L2 CELL DIVISION Flashcards
What are the products of Mitosis?
Results in two daughter cells which contain
same number of chromosomes as in parent cell
What are the 4 stages of Mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens during interphase? (5)
1.Growing in size
2.Obtaining nutrients
3.Duplicating cell organelles, cytoplasmic components
4. By copying (replication) its DNA (each chromosome
contains 2 sister chromatids with single centromere)
5.Duplication of centrioles
How long do cells remain in interphase?
Most of its life cycle approx. 23hours.
What are the three phases of interphase and what happens during each?
G1
G2
S
What happens during prophase of mitosis?
Chromosomes begin to coil, become thick and short
-Each chromosome contains 2 chromatids (sister chromatids) joined at the centromere
Centrioles separate and move to the opposite poles of the cell
Parallel running microtubules (spindle fibres) formed and extend between 2 centrioles – spindle formation
Nucleolus disappears
Nuclear envelop disappears and chromosomes are released to cytoplasm
What happens during metaphase of mitosis?
As the nuclear membrane disappears the spindle
occupies the central region of cell
Chromosomes move toward the equator of the spindle and arrange themselves in a line- metaphase plate
Microtubules (spindle fibres) attached to centromeres of chromosomes
What happens during anaphase of mitosis?
Centromeres divide and sister chromatids separate
into individual chromosomes
Spindle fibers contract, the chromosomes are pulled to
opposite poles of the cell
Cleavage furrow is formed at the equator of the cell by in folding of the cell membrane
What happens during teleophase mitosis?
Chromosomes gather at opposite ends of the cell
and nuclear membrane is reformed around them
The spindle disintegrates
Cleavage furrow becomes deep and divides the cell into two (cytokinesis)
What is meiosis?
Special type of cell division which occurs in testes and ovary during the production of sperms and ovum
What does meiosis result in?
Four daughter cells produced at the end of 2 divisions.
Each daughter cell contains half the number (haploid) of parent cell chromosomes
What are the stages of meiosis?
Two divisions occur in quick succession (meiosis I and meiosis II)
What happens during interphase of Meiosis?
Replication (duplication) of DNA takes place
How many phases does Meiosis I have?
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
How many phases does Prophase I of Meiosis have?
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis
What happens during Leptotene phase of Prophase I?
Chromosomes appear as individual threads
Attached at one end to the nuclear envelope
Chromosomes show beads (chromomeres) throughout their length
What happens during Zygotene phase of Prophase I?
Homologous chromosomes come together
Homologous chromosomes pair point to point and called bivalents
These are held together by a fibrillar band called synaptonemal complex
One end connected to nuclear membrane
What happens during Pachytene phase of Prophase I?
Shortening and thickening of chromosomes continue
Two chromatids of a chromosome become visible
Chromatids from 2 chromosomes coil around each other
Exchange of DNA occurs by breaking and rejoining of chromatids – crossing over
What happens during Diplotene phase of Prophase I?
Chromosomes become short and thick
Begin to separate except where the crossing
over has occurred
As the chromosomes become short, the
crossing points become visible
What happens during Diakinesis phase of Prophase I?
Chromosomes become short, thick and get
separated, but homologous chromosomes lie
together
What happens during Prophase I of meiosis?
The centrioles move to the opposite poles of
the cell
– Spindle formation take place between centrioles
– Nuclear envelope disappears and homologous
chromosomes are released to cytoplasm
What happens during metaphase I of mitosis?
As the nuclear membrane disappears the spindle occupies the central region of cell • Paired homologous chromosomes move toward the equator of the spindle and arrange themselves in a line – metaphase plate • Microtubules attached to centromeres of paired chromosomes
What happens during anaphase I of mitosis?
Spindle fibers contract, the paired, homologous chromosomes are pulled to opposite poles of the cell • Cleavage furrow is formed at the equator of the cell by in folding of the cell membrane
What happens during telophase I of mitosis?
Chromosomes gather at opposite ends of the cell
and nuclear membrane is reformed around them
• The spindle disintegrates
• Cleavage furrow becomes deep and divides the
cell into two
• Each cell has 23 chromosomes
• Each chromosome is with 2 sister chromatids
• Each cell has haploid number of chromosomes but
with diploid amount of DNA
Nuclear membrane reforms
What are the 4 stages of Meiosis II?
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
What happens during prophase II of meiosis II?
Centrioles move to opposite poles
Spindle formation takes place
Nuclear envelope disappears and 23 chromosomes
(each with 2 sister chromatids) released to
cytoplasm
What happens during metaphase II of meiosis II?
All 23 chromosomes arrange in a line at the equator
Microtubules (spindle fibres) attached to
centromeres of chromosomes
What happens during anaphase II of meiosis II?
Centromeres split, sister chromatids are pulled to the opposite poles by the spindle fibres
Cleavage furrow is formed at the equator of the cell by infoldings of the cell membrane
What happens during telophase II of meiosis II?
23 chromosomes gather at opposite ends of
the cell and nuclear membrane is reformed
around them
Spindle disintegrates
Cleavage furrow becomes deep and divides the
cell into two
What are the four chromosomal abnormalities that can occur?
Down syndrome (trisomy 21)
Klinefelter syndrome
Turner syndrome (Monosomy X)
What is Down syndrome?
Down syndrome (trisomy 21) is a condition in which a person has an extra chromosome
What is Klinefelter syndrome?
Genetic condition that results when a boy is born with an extra copy of the X chromosome
What is Turner syndrome?
(Monosomy X)
A condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing
