian cells?

Only 1-2 hours.

What is metaphase?

It is the stage of mitosis where chromosomes align in the middle of the cell.

What are the components of metaphase chromosomes?

Telomere, Metacentric, Submetacentric, Acrocentric, Centromere, Chromatids, Long arm (q), Short arm (p), Satellites, and Stalks.

What happens during anaphase?

Centromeres divide longitudinally, and the chromatids separate, migrating to opposite poles.

What is telophase?

It is the final stage of mitosis where chromosomes uncoil, nucleoli reform, and the nuclear membrane is reconstructed.

What is the result of mitosis?

Two genetically identical daughter cells, each containing the complete set of genetic material present in the parent cell.

Where does meiosis take place?

Meiosis takes place only in the ovaries and testes.

What is the result of meiosis?

The formation of haploid gametes.

What is meiosis?

Meiosis is a process involving one duplication of the DNA and two cell divisions (meiosis I and meiosis II) that reduces the number of chromosomes from the diploid number (2n = 46) to the haploid number (n = 23).

What is the difference between the diploid and haploid number of chromosomes?

The diploid number (2n) represents the total number of chromosomes in a cell, while the haploid number (n) represents half of the total number of chromosomes.

What is the purpose of meiosis?

The purpose of meiosis is to produce gametes with half the number of chromosomes as the parent cell, which is essential for sexual reproduction.

What is the difference between meiosis I and meiosis II?

Meiosis I involves the separation of homologous chromosomes, while meiosis II involves the separation of sister chromatids.

What is prophase I?

Prophase I is a stage of meiosis I that is further subdivided into several substages, including leptotene, zygotene, pachytene, diplotene, and diakinesis.

What is leptotene?

Leptotene is the first substage of prophase I, where the chromosomes begin to condense but are not yet visible by light microscopy.

What is zygotene?

Zygotene is the second substage of prophase I, where homologous chromosomes pair up and form bivalents.

What is pachytene?

Pachytene is the third substage of prophase I, where crossing over occurs between homologous chromosomes.

What is diplotene?

Diplotene is the fourth substage of prophase I, where the homologous chromosomes begin to separate but remain connected by chiasmata.

What is diakinesis?

Diakinesis is the final substage of prophase I, where the nuclear envelope breaks down, and the spindle fibers attach to the chromosomes.

What is synapsis?

Synapsis is the pairing of homologous chromosomes, locus for locus, which occurs during zygotene in meiosis.

What is the synaptonemal complex?

The synaptonemal complex is a tripartite structure that can be seen with electron microscopy during zygotene in meiosis. It is necessary for the phenomenon of crossing-over that will take place later in prophase I.

What is crossing-over?

Crossing-over is the phenomenon that takes place during pachytene in meiosis, where homologous or like segments of DNA are exchanged between nonsister chromatids of the bivalents. The result is a reshuffling or recombination of genetic material.

What are bivalents?

Bivalents are structures formed during pachytene in meiosis, where paired homologous chromosomes condense and appear as thicker threads. They are sometimes referred to as tetrads because they are composed of four chromatids.

Where does synapsis of the X and Y chromosomes occur in males?

Synapsis of the X and Y chromosomes in males occurs only at the pseudoautosomal regions, which are located at the distal short arms and are the only segments of the X and Y chromosomes containing homologous loci. The nonhomologous portions of these chromosomes condense to form the sex vesicle.

What is crossing over?

The exchange of segments of DNA between nonsister chromatids of the bivalents.

What are chiasmata?

The points where homologous chromosomes are held together only at points where crossing-over took place.

What happens during Diakinesis?

Chromosomes reach their greatest contraction during this last stage of prophase.

What happens during Metaphase I?

The bivalents line up on the equatorial plate with their centromeres randomly oriented toward opposite poles.

What happens during Anaphase I?

The centromeres of each bivalent separate and migrate to opposite poles.

What happens during Telophase I?

The two haploid sets of chromosomes reach opposite poles, and the cytoplasm divides.

What happens during telophase in meiosis?

The two haploid sets of chromosomes reach opposite poles, and the cytoplasm divides, resulting in two cells containing 23 chromosomes, each comprised of two chromatids.

What is the result of meiosis II?

The net result is four cells, each of which contains 23 chromosomes, each consisting of a single chromatid.

What is the equatorial plate in metaphase II?

The 23 chromosomes line up on the equatorial plate in metaphase II.

What is the difference between mitotic cell division and meiosis II?

Meiosis II proceeds much like mitotic cell division except that each cell contains only 23 chromosomes.

What is spermatogenesis?

Spermatogenesis is the process of producing sperm in males.

What is oögenesis?

Oögenesis is the process of producing eggs in females.

What is the effect of crossing-over and random assortment of homologs in meiosis?

Owing to the effects crossing-over and random assortment of homologs, each of the new cells differs genetically from one another and from the original cell.

What is spermatogenesis?

The process of sperm cell production in the seminiferous tubules of the male testes.

What is oögenesis?

The process of egg cell production that begins in prenatal life in human females.

What is the difference in timing between spermatogenesis and oögenesis?

The steps are the same, but the timing is different.

