Mitosis and meiosis Flashcards
Impact of application of genetics to society (6)
- Agriculture (crop improvement)
- Medicine (can scan genetic info to know about disorder than may come later in life)
- Law (stopping immigrants from coming in)
- Sociology
- Philosophy
- Ecology
Organisms and genetic information storing (acellular, prokaryotic, eukaryotic)
Acellular (viruses) - ds or ss DNA or RNA
Prokaryotic (bacteria) - circular, single copy, naked ds DNA
Eukaryotic (animal, plants, fungi, protists) - linear, many copies of histone-bound DNA (not naked)
Sexual cycle - resulting in mixing of DNA from 2 parents in each generation
Human DNA (storage and number of chromosomes)
Stored in chromosomes
23 pairs - 22 pairs of autosomes and a pair of sex chromosomes
What does X,X code for
female
What does X,Y code for
male
What does multicellular organisms depend on cell division for (3)
Development form a fertilised cell
Growth to adult
Repair
Define cell cycle and its 2 major phases
Cell cycle is the lifetime of the cell, depends on the type of cell
Interphase and mitotic phase
Describe interphase and explain the 3 different phases within it
Interphase occurs in between different mitotic stages - it prepares cell for division. Most of the time, the cells are in some part of the interphase
- G1 - all the organelles and cytoplasmic components replicates. Cell grows in size. synthesis mRNA and proteins
- S phase - DNA replication/synthesis occurs. By the end of S phase, each chromosome has been duplicated, containing 2 chromatids. Amount of DNA has been doubled
- G2 - all the enzymes required in cell division are produced
Phases of mitosis
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase (and cytokinesis)
At G2 stage of interphase, what does the cell contain
Duplicated chromatin Centromeres (with centriole pairs) Nucleolus Nuclear envelope Plasma membrane
What phase does the chromosome become visible
prophase
First phase of mitosis (4)
Prophase
- Nuclear envelope breaks down
- chromosomes start to condense
- Nuclear membrane starts to break down
- Aster form around centrosome and aster-covered centrosomes migrate towards opposites of the nucleus in preparation for mitotic spindle formation
Second phase of mitosis (3)
Prometaphase
- The point where spindle fibres grow out of centrioles to the equator of the cell
- Asters are on complete opposite sides of the cell but are connected by microtubules
- begin pushing chromosomes to centre of cell
Third phase of mitosis
Metaphase
- Alignment of chromosomes on the metaphase plate (equator of cell - imaginary) due to growth of spindle fibre
Fourth phase of mitosis
Anaphase
- Kinetochore microtubules connected to the chromosomes shortens and pulls the sister chromatids apart
- Non-kinetochore microtubules lengthen at the same time causing centrosomes to be further apart and splitting the centromeres
- One pole gets one identical copy of each sister chromatid and now called chromosomes
Fifth/last phase of mitosis + cytokinesis
Telophase - Re-formation of nuclear membrane - Chromosomes de-condense - spindle fibres break - nucleus forming - cleavage furrow begins to form in the centre of the cell made from constricting belt of actin filament surrounding the inside of the cell circumference - cytoplasm begins to separate Cytokinesis Separation into 2 cells
Checkpoints
During the cell cycle, certain checkpoints are encountered to make sure the process is occurring accurately
3 checkpoints
G1/S checkpoint - primary checkpoint at which the cell continues or stops. External signals and growth factors can influence the cell cycle and affect the progress at or before this critical checkpoint
G2/M checkpoint - allows cells that have successfully completed all 3 phases of interphase to begin mitosis
Spindle checkpoint - ensuring that all chromosomes have attached to the spindle in preparation in anaphase
Once all checkpoints in interphase are cleared, mitosis can occur
What are the factors in cell cycle regulation that ensues only certain cells divide at certain times
Growth factors, the size of cell and the nutritional state of the cell
Cell division rate
Skin cells = high cell division rate due to wear and tear Other cells (Eg. adult neurons and muscle cells) = low cell division rate
Importance of mitosis accuracy and consistency of checkpoints during interphase
Ensures that most cells in an eukaryotic organism can produce identical copies of themselves
how do single-celled organisms reproduce
by binary fission
Mitosis vs. meiosis (number of replication and products)
Mitosis undergoes 1 replication to form 2 identical daughter cells
Meiosis undergoes 2 replications to produce 4 different cells with half the number of chromosomes
What phase occurs before meiosis I
Interphase (same as mitosis)
- duplication of chromosomes to produce 4 sets of chromosomes
Meiosis I - purpose
separates homologous chromosomes
Prophase I of Meiosis I (3) - difference to mitosis (3)
Chromosomes condense and become visible
Nuclear membrane breaks down/disintegrate
Centromeres moving apart from each other forming spindles
Difference to mitosis
- homologous pairs of chromosomes come together and crossing-over occurs
- Formation of chiasmata where crossing-over occurs between non-sister chromatids
- crossing over occurs away from centromere towards the end of chromosomes
Metaphase I of meiosis (2)- difference to mitosis (1)
- Homologous pairs and chiasmata line up on the metaphase plate
- Pairs of homologous chromosomes attach to kinetochore microtubules through centromeres
Difference to mitosis - Homologous pairs align on metaphase plate in meiosis whereas individual chromosomes line up in mitosis
Anaphase I of meiosis (1) - difference to mitosis (1)
- kinetochore microtubules shorten to pull each homologous pair to each pole
difference to mitosis - In meiosis, the sister chromatids remain attached resulting in homologous paris being pulled to each pole, whereas in mitosis, the sister chromatids are being pulled to each pole
Telophase I & cytokinesis (4) - difference to mitosis (1)
The following does not go to completion
- Reformation of nuclear envelope
- Chromosomes de-condense
- Spindle fibres break
Cleavage furrow formation and cell divides to form 2 cells
Difference to mitosis
- In meiosis, the daughter cells produced here will have 1 copy of the each of the homologues chromosomes and are NOT IDENTICAL. In mitosis, the daughter cells produced are IDENTICAL
Meiosis II - purpose
separate sister chromatids (Same as mitosis)
Prophase II
2 centrosomes connected by spindle in each of the daughter cells
Metaphase II
Sister chromatids connected by kinetochore microtubules and align at metaphase plate
Anaphase II
Spindle fibres pull apart the sister chromatids
- kinetochore microtubules shorten and drag the sister chromatids via the centromere
- Non-kinetochore microtubules lengthen
Telophase II & cytokinesis
- cleavage furrow forms
- produces 4 haploid daughter cells with 1 copy of each of the chromosomes needed
Importance of variation/sex (3)
Changing environments
Spatially variable environments
Reducing sibling-sibling competition for better use of resources
