Mitosis and Cell Division Flashcards
Two (2) ways the eukaryotic cells divide
- Mitosis
- Meiosis
Cells that undergo Mitosis
Somatic cells
Cells that undergo Meiosis
Germ cells
What are somatic cells?
Non-reproductive cells
What are germ cells?
Reproductive cells
Decrease in size or wasting away of a body part or tissue
atrophy
Germ cells undergo meiosis to produce __ __.
Haploid gametes
Where are germ cells found?
Reproductive system
The stages of cell cycle
- Interphase
- Mitosis/ Meiosis
- Cytokinesis
What are the phases in the Interphase?
- G1 phase
- S phase
- G2 phase
What happens in G1 phase?
primary growth phase
What happens in S phase?
DNA replication
What happens in G2 phase?
microtubules synthesis
What does the G in G1 and G2 phase mean?
Gap
What happens in the M phase?
chromosomes are pulled apart
What happens in C phase?
cytoplasm divides
What is the longest stage in the cycle?
Interphase
What is the shortest stage in the cycle?
M phase (Mitosis/ Meiosis)
What is the intermediate stage in the cycle?
C phase
The chromosomes are extended and in use
Interphase
- The chromosomes condense
- Nuclear envelope breaks down
- spindle fiber forms
Prophase
chromosomes line up on the central plane of the cell
Metaphase
- centromeres divide
- sister chromatids separate and move toward opposite poles
Anaphase
- chromosomes uncoil
- new nuclear envelope forms
- spindle fibers disappear
Telophase
cytoplasm of the cell is cleaved in half
Cytokinesis
- structure in a chromosome that holds together the two chromatids
- point of attachment of the kinetochore
centromere
cytoskeletal structure of eukaryotic cells that forms during cell division to separate chromatids
spindle fibers/ mitotic spindle (mitosis)/ meiotic spindle (meiosis)
one of the two identical halves of a chromosome that has been replicated in preparation for cell division
chromatid
Who first discovered chromosomes?
Walther Flemming in 1882
How many chromosomes are there in the Australian ant Myrmecia spp.?
1 pair
How many chromosomes are there in some ferns?
500 pairs
How many pairs of chromosomes do humans have?
23 pairs
How do chromosomes exist in somatic cells?
Exist as pairs
- paired chromosomes
- essentially have the same gene sequence, loci (gene position), centromere location, and chromosomal length
Homologous Chromosomes
have two copies of each chromosome: one from mother, one from father
diploid cells
Replicated chromosomes consist of __ __ __.
two sister chromatids
What holds the two sister chromatids together?
centromere
- an individual’s complete set of chromosomes
- a laboratory-produced image of a person’s chromosomes isolated from an individual cell and arranged in numerical order
karyotype
Cells wrap their DNA strands around scaffolding proteins to form a coiled condensed structure called __.
Chromatin
Chromatin is further folded into higher orders of structure that form the characteristic shape of __.
Chromosomes
Components of a chromatin
~40% Complex of DNA
~60% proteins
How many nucleotides does a typical human chromosome contain in its DNA?
about 140 million
What is the equivalent of the 140 million nucleotides in the DNA of a human chromosome?
- about 5cm in stretched length
- 2,000 printed books of 1,000 pages each
Components of a nucleosome
- DNA
- Central histone
What do you call the 30nm spiral of wrapped nucleosomes?
Solenoid
How many sister chromatids do a replicated chromosome consist of?
2 sister chromatids
Difference between sister and non sister chromatids
Sister chromatids - common centromere
Non sister chromatids - different centromeres
The two types of nitrogenous bases
- Pyrimidines
- Purines
What comprises the pyrimidines?
- Cytosine
- Thymine
- Uracil
What comprises the purines?
- Adenine
- Guanine
Supports chromatin loops
Scaffold proteins
packaging proteins of DNA
Histones
What comprises the mitotic spindle?
- polar fibers
- kinetochore fibers
patch of protein found on the centromere of each chromatid
kinetochore
cell division that produces egg and sperm
Meiosis
contain half the complement of chromosomes found in other cells
Gametes
Fusion of gametes is called ___ or ___
- fertilization
- syngamy
fertilization creates the __
zygotes
involves the alternation of meiosis and fertilization
sexual reproduction
does not involve fertilization
asexual reproduction
portion of DNA that control traits
genes
These contain one set of chromosomes
- sperm
- egg cell
This contains two sets of chromosomes
zygote
Meiosis consists of two __ __, but only one __ __
Two successive divisions, but only one DNA replication
What division happens in Meiosis I?
Reductional Division
What division happens in Meiosis II?
