Mitosis and meiosis Flashcards
Define mitosis
Creation of 2 daughter nuclei identical to each other and to the parent nucleus in chromosome number and genetic composition
Continuous process of change
Conservative
Define meiosis
Yields 4 haploid daughter nuclei, each with half as many chromosomes as parent nucleus
All differ in genetic composition
Part of sexual life cycle
Balanced by fertilization in which 2 sex cells combine and restore the full chromosome number
Reproduction and growth in the multicellular organism requires…
The multiplication of cells
Successful multiplication requires…
That the genetic information contained in the parent cell be transferred to the daughter cells
As all genetic materials are contained within the nucleus, this process requires nuclear division
Describe interphase in mitosis
Period between successive nuclear divisions during which chromosomes are diffuse, nucleolus is present, and nuclear envelope is intact
DNA/protein complex forms chromatin
First two important things in interphase:
1) Genetic material (DNA) is replicating to provide full complement of genetic information to each daughter cell
2) Cell is building up a sufficiently large store of energy to carry through the process of division
Last two important things in interphase in mitosis:
3) New organelles are formed in order that daughter cells contain the necessary complement of organelles
4) Centrioles (in animal cells, and some protists, not plant cells) replicate so that two pairs are formed, one destined for each daughter cell
Describe prophase in mitosis
The first stage of nuclear division
Chromosomes condense from diffuse, threadlike material to discrete, compact bodies
First two important things happening during prophase in mitosis:
1) Nucleolar material disperses
2) Pairs of centrioles move away from each other to opposite ends of cell
Last two important things happening in prophase in mitosis:
3) Other microtubules running between pairs of centrioles make up the spindle (2 ends of spindle = poles, middle region = equator)
4) Individual chromatin fibers supercoiling until they are seen as distinct chromosomes
Factors of the distinct chromosomes in prophase in mitosis:
Each chromosome consists of 2 elongated structures, chromatids, associated with each other at centromere region
Each chromatid consists of a single molecule of DNA and associated proteins (histones)
Paired chromatids are…
Identical copies of each other called sister chromatids
Why is condensation of chromosomes extremely important in prophase in mitosis?
Without it, movement could not occur without entanglement
Describe metaphase in mitosis:
Centromeres of highly supercoiled chromosomes are lying on the equator
First two important things happening during metaphase in mitosis:
1) Chromosomes migrate to central plane of cell and arrange themselves along equator
2) Chromosomes attach to spindle fibers at the centromeres
Last important thing during metaphase in mitosis:
3) Chromatids move slightly apart from centromere region, sister chromatids now oriented toward opposite poles
Describe anaphase in mitosis:
Sister chromatids separate and move to poles, drawn by shortening spindle fibers
Lasts from when chromatids separate to when moving chromosomes converge at poles
First three important things in telophase in mitosis (last phase):
1) Spindle breaks down
2) Nuclear envelope reforms around each group of chromosomes
3) Chromosomes unwind and become diffuse
Last two important things in telophase in mitosis:
4) Nucleoli reappear in daughter nuclei
5) Cell divides in 2 by means of constriction of plasma membrane (in plants, it’s new formation of cell wall/plate which grows in the middle of the cell)
What happens after telophase in mitosis?
Chromosomes regain threadlike appearance and return to interphase
What is cytokinesis?
Division of cytoplasm and cell itself
Mitosis is followed by…
Cytokinesis
How is cytokinesis usually accomplished?
Furrowing or constriction of membrane
How is cytokinesis accomplished in a plant cell due to the presence of a cell wall?
1) As mitotic spindle breaks down, membranous vesicles appear in region of equatorial plate and begin to lay down a cell plate, the beginning a new cell wall
After cytokinesis, daughter cells contain…
Their necessary components
Mitosis guarantees…
The precise distribution of chromosomes
No system exists to assure equal distribution of organelles because it’s unnecessary
The normal life of a cell is…
Cyclical, passes through regular stages between one division and the next
What does the cell cycle include?
All stages of interphase and mitosis
Most of the cell’s life is spent…
In interphase, stage between divisions
First factor of interphase in mitosis:
DNA replication
Occurs during S-phase (synthesis)
Second factor of interphase in mitosis:
Significant gap lies between S-phase and mitosis called G2
Third factor of interphase in mitosis:
Another gap from the end of mitosis until onset of next S-phase is called G1
If cell is not going to divide again, it continues in G1 until death
Define asexual reproduction
Reproduction based upon mitotic division of the nucleus and cytokinesis
Offspring genetically identical to parent
Rapid and effective and widely practiced in nature
What is a drawback of asexual reproduction?
Uniformity; leads to production of a clone of genetically identical progeny
Clone may be ill-prepared to survive because it lacks diverse individuals and variations that ensure or heighten adaptability
Adaptability of a population depends upon…
Genetic diversity
First key step in sexual reproduction:
Combination of genetic information from (usually) 2 separate parents
First two steps of combination of genetic information:
1) Each parent provides a sex cell or gamete containing a set of chromosomes
2) Each gamete has a chromosome complement consisting of one copy of each chromosome, we say that the gamete is haploid
Next two steps of combination of genetic information:
3) Two gametes, male sperm and female egg, fuse to produce a single hybrid cell: the zygote or fertilized egg. This fusion is called fertilization or syngamy
4) Zygote contains genetic information from both gametes
Final steps of combination of genetic information:
5) The zygote then has 2 sets of chromosomes, it’s said to be diploid
6) In many species, zygote proceeds to develop by mitotic divisions into a multicellular adult, the body cells produced by mitosis will also be diploid
The process of meiosis consists of…
2 successive nuclear divisions with only 1 cycle of chromosome replication
It is by means of meiosis that a diploid organism can…
Reduce its sex cell chromosome count to the haploid state, enabling the creation of a diploid product of sexual reproduction
Define karyotype
The number, forms, and types of chromosomes in a cell
Most easily observed at metaphase during nuclear division
When a cell is diploid, its karyotype consists of…
Many pairs of chromosomes
In humans, there are normally 23 pairs of chromosomes, or 49 in total
In each pair of chromosomes in a sexually reproducing organism, one chromosome comes from each parent
Define homologous pair
The pair of chromosomes identical in size and shape bearing corresponding, though usually not genetically identical, types of genetic information
A haploid cell will bear…
Only one of the homologues from each pair of chromosomes
Define polyploidy
A condition in which an organism, or given cell, contains a number of complete sets of chromosomes greater than two
Examples of polyploidy
Triploid (3n)
Tetraploid (4n)
Describe the two successive divisions in meiosis
1) Parent cell splits into 2 (homologous chromosomes get separated from each other into different cells)
2) Products then divide again to yield 4 haploid daughter cells (separating sister chromatids)
Define meiosis l
Proceeded by interphase
Each chromosome is replicated
First two important things in prophase l in meiosis l
Nuclear envelope and nucleolus disappear
Centriole pairs migrate in conjunction with formation of spindle
Next important thing in prophase l in meiosis l
Chromosomes condense and synapsis occurs by which homologous chromosomes pair tightly along their entire lengths, thus constituting a bivalent (4 chromatids)
Last important thing in prophase l in meiosis l
Bivalent may be held together by regions in which there appear to be a physical attachments between homologous chromosomes
Regions are called chiasmata
Chiasma reflects an exchange of material between chromatids on homologous chromosomes, geneticists call this crossing over
Describe metaphase l in meiosis l
All of the bivalents have moved to the equatorial plate, spindle fibers have connected to the centromeres, chiasmata have terminalized where present (reached the ends of the chromosomes)
Centromeres of homologous chromosomes orient toward opposite poles