Where does spermatogenesis take place?

In the seminiferous tubules of the male testes.

What is the chromosome count of spermatogonia?

46 chromosomes.

What is the result of each meiotic cycle of a primary spermatocyte?

The formation of four nonidentical spermatozoa.

What is the chromosome count of secondary spermatocytes?

23 chromosomes, each consisting of two chromatids.

What is the result of meiosis II in spermatogenesis?

The formation of spermatids.

What is the chromosome count of spermatids?

23 chromosomes, each consisting of a single chromatid.

What is the final product of spermatogenesis?

Spermatozoa, or mature sperm.

When does oögenesis begin in human females?

In prenatal life.

Where do ova develop in human females?

Within the follicles in the ovarian cortex.

What is the result of mitotic cell division of oögonia?

The development of ova.

At what point in fetal development do oögonia begin to develop into ova?

At about the third month of fetal development.

What is the process by which oögonia develop into primary oöcytes?

Mitotic cell division.

What is the suspended stage of meiosis I in which primary oöcytes are arrested until postpubertal reproductive life?

Dictyotene.

What is the result of cytokinesis of meiosis I in the maturation of follicles?

A secondary oöcyte containing most of the cytoplasm and a first polar body.

What happens to the secondary oöcyte after it has been ovulated?

It begins meiosis II.

What is the result of the completion of meiosis II?

A haploid ovum and a second polar body.

What is the theoretical viability of gametes produced each menstrual cycle?

Only one out of four.

What are the chromosomes of the egg and sperm produced in meiosis II surrounded by within the cytoplasm of the ovum?

A nuclear membrane within the cytoplasm of the ovum and are referred to as pronuclei.

What are pronuclei?

The nuclei formed in meiosis II that are surrounded by a nuclear membrane within the cytoplasm of the ovum and fuse to form the diploid nucleus of the zygote.

What is the mechanism of DNA chain growth?

Possible discontinuity and unusual secondary structure of newly synthesized chains.

What is the structure of DNA?

A double helix structure consisting of nucleotides containing a sugar, a phosphate group, and a nitrogenous base.

What is the function of nucleic acids as cell constituents?

They serve as genetic material and are involved in protein synthesis.

What is the RNA codeword?

A sequence of three nucleotides that specifies a particular amino acid during protein synthesis.

What is the first mitotic division?

The division of the zygote after the male and female pronuclei fuse to form the diploid nucleus.

What is the title of the article by Nirenberg?

RNA codewords and protein synthesis.

What is the full name of the author of article 6?

Har Gobind Khorana.

What is the title of the book edited by Sharma?

Trends in chromosome research.

What is the title of chapter 2 in the book Medical genetics?

Basic cell biology: structure and function of genes and chromosomes.

What is the full name of the author of article 9?

Virginia A. Zakian.

What is the title of the article by Moyzis et al.?

A highly conserved repetitive DNA sequence, (TTAGGG)n present at the telomeres of human chromosomes.

What is the name of the protein discussed in article 12?

TRF1.

What is the title of the article by Spradling et al.?

Repetitious and unique sequences in the heterogeneous nuclear and cytoplasmic messenger RNA of mammalian and insect cells.

What is the definition of cytogenetics?

The study of the structure and function of chromosomes and their role in inheritance.

What is the difference between heterochromatin and euchromatin?

Heterochromatin is tightly packed and transcriptionally inactive, while euchromatin is loosely packed and transcriptionally active.

What are SINEs and LINEs?

SINEs and LINEs are highly repeated short and long interspersed sequences in mammalian genomes.

What is the definition of centromere?

The region of a chromosome that holds the two sister chromatids together during cell division and is essential for proper segregation of chromosomes.

What is the difference between metaphase and anaphase in cell division?

In metaphase, the chromosomes align at the equator of the cell, while in anaphase, the sister chromatids separate and move towards opposite poles of the cell.

What is the difference between spermatogenesis and oögenesis?

The events of spermatogenesis and oögenesis are the same, but the timing and net results are different. Oögenesis begins prenatally and is arrested in meiosis I until the postpubertal life of a woman

What is the result of each cycle of spermatogenesis?

Each cycle of spermatogenesis results in four functional gametes.

What is the result of each cycle of oögenesis?

Each cycle of oögenesis results in a single egg.

What is the difference between the end result of spermatogenesis and oögenesis?

Each cycle of spermatogenesis results in four functional gametes, while each cycle of oögenesis results in a single egg.

What is the difference between the timing of spermatogenesis and oögenesis?

Oögenesis begins prenatally and is arrested in meiosis I until the postpubertal life of a woman

What is the difference between the number of polar bodies produced during oögenesis and the number of polar bodies produced during spermatogenesis?

During oögenesis, two polar bodies are produced, while during spermatogenesis, no polar bodies are produced.

What is the difference between the number of functional gametes produced during spermatogenesis and oögenesis?

Each cycle of spermatogenesis results in four functional gametes, while each cycle of oögenesis results in a single egg.

What is the difference between the number of meiotic divisions that occur during spermatogenesis and oögenesis?

During spermatogenesis, two meiotic divisions occur, while during oögenesis, only one meiotic division occurs.