Mitosis & Meiosis Flashcards
What are the 6 stages of the cell cycle?
- interphase
- prophase
- metaphase
- anaphase
- telophase
- cytokinesis
What are the 8 phases of meiotic cell division?
- prophase I
- metaphase I
- anaphase I
- telophase I & cytokinesis
- prophase II
- metaphase II
- anaphase II
- telophase II & cytokinesis
What are the 8 phases of meiotic cell division?
- prophase I
- metaphase I
- anaphase I
- telophase I & cytokinesis
- prophase II
- metaphase II
- anaphase II
- telophase II & cytokinesis
How many chromatids does a human somatic cell contain after interphase but before mitosis?
92
What event occurs in prometaphase of mitosis?
the nuclear envelope fragments
What event occurs in prometaphase of mitosis?
the nuclear envelope fragments
T or F: the nuclear envelope fragments in prometaphase of mitotic division in both eukaryotic phytoplankton and most other eukaryotes?
FALSE. the nuclear envelope fragments in most eukaryotes but remains intact in diatoms and dinoflagellates
Define heredity
transmission of traits from one generation to the next
Define genetics
the study of heredity and the variation of inherited characters
Genetics are the inherited properties or features of an organism
Define gene
A unit of hereditary information consisting of a specific nucleotide sequence in DNA
Genes specify the organism’s inherited traits
Define genome
A cell’s complete set of DNA
Define allele
Alternative version (variation of) a gene that may produce a visible difference (phenotypic effect)
ex. Hair colour
Define sex chromosome
Chromosomes that determine the sex of an organism
- either XX or XY
Define somatic cell
All cells of the body except gametes and their precursor cells
How is genetic material organized in prokaryotic cells?
The genome is often a single, circular DNA molecule located in the nucleoid
How is genetic material organized in eukaryotic cells?
The genome usually consists of a number of linear DNA molecules located in the nucleus and mitochondria (and chloroplasts of plant cells)
Define karyotype
An ordered display where homologous chromosomes are arranged by length in pairs
How many pairs of autosomes do humans have?
22
Define sister chromatid
Joined identical copies of the original chromosomes
Define homologous chromosomes
A pair of chromosomes that are of similar length, staining pattern, and centromere location, but may have different varieties of a gene (different alleles)
One of the chromosomes come from the biological mother’s egg; one from the biological father’s sperm
T or F: all humans have at least one X sex chromosome, but not all humans have Y chromosomes?
TRUE
Define gene locus
The location of a gene on a chromosome
When are chromosomes uncondensed? What form do they take during this period?
Are they visible at this time?
When cells are not dividing
Chromosomes are in the form of long, thin chromatin fibres (even when replicating)
NOT visible
When do chromosomes start to condense/coil? Are they visible at this time?
After replication, when they are heading into mitosis or meiosis
They are visible
T or F: after DNA replication, each duplicated chromosome is composed of 2 sister chromatids
TRUE
What protein holds together sister chromatids along their lengths?
Cohesins
Define cohesin
A protein complex that helps regulate the segregation of the sister chromatids during cell division
They hold together the two sister chromatids to form one chromosome until they’re ready to be separated
Define centromere
The region on each sister chromatid where the sister chromatid is most closely attached to its sister chromatid
What are the two kinds of nuclear cell division?
Mitosis and Meiosis
Define cytokinesis
The process of the cytoplasm (the rest of the cell) being divided that usually co-occurs during the Telophase stages of mitosis and meiosis when the daughter cells are produced
Define cytokinesis
The process of the cytoplasm (the rest of the cell) being divided that usually co-occurs during the Telophase stages of mitosis and meiosis when the daughter cells are produced
What are the 2 phases of a somatic cell?
Mitotic phase alternates with interphase in the cell cycle
Describe interphase
The longest phase of a cell’s life (~90%), when a cell grows and copies its chromosomes BEFORE mitosis or meiosis. It is also the time when a cell performs its functions
What are the 3 subphases of interphase and what occurs during each?
- G1: cell grows
- S: chromosomes are duplicated (synthesis) and cell grows
- G2: cell grows
During all subphases, cells grow by producing organelles and proteins
Define mitosis
The division of the nucleus of a eukaryotic cell so that the two resulting daughter cells have the identical genetic information as each other and the parent
What are the functions of mitosis?
Asexual reproduction in unicellular organisms
Asexual reproduction, growth, repair, and cell replacement in multicellular organisms
T or F: Plants use mitosis to produce gametes
TRUE
Give a brief summary of mitosis in animal cells
Chromosomes will condense, be organized in the centre of the cell and then the chromatids will be pulled to opposite ends of the cells and the cell will cleave and be split into two identical daughter cells
What 4 events occur in G2 of interphase in animal cells?
