Unit 8-Cell Division Flashcards
Define cell division
Reproduction of a cell that results in two daughter cells that are genetically identical to each other and to the original parent cell
What are chromosomes
The structures that contain most of the cells DNA
It is split into two during cell division.
Define asexual reproduction
The creation of genetically identical offspring by a single parent without the participation of sperm and egg
Define sexual reproduction
It requires fertilization of an egg by a sperm
The production of gametes involves a special type of cell division that occurs only in reproductive organs
Offspring resemble parents but not identical
Define mitosis
One mother cell producing two daughter cells
Genetically identical
Same number of chromosomes
Happens in all eukaryotes
Define meiosis
One mother cell divides into 4 products Genetically unique Half as many chromosomes Happens only in specialized structures of certain eukaryotes Produces spores eggs or sperm
What are the three functions of cell division
Reproduction
Growth
Repair
Explain DNA organization
Chromosomes (X)
The coiled fibres are chromatin
DNA is wrapped around a Histone
How do prokaryotes reproduce
Binary fission
What is binary fission
What type of reproduction is it
Cell divides in half
Asexual
What are sister chromatids and what are they held together by
Duplicated chromosomes which contain identical copies of the DNA molecule
Held together by the centromere
When does a chromosome consist of two identical chromatids
When the cell is preparing to divide and has duplicated its chromosomes but before the duplicates actually separate
Explain the cell cycle
An ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division into two cells
How is the DNA packaged in a working cell (interphase)
Chromatin
How is DNA packaged during cell division (M phase)
Chromosomes
Define interphase
What most of the cell cycle consists of Cells metabolic activity is high and the cell preforms various functions Periods of growth DNA replication Preparation for mitosis
Define the mitotic phase (M phase)
The part of the cell cycle when the cell actually divides
Nuclear division
Define cytokinesis
Begins before mitosis ends
The cytoplasm is divided in two
Cell division
Explain the stages of interphase
G1
-organelle expansion and cell growth
S phase
- DNA synthesis when chromosomes duplicate
G2
- mitochondria and chloroplasts growth centrosome divides
G0
- typical cell functions; respiration working and moving
What do we start with in mitosis
One cell with one nucleus
Two copies of each chromosome (chromatids)
What do we end with in mitosis
Two nuclei
Each with one copy of each chromosome
Where are the chromosomes during mitosis
In the nucleus
Where are the centrosomes during mitosis
In cytoplasm
Explain prophase
The chromatin fibres become more tightly coiled into chromosomes as sister chromatids
The mitotic spindles begins to form from the centrosomes
Centrosomes move away from each other
Explain pro-metaphase
The nuclear envelop breaks into fragments and disappears
Microtubules and centrosomes move to opposite poles and the mitotic spindles reach for the chromosomes
Mitotic spindles attach to kinetochore
Explain metaphase
Mitotic spindles are attached to chromosomes and they are moved to the centre or metaphase plate
Explain anaphase
The two centromeres of each chromosome come apart separating the sister chromatids
Move to each pole with an equivalent and complete set of chromosomes
Explain telophase
The cell continues to elongates
Daughter nuclei appear at the two poles
Nuclear envelope begins to form around chromosomes
Chromatin uncoils from the chromosome shape and mitotic spindles disappear
Explain cytokinesis
The division of the cytoplasm
When the two daughter cells completely separate
Define the cleavage furrow
A shallow indentation in the cell surface
Happens in animal cells
Define cell plate
A membranous disc
Grows outward
Happens in plants
What happens when cytokinesis doesn’t occur
Results in a bigger cell with two identical nuclei
Yellow slime mould and muscle cells- lives as large multinuclei complexes
Define syncytium
Organisms that live as a very large cell containing multiple nuclei
Define the cell cycle control system
A cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle
Checkpoints in cell cycles
A critical control point where stop and go signals can regulate the cycle
What checkpoint in the cell cycle is seen as the most important
G1 checkpoint
Because if given go ahead it goes into cell division stages but if not then it goes into G0 where the cell doesn’t divide
What are the requirements of the G1 checkpoint
Is the cell large enough
Does the cell have enough nutrients
Is the DNA undamaged
Have the growth factors signalled
What are the requirements of the G2 checkpoint
Before the M phase
Must have successful DNA replication and undamaged DNA
What are the requirements of the metaphase checkpoint
Happens before anaphase
Spindle fibres have to attach and ensure equal distribution
What is a tumour
An abnormally growing mass of body cells
Define benign tumours
When abnormal cells remain at the original site (are contained)
Can cause problems if they grow in and disrupt certain organs
Define malignant tumours
Can spread into neighbouring tissues (cancerous)
Define metastasis
The spread of cancer cells beyond their original site
How are chromosomes arranged in meiosis
As homologous pairs
Define homologous pairs
Two matching chromosomes
Same genes but maybe in different forms
Define the locus
The particular place a gene is located to code for a specific trait such as freckles and is found on the chromosome
How many chromosomes in humans
How many pairs of chromosomes in humans
46
23
Are all of your chromosomes fully homologous
If you are a female then yes
If you are a male then no
- your sex chromosomes are only partly homologous
Define sex chromosomes
Define autosomes
The chromosomes that determines an individuals sex
The other 22 pairs of chromosomes are called autosomes
Define somatic cells
Body cells
Are somatic cells diploid or haploid
Diploid cells 2N
Two complete sets
Homologous pairs
Two copies of each gene
Are sex cells haploid or diploid
Haploid 1N
Half as many chromosomes
One copy of each gene
A fertilized egg is called what
A zygote
Is a zygote haploid or diploid
Diploid
Has two sets of chromosomes
One set from each parent
Define meiosis
A type of cell division that produces haploid cells in diploid organisms
If it weren’t for meiosis each generation would have twice as much genetic material as the generation before
explain interphase during meiosis
similar to mitosis; at the end of interphase each chromosome consists of two genetically identical sister chromatids and the centrosome also duplicates
explain prophase 1
chromatin coils up to form chromosomes
synapsis occurs which is when homologous chromosomes come together into pairs which is called a tetrad
crossing over occurs
centromeres move apart spindle fibres produce and nuclear envelope dissolves
explain metaphase 1
chromosome tetrads align in the center
homologous chromosomes are linked together by crossing over
explain anaphase 1
the chromosomes move towards the two poles
the sister chromatids stick together and only the homologous chromosomes split and move across
explain telophase 1
the chromosomes arrive at the opposite ends and still consist of two sister chromatids
explain cytokinesis after telophase 1
usually cytokinesis occurs after telophase 1 and two haploid daughter cells are formed
sometimes the chromosomes uncoil and the nuclear envelop reforms
is there a interphase after meiosis 1
in some yes in others daughter cells produced divide immediately
in either case NO chromosome duplication occurs between telophase 1 and the beginning of meiosis 2
explain prophase 2
a spindle fibre forms and moves the chromosomes toward the middle
explain metaphase 2
the chromosomes align at the middle and begin to be pulled to the opposite sides
explain anaphase 2
the centromeres of sister chromatids finally separate and the sister chromatids of each pair are now individual daughter chromosomes and move to opposite sides