Mitosis/Miosis Flashcards
1
Q
How do new cells arise?
A
- From old cells of the same cell type
2
Q
Why do cells divide?
A
- Growth/differentiation
- Maintenance
- Repair
3
Q
Describe growth/differentiation:
A
Mitosis enables organisms to grow from a single-celled zygote into a mature organism that might contain hundreds of trillions of specialized cells
4
Q
Describe maintenance:
A
New cells produced to replace worn out/dead cells
5
Q
Describe repair:
A
They can regenerate damaged tissues (finger cut -new skin). Some organisms can regenerate entire body parts
6
Q
Somatic cell:
A
A cell that is part of the body (skin, blood)
7
Q
Parent cell:
A
Original call
8
Q
Daughter cell:
A
Newly formed cell
9
Q
Describe cell cycle:
A
- The life cycle of a cell
- Measured from one cell division to the next
- New cells must be able to carry on the functions of the original cell
- Genetic material is central- meaning is must be appropriately divided between cells
10
Q
Describe the arrangement of genetic material:
A
- In a Eukaryotic cell DNA is in a membrane-bound nucleus
- DNA is arranged into chromatin – strands of DNA wrapped around proteins, forms tightly-packed chromosomes during cell division
- Centromere – constricted region in the center of a chromosome
11
Q
Describe the organization of chromosomes:
A
- All somatic cells contain homologous pairs of chromosomes
- one from the mother’s egg (maternal)
- one from the father’s sperm (paternal)
- Human cells have 46 chromosomes total
- Chromosomes are arranged into 22 non-sex homologous (same) pairs
- Homologous pairs are similar in length, gene location and centromere location, and responsible for the same types of characteristics
- These non-sex chromosomes are called autosomes
- The other 2 chromosomes determine sex of an individual (XX, female or XY, male)
12
Q
Describe genes:
A
- Genes are areas of DNA that contain specific information
- Location of genes is locus
- Alleles – slightly different versions of the same gene on homologous chromosomes
13
Q
Describe diploid cells:
A
cells have pairs of homologous chromosomes, eg. Human somatic cells (46 chromosomes)
14
Q
Describe haploid cells:
A
Haploid cells have no pairs, eg. Human gametes (23 chromosomes)
15
Q
Define polyploid:
A
some organisms have more than two sets of homologous chromosome
16
Q
What is a karyotype?
A
- Arrange stained chromosomes from a dividing cell into homologous pairs
- Can use this to check for differences/abnormalities which could infer a genetic disorder
17
Q
Describe the stages of the cell cycle:
A
- Interphase: growth stage- consists of G1, S & G2
G1: cell growth (organelle replication)
- DNA = 46 single strands of unreplicated chromatin - S: synthesis phase- DNA is replicated
- 46 single 46 double strands of chromatin
- G2: 2nd growth stage
- rebuild energy reserves & preparation for ÷ - Mitosis: ÷ of genetic material & nucleus
- Cytokinesis: ÷ of the cytoplasm & organelles
18
Q
Describe the growth phase:
A
- Also called Interphase
- This is where a cell spends most of it’s life
- Carries out regular functions and prepares for next division
- Three phases: G1, S and G2
19
Q
Describe the G1 phase:
A
- Rapid cell growth during this phase
- Normal cell activities
20
Q
Describe the s phase:
A
- Mid-way through interphase
- DNA copied exactly
- Creates identical chromosomes, called sister chromatids, joined at centromere
21
Q
Describe the G2 phase:
A
- Cell rebuilds energy supplies to prepare for cell division
- Cell manufactures proteins and other
materials needed for cell division
22
Q
Describe the cell division stage:
A
- Two main process:
- Mitosis – division of genetic material and nucleus into two sets
- Cytokinesis – division of cytoplasm and organelles into two sets
23
Q
A
24
Q
Define mitosis:
A
Cell division in somatic cells
25
Q
Describe mitosis:
A
- All of the cells produced by mitosis are IDENTICAL in genetic makeup to the original cells (particularly important is that the chromosome # doesn’t change)
- The unique appearance and functionality found in different cells of the body (except the sex cells) is NOT due to difference in cellular content, but a difference in the way that content is expressed (differentiation)
26
Q
What are the phases of mitosis?