- nuclear envelope is present
- nucleoli are present
- chromosomes are duplicated but NOT condensed
- two centrosomes have formed from one centrosome (each contains two centrioles)
Define centrosome
A subcellular region that contains material that organizes the cell’s microtubules
Define microtubules
Fibres that attach to the chromosomes to separate the sister chromatids or homologous chromosomes
Define centrioles
Located at the centre of the centrosome but are not necessary for the microtubule formation, they just help organize the microtubules
T or F: plant cells do not have centrioles. Why/Why not?
TRUE. the nuclear envelope seems to do the job of organizing microtubules instead
T or F: plant cells do not have centrioles. Why/Why not?
TRUE. the nuclear envelope seems to do the job of organizing microtubules instead
What 9 major events occur during prophase of mitosis in animal cells?
- Chromosomes condense
- nucleoli disappear
- sister chromatids are linked together by cohesins
- cytoskeleton disappears
- mitotic spindle begins to form
- centrosomes move away from each other towards poles
- nuclear envelope fragments
- sister chromatids both have kinetochores
- spindle fibres connect to some of the kinetochores
Describe the mitotic spindle
Composed of centrosomes and microtubules
Define kinetochore
A structure of proteins associated with the centromere. Where the spindle fibres attach
Describe the 3 events that occur during metaphase of mitosis
- the centrosomes are at opposite ends of the cells
- the chromosomes are arranged at the metaphase plate (equal distance between the two centrosomes)
- Spindle fibres are attached to all the chromatid kinetochores
Describe the 4 events that occur during anaphase of mitosis
- cohesins are cleaved by the enzyme separase so the sister chromatids can separate
- chromosomes (each individual sister chromatid) move to opposite ends of the cell towards centrosomes because the attached microtubules shorten
- microtubules that are not attached to the kinetochores lengthen and elongate the cell
- each chromosome
(containing equivalent and complete complement of original chromosome) reach opposite ends of the cell
Describe the events that occur during telophase of mitosis
- daughter nuclei form
- nuclear envelope reforms
- nucleoli reappear
- chromosomes become less condensed
- spindle microtubules disappear
- cytoskeleton reappears
- cytokinesis co-occurs
What occurs during cytokinesis in mitotic division of animal cells? And when does cytokinesis occur?
Cytokinesis is the division of the cytoplasm that co-occurs during telophase
The cell membrane pinches in cleavage to separate the two nuclei into two genetically identical daughter cells
How does cytokinesis differ in plant cells?
A cell plate grows between the two nuclei (instead of a cell membrane) and grows into a cell wall to split the daughter cells
Which process is used by prokaryotes to conduct cell division?
Binary fission
Describe binary fission
The process in which prokaryotic cells divide. During which cells grow to roughly double their size and divide to form two cells
Which process is used by prokaryotes to undergo cell division?
Binary fission
Describe binary fission
The process in which prokaryotic cells divide. During which cells grow to roughly double their size and divide to form two cells
T or F: Binary fission includes mitosis. why/why not?
FALSE.
Mitosis is the division of the NUCLEUS; prokaryotes do NOT have nuclei so therefore they cannot undergo mitosis
How long can DNA of a prokaryotic cell be in comparison to the size of the cell?
Can be 500x the length of the cell, highly coiled and folded
What are the 5 events of binary fission?
- DNA replication begins
- Cell elongates during replication (After replication, cell is about 2x larger)
- Cell membrane pinches inward
- Divides one cell into two identical daughter cells, each with a complete genome
Define meiosis
The division of a eukaryotic, diploid cell’s nucleus that reduces the genetic complement of the four daughter cells to haploid
T or F: meiosis produces 4 genetically identical daughter cells
FALSE.
Meiosis produces 4 genetically UNIQUE daughter cells
When does meiosis occur?
When an animal cell needs to produce gametes
When a plant cell needs to produce spores
Where does meiosis occur in animal cells and plant cells?
Animal cells: in the gonads (testes and ovaries) of complex animals
Plant cells: in the ovules and pollen grains of angiosperms and gymnosperms
What is the function of Meiosis?
it is used ONLY for sexual reproduction
Define a diploid cell
A cell with two sets of chromosomes
How many chromosomes will a diploid human cell have?
2 sets of 23 chromosomes = 46 total
Can a diploid cell undergo mitosis AND meiosis?
Yes
Define a haploid cell
A cell with only one set of chromosomes
How many chromosomes will a human haploid cell have?
1 set of 23 chromosomes = 23 total
Can a haploid cell undergo mitosis AND meiosis?