Equational Division
separates the homologous pairs
Meiosis I
separates the two sister chromatids of each chromosome
Meiosis II
Stages of Meiosis I
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
Stages of Meiosis II
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
- each duplicated, condensed chromosome pairs with its homologue
- homologues swap segments
- each chromosome becomes attached to microtubules of newly forming spindle
Prophase I
pairing of chromosomes during prophase I
synapsis
swapping of segments of chromosomes
crossing-over
- chromosomes are pushed and pulled into the middle of the cell
- sister chromatids of one homologue orient toward one pole, and those of other homologue toward the opposite pole
- spindle is now fully formed
Metaphase I
- actual division of nucleus
- homologous chromosomes segregate
- sister chromatids of each chromosome remain attached from each other
Anaphase I
- chromosomes arrive at opposite poles
- cytoplasm divides
- two haploid cells, but sister chromatids are still attached
- completes meiosis I
Telophase I
Does DNA synthesis occur in Meiosis II?
No
What are the two main differences of Meiosis II to Mitosis?
- Haploid set of chromosomes (in humans 1n=23 chromosomes)
- Sister chromatids are not identical (crossing-over)
the point of contact, physical link, between two (non-sister) chromatids belonging to homologous chromosomes
Chiasma
new combination of genetic elements
recombinant chromosomes
What are the five (5) stages in Prophase I?
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis
- consists of the condensing of the already replicated chromosomes
- the appearance of chromosomes is likened to ‘a string with beads”
- each sister chromatid is attached to the nuclear envelope and are so close together that they can be mistaken for only one chromosome
- short stage
Leptotene Stage (Leptonema)
one of the serially aligned beads or granules of a eukaryotic chromosome, resulting from local coiling of a continuous DNA thread
Chromomere
- sub-stage where synapsis between homologous chromosomes begins
- these synapsis can form up and down the chromosomes allowing numerous points of contact and can be compared to a zipper structure
Zygotene Stage (Zygonema)
facilitates synapsis by holding the aligned chromosomes together
synaptonemal complex (SC)
After the homologous pairs synapse in Zygotene, they are either called __ or __.
Tetrads or Bivalents
- Once a tetrad has formed, the process of crossing over and the resulting recombination can go ahead
- At this point, the sister chromatids begin to separate from each other, although the chromosomes remain attached as a pair.
Pachytene Stage (Pachynema)
- the two homologous chromosomes begin to migrate apart as the synaptonemal complex disintegrates between the two chromosomal arms and they begin to repel one another.
- chiasma are fully visible at this stage, so can be seen to move towards the end of the chromatids
Diplotene Stage (Diplonema)
The movement of chiasmata at the tip of the chromosome due to condensation
terminalization
- the chiasmata connections arrive at the ends of the chromatid arms of the chromosome
- chromosomes are very condensed and still connected by chiasmata
Diakinesis
What causes andropause?
reduction of hormones (testosterone and dehydroepiandrosterone)
a form of the resting state in which cells reside until they receive appropriate signals stimulating them to re-enter and progress through the cell cycle
G0 phase
When does the no crossing-over happens?
Prophase II
the haploid cell which is formed by the meiosis in spermatocytes
spermatid
Spermatids mature and develop into __ or __
spermatozoa or sperms
What is the process wherein spermatids mature into sperms?
Spermiogenesis
a cell in an ovary which may undergo meiotic division to form an ovum
oocyte
cell giving rise to sperm
spermatocyte
process of formation of female gametes
oogenesis
Spermatogenesis produces __ haploid sperm cells
4 haploid sperm cells
Oogenesis produces __ mature ovum
one mature ovum
byproduct of an oocyte meiotic division
polar body
sexual reproduction increases genetic diversity
evolutionary consequences of sex
What are the three (3) mechanisms that increase genetic diversity?
- Independent assortment
- Crossing over
- Random fertilization
way that homologous chromosomes line up on metaphase plate is random
Independent Assortment
What percentage is the chance that a given member of pair will end up going to a given daughter?
50% chance
As a result of random alignment, the number of possible combinations of chromosomes in a gamete is __.
2^n
What does the n in 2^n signify?
number of chromosome pairs
What is the possible chromosome combinations in humans?
approximately 8 million (8,388,608)
- DNA exchanges between maternal and paternal chromatid pairs
- adds even more recombination to independent assortment
Crossing over
- zygote is formed by the union of two independently produced gametes
random fertilization
What are the possible combinations in an offspring of random fertilization?
more than 70 trillion (70,368,744,177,664)
- does not count crossing-over
Why is generating diversity important?
it is the raw material that fuels evolution
No genetic process generates diversity more quickly than __ __.
sexual reproduction
What is the two (2) unique features of meiosis?
- Synapsis
- Reduction division
homologous chromosomes pair all along their lengths in meiosis I
synapsis
- no chromosome duplication between the two meiotic divisions
- produces haploid gametes
reduction division