A
- Prophase
- Metaphase
- Anaphase
- Telophase
27
Q
Step 1: prophase
A
- Chromatin condenses into chromosomes
- Nuclear membrane breaks down
- nucleolus becomes invisible
- Centrioles (organelles active during cell division) move to opposite poles of cell – create a spindle apparatus in the process
- Spindle fibres are made of microtubles – help chromosomes move through cell
28
Q
Step 2: metaphase
A
- Spindle fibres attach to centromeres
- Spindle fibres guide chromosomes to equator (center) of cell
- Chromosomes are aligned so that one sister chromatid is facing each pole
29
Q
Step 3: anaphase
A
- Centromere splits, sister chromatids separate
- Spindle fibres shorten and pull sister chromatids to opposite poles (other spindle fibres lengthen to push and help the process)
- One set of chromosomes now at each pole
30
Q
Step 4 - telophase
A
- Chromosomes unwind into chromatin
- Spindle fibres break down
- Nuclear membrane forms around chromosomes
-Nucleolus forms within nucleus
31
Q
Mitosis in plant cells:
A
- Plants to not have centrioles, but do form spindle fibres
32
Q
Describe the mitotic index:
A
- The ratio of cells undergoing mitosis to the total number of cells in a population
- Calculate by #cells in mitosis/# total cells
33
Q
Define cytokinesis:
A
Division of cytoplasm
34
Q
Describe cytokinesis in animal cells:
A
- Indentations in membrane form and deepen until cell is pinched in two
- Cytoplasm and organelles divide equally between two halves
35
Q
Describe cytokinesis in plant cells:
A
- Cell wall cannot “pinch” so cell plate is formed
- Cell plate is a membrane that forms between the two new cells, reinforced with cellulose to make new cell wall
36
Q
When does interphase occur?
A
Before and after mitosis
37
Q
Describe how cancer works:
A
- Cells must divide only at certain times in healthy individual
- Cancer occurs when cell cycle is accelerated, cancer cells spend very little time in interphase
- Interphase is the phase when cells are performing normal functions
- Cancer cells divide uncontrollably
38
Q
Describe cloning:
A
- Clone = genetically identical organism derived from a single parent cell
- Replace a haploid nucleus of an egg with a diploid nucleus
- Dolly the sheep – nucleus from mammary tissue of one cell was placed into the egg of another sheep
- She died prematurely
- Many plant species and some animal species have natural methods of cloning. (eg. vegetative reproduction)
- Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells.
- Methods have been developed for cloning adult animals using differentiated cells.
39
Q
Describe somatic cells in meiosis:
A
- Somatic cells have DNA from maternal and paternal sides combined —> diploid = 2n
– e.g., Humans have 23 differente.g., Humans have 23 different chromosomes, therefore 2(n) = 462(23) = 46
40
Q
Describe gamete cells in meiosis:
A
- Gametes (sperm or eggs) only hold half the DNA from somatic cells from which they came —> haploid = n
e.g., Humans have 23 different chromosomes, therefore n = 23
41
Q
Describe Meiosis:
A
- Creates gametes
- Reduces chromosome number from 2n —> n by copying chromosomes once, but dividing twice
- First division, meiosis I, separates homologous chromosomes
- Second, meiosis II, separates sister chromatid
42
Q
Describe interphase in meiosis:
A
- Same process as cells undergoing mitosis
43
Q
Step 1: prophase 1 in meiosis:
A
- Chromatin —> chromosomes, nuclear envelope disappears
- Pairs of homologous chromosomes line up side by side
- End up with four chromatids together (joined at centromere in twos) called a tetrad
- The chromosomes in this tetrad are very similar but not identical
- Allows “crossing over” to occur (see later notes)
44
Q
Step 2: metaphase 1 in meiosis:
A
- Tetrads (homologous pairs) that formed in Phrophase I are lined up along equator –> centromeres on either side of equator
- Spindle fibres attach to centromeres
45
Q
Step 3: Anaphase I in meiosis:
A
- Homologous pairs separate (not sister chromatids) at the centromere
- Centromeres do not split
- Tetrad is separated so that a chromosome goes to each pole (pulled by spindle fibres) – (segregation)
- There should be 23 double chromosomes at each pole (sister chromatids remain intact)
46
Q
Step 4: Telophase I in meiosis:
A
- Not all cells go through telophase I, some go straight to Prophase II
- Many cells DO NOT uncondense the chromosomes, however in some cells, chromosomes do uncoil
- Spindle fibres disappear and two new cells are formed (each with one set of the homologous chromosomes).