NO, can ONLY undergo mitosis
Define a gamete
A single cell that transmit genetic information to the next generation
Either a sperm cell or an egg cell
Define fertilization
the process in which a sperm and egg unite to form a zygote that contains the genetic information from both parents
Define a spore
A haploid cell that is produced by the diploid multicellular stage of plants
What events occur during prophase I of meiosis?
- Chromosomes begin to condense
- Homologous pairs become physically connected along their length by a protein complex (synapsis)
- genetic material is exchanged between each pair of homologous chromosomes via crossing over
- Synapsis ends when protein complex (synaptonemal complex) that held homologs together is disassembled (chiasmata and cohesins still hold them together)
- Homologs now move a slight distance away from each other
- Centrosomes move towards poles
- Cytoskeleton breaks down
- Spindle forms
- nuclear envelope breaks down
- Microtubules attach to some kinetochores
Define crossing over
An event that occurs during Prophase I of meiosis in which the joined HOMOLOGOUS chromosomes swap genetic material
Does crossing over occur between homologous chromosomes or sister chromatids? Why?
Homologous pairs
Because sister chromatids are identical copies, so they would be swapping the same genetic material
Homologs are composed of a chromosome from the mother and a chromosome from the father, so they will contain different alleles and the genetic information swapped will be different
Define chiasmata
The location where the homologous chromosomes cross over genetic information
What events occur during metaphase I of meiosis?
- pairs of homologous chromosomes are arranged at the metaphase plate (one chromosome in each pair is facing a different pole)
- Independent assortment
- all microtubules attach to all the kinetochores
- spindle fibres from both poles attach to the chromatid closest
Define independent assortment
During metaphase I of meiosis I, homologous pairs are positioned along the metaphase plate independently of each other and there is a 50% chance the daughter cell will get the maternal or paternal chromosome from a pair
How is the number of possible chromosome combinations from independent assortment determined?
Give an example of human gametes
By 2^n where n= haploid number of the organism
ex. 2^23 = ~8.4 million possible combinations of homologous pair arrangements on the metaphase plate during independent assortment
What is the purpose of independent assortment?
Helps generate the genetic diversity in sexual reproduction
What events occur during anaphase I of meiosis?
- enzyme Separase cuts the cohesins between the sister chromatids to separate homologs (but cohesin persists at the centromere between sister chromatids so they move together)
- homologs guided by spindle fibres towards opposite poles
What events occur during telophase I of meiosis?
- each half cell has a haploid set of chromosomes
- each chromosome is still composed of two sister chromatids
- nuclear envelope reappears
- cytokinesis occurs to yield two haploid daughter cells
T or F: After telophase I and cytokinesis of meiosis I, DNA is replicated before going into meiosis II or interphase
FALSE. DNA is NOT replicated after meiosis I
What events occur during prophase II of meiosis?
- Spindle apparatus forms
- chromosomes begin to move to metaphase plate
(this occurs in both of the two genetically unique daughter cells produced in meiosis I)
What events occur during metaphase II of meiosis?
- chromosomes are positioned at the metaphase plate
- crossing over occurs between sister chromatids because they are no longer identical
- spindle fibres from opposite poles are attached to kinetochores of chromatids
What events occur during anaphase II of meiosis?
- chromatids separate when the cohesins holding them together break down
- chromatids move toward opposite poles and are now individual chromosomes
What events occur during telophase II of meiosis?
- nuclei reforms
- chromosomes begin decondensing
- cytoskeleton reforms
- spindle fibres break down
- cytokinesis occurs
- 4 haploid daughter cells are produced that are genetically unique from one another and the parent cell
What are the 3 origins of genetic variation in the offspring of sexual reproduction?
- independent assortment of chromosomes in metaphase I of meiosis
- crossing over in prophase I of meiosis
- Random fertilization
Approximately how many possible genetic combinations can a single zygote of two human parents have?
~70 trillion
What is one major similarity between mitosis and meiosis?
DNA replication occurs during interphase before either of the cell division processes begin
What are 4 major differences between mitosis and meiosis?
- In mitosis, there is only one division. Whereas in meiosis, the cell divides twice (although both use the same phases: PMAT)
- In mitosis, synapsis of homologous pairs does not occur. In meiosis, synapsis of homologous chromosomes occurs during prophase I (along with the crossing over between nonsister chromatids = chiasmata holding the pairs together due to sister chromatid cohesion)
- Mitosis produces 2 diploid, genetically identical daughter cells. Meiosis produces 4 haploid, genetically unique daughter cells
- Mitosis functions in asexual reproduction of unicellular and multicellular organisms, and produces cells for growth and repair in MC. Meiosis functions in producing gametes for sexual reproduction and is the reason for genetic variability
