The cell cycle, mitosis and meiosis — University of Leicester
Describe the chromosomal makeup of a cell using the terms chromosome, Mitosis produces two daughter cells that are genetically identical to each other, . Chromosomes, chromatids, what is the difference and how many. Mitosis is used to produce daughter cells that are genetically identical to the parent cells. The cell copies - or 'replicates' - its chromosomes, and then splits the . Mitosis and meiosis are two types of cell division involved in the genetic continuity of cells. Mitosis leads to the production of two daughter cells while meiosis.
NOVA has a good interactive side-by-side comparison of mitosis and meiosis on this page: How cells divide Meiosis sets the stage for Mendelian genetics. Consider the X and Y chromosomes. They pair in prophase I, and then separate in the first division. Each cell now has only one sex chromosome, like a haploid cell. One way of thinking about ploidy is the number of possible alleles for each gene a cell can have.
Right after meiosis I, the homologous chromosomes have separated into different cells.
What is the genetic relationship between the cells in mitosis
Each homolog carries one copy of the gene, and each gene could be a different allele, but these two homologs are now in two different cells. Though it looks like there are two of each chromosome in each cell, these are duplicated chromosomes; ie, it is one chromosome which has been copied, so there is only one possible allele in the cell just two copies of it.
The second meiotic division is where sister duplicated chromatids separate. It resembles mitosis of a haploid cell. At the start of the second division, each cell contains 1N chromosomes, each consisting of a pair of sister chromatids joined at the centromere.
Here is a simplified diagram illustrating the overall process and products of meiosis: Meiosis Overview from Wikipedia by Rdbickel. In prophase I, homologous chromosomes pair and separate in the first division Meiosis I.
The cell cycle, mitosis and meiosis
In Meiosis II, sister chromatids separate. And here is a video that walks through the steps of meiosis: It is very important that you recognize how and why cells become haploid after meiosis I.
To confirm for yourself that you understand meiosis, work through one or more of these interactive tutorials: Meiotic Segregation tutorial Chromosomes, chromatids, what is the difference and how many chromosomes are there at different times of the cell cycle and after mitosis and meiosis? Chromosomes by definition contain the DNA that makes up the fundamental genome of the cell. In a prokaryote, the genome is usually packaged into one circular chromosome consisting of a circular DNA molecule of a few million base pairs Mbp.
In eukaryotes, the genome is packaged into multiple linear chromosomes, each consisting of a linear DNA molecule of tens or hundreds of Mbp.
Chromosomes exist at all different phases of the cell cycle. The chromosome number, N, in eukaryotes, refers to the number of chromosomes in a haploid cell, or gamete sperm or egg cell.
Diploid cells all the cells in our body except our gametes have 2N chromosomes, because a diploid organism is created by union of 2 gametes each containing 1N chromosomes. A pair of sister chromatids is one chromosome because it has genetic information alleles inherited from only one parent.
A pair of homologous chromosomes, each consisting of a single chromatid in a daughter cell at the end of mitosis, has alleles from the father and from the mother, and counts as 2 chromosomes.
This chromosome number stays the same after chromosome replication during S phase: Then in mitosis, the sister chromatids of each chromosome separate, so each daughter cell receives one chromatid from each chromosome. The result of mitosis is two identical daughter cells, genetically identical to the original cell, all having 2N chromosomes.
So during a mitotic cell cycle, the DNA content per chromosome doubles during S phase each chromosome starts as one chromatid, then becomes a pair of identical sister chromatids during S phasebut the chromosome number stays the same.
A chromatid, then, is a single chromosomal DNA molecule. The number of chromatids changes from 2X in G1 to 4X in G2 and back to 2X, but the number of chromosomes stays the same. The chromosome number is reduced from 2N to 1N in the first meiotic division, and stays at 1N in the second meiotic division. Because homologous chromosomes separate in the first division, the daughter cells no longer have copies of each chromosome from both parents, so they have haploid genetic information, and a 1N chromosome number.
The second meiotic division, where sister chromatids separate, is like mitosis. Chromosome number stays the same when sister chromatids separate. Using the information above, compare these two simplified diagrams of mitosis and meiosis to visualize why cells are haploid after meiosis I.
Specifically, compare the chromosomes in cells at the end of mitosis vs the end of meiosis I, recognizing that the diagram of mitosis tracks just a single pair of homologous chromosomes, whereas the diagram of meiosis tracks two pairs of homologous chromosomes one long chromosome and short chromosome: Meiosis Overview from Wikipedia by Rdbickel The video below is geared toward a high school audience, but it does present a helpful way for recognizing how many chromosomes are present in a cell and thus the ploidy level of that cell.
While watching, see if you can recognize why the products of meiosis 1 are haploid cells: Answers to questions about the mitosis figure: The two daughter cells are the same as each other, and same as the parental cell Each rod represents a chromatid, and DNA replication results in two sister chromatids joined at their centromeres.
Each chromosome now consists of two sister chromatids. Metabolic changes assemble the cytoplasmic materials necessary for mitosis and cytokinesis. A nuclear division mitosis followed by a cell division cytokinesis.
The period between mitotic divisions - that is, G1, S and G2 - is known as interphase. Mitosis Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same genetic component as the parent cell. Chromosomes replicated during the S phase are divided in such a way as to ensure that each daughter cell receives a copy of every chromosome. In actively dividing animal cells, the whole process takes about one hour.
The replicated chromosomes are attached to a 'mitotic apparatus' that aligns them and then separates the sister chromatids to produce an even partitioning of the genetic material. This separation of the genetic material in a mitotic nuclear division or karyokinesis is followed by a separation of the cell cytoplasm in a cellular division or cytokinesis to produce two daughter cells. In some single-celled organisms mitosis forms the basis of asexual reproduction.
In diploid multicellular organisms sexual reproduction involves the fusion of two haploid gametes to produce a diploid zygote. Mitotic divisions of the zygote and daughter cells are then responsible for the subsequent growth and development of the organism. In the adult organism, mitosis plays a role in cell replacement, wound healing and tumour formation.
Mitosis, although a continuous process, is conventionally divided into five stages: The phases of mitosis Prophase Prophase occupies over half of mitosis.
The nuclear membrane breaks down to form a number of small vesicles and the nucleolus disintegrates. A structure known as the centrosome duplicates itself to form two daughter centrosomes that migrate to opposite ends of the cell.
The Cell Cycle, Mitosis and Meiosis — University of Leicester
The centrosomes organise the production of microtubules that form the spindle fibres that constitute the mitotic spindle. The chromosomes condense into compact structures. Each replicated chromosome can now be seen to consist of two identical chromatids or sister chromatids held together by a structure known as the centromere.
Prometaphase The chromosomes, led by their centromeres, migrate to the equatorial plane in the mid-line of the cell - at right-angles to the axis formed by the centrosomes.
This region of the mitotic spindle is known as the metaphase plate. The spindle fibres bind to a structure associated with the centromere of each chromosome called a kinetochore.
Individual spindle fibres bind to a kinetochore structure on each side of the centromere. The chromosomes continue to condense. Metaphase The chromosomes align themselves along the metaphase plate of the spindle apparatus. Anaphase The shortest stage of mitosis.