47
Q
Step 5 in meiosis:
A
Cytokinesis occurs
48
Q
Step 6: Prophase II in meiosis:
A
- Begin with new haploid cells from meiosis
- Centrioles move to opposite poles
- Spindle fibres re-form (as well as chromosomes if necessary)
(Meiosis II is very similar to Mitosis)
49
Q
Step 7: Metaphase II in meiosis:
A
- Cell moves directly to metaphase —> no DNA replication and no formal organization of nucleus
- Looks like metaphase in mitosis
- Chromosomes line up along equator
- Spindle fibres are attached to each centromere
50
Q
Step 8: Anaphase II in meiosis:
A
- Spindle fibres shorten —> chromatids separate at centromeres
- Centromeres split and sister chromatids are pulled/pushed to opposite poles
- There should be 23 single stranded chromosomes/chromatids at each pole
51
Q
Step 9: Telophase II in meiosis:
A
- End up with four cells (from original one)
- Chromosomes unravel and nuclear membrane is formed
52
Q
Step 10 in meiosis
A
Cytokinesis occurs
53
Q
Describe oocytes:
A
- In oocytes, meiosis I is put on hold at the end of prophase I until the girl reaches puberty, when meiosis I will complete
- Meiosis II is completed if the oocyte becomes fertilized
54
Q
Describe gametogenesis:
A
- The formation of ova and sperm follow the process of meiosis, specializations dependent on their function
- Sperm are designed for movement (little cytoplasm), lots of cell division, produce 4 small sperm
- Eggs are designed to nourish the zygote – only one ovum is produced per oocyte —> the other 3 polar bodies sacrifice their cytoplasm to produce one large egg
55
Q
Describe non-disjunction:
A
- Caused by unequal chromosome division (usually in anaphase II but could be anaphase I)
- Resulting gametes have too many or too few chromosomes
- Offspring produced by these gametes can have trisomy (three copies of a chromosome) or monosomy (one copy)
- Results in abnormalities or even miscarriage
56
Q
What are the sources of genetic variation:
A
- Independent assortment
- Crossing over
57
Q
Define recombination:
A
Making new combination of genetic material
58
Q
Describe independent assortment:
A
- Since first process is to split up the homologous pairs, end up with a slightly different chromatid in each of the four new cells
- Also, may end up with a mixture of homologous chromosomes of maternal and paternal origin facing each pole in metaphase I
59
Q
Describe crossing over:
A
- When non-sister chromatids are side-by-side (when homologous pairs lined up) they may exchange genetic material
- Even if a small section crosses, over, thousands of genes may be transferred.
60
Q
Describe polyploidy:
A
- nondisjunction is actually a desired characteristic in the development of large luscious fruit – big strawberries might be 4n or even 6n (polyploidy)
- An estimated 30-80% of living plant species are polyploid
61
Q
Describe spermatogenesis:
A
- Diploid germ cell is a “spermatogonium”
- Spermatogonium form two daughter cells by mitosis
- One of the two daughter cells develops into a primary spermatocyte
- Primary spermatocyte undergoes meiosis I, forms two secondary spermatocytes
- Secondary spermatocyte forms two spermatids (develop into sperm)
62
Q
Describe oogenesis:
A
- Start with diploid oogonium
- Oogonium undergoes mitosis to form two primary oocytes
- Oocytes remain arrested (stalled) at prophase I until puberty
- Each month, one oocyte undergoes meiosis
- Uneven division of cytoplasm – one that receives most is secondary oocyte, other is first polar body
- Secondary oocyte undergoes meiosis II, unequal cytoplasm division again —> mature egg (other is second polar body)
- Polar bodies disintegrate
- Secondary ooctye arrested at metaphase II until fertilization
63
Q
Describe how twins work:
A
- Fraternal – more than one secondary oocyte produced in a month, both are fertilized
- Identical – single fertilized zygote divides into two bodies within the first few days of embryonic development
64
Q
Describe reproductive strategies: Prokaryotes
A
- No nucleus
- Single, circular chromosome
- Binary fission (asexual) – chromosome doubles and is separated between two new cells
- Conjugation – transfer of genetic material from one bacteria to another via a bridging structure (pilus)
65
Q
Describe reproductive strategies: asexual reproduction
A
- Budding – a complete but miniature version of the parent grows from the parent’s body
- Vegetative reproduction – similar to budding but usually involves plants sending runners with a new plant on the end
- Fragmentation – process of creating a new organism from a fragment of the other
- Parthenogenesis – unfertilized egg develops into an adult
- Spores – small structure containing genetic material (not always asexual)
66
Q
Describe alterations of generations:
A
- Occurs in plants
- Plants have a diploid and a haploid generation
- Would be like an egg or sperm having a life of it’s own
- Diploid generation is sporophyte
- Haploid generation is gametophyte
- Whether the “plant” is a sporophyte or gametophyte depends on the type of plant
67
Q
Describe alteration in sexual cycles:
A
- Animals don’t have alternation of generation
- Some, such as jellyfish, have a stage that can reproduce asexually and one that can reproduce sexually
68
Q
Describe karyotyping:
A
- Performed using cells collected by chorionic villi sampling or amniocentesis
- Analyze chromosomes to determine gender or see if non-disjunction has occured
69
Q
Define a karyogram:
A
A graphical representation of a karyotype
70
Q
Define a karyotype:
A
A property of a cell showing the number and type of chromosomes present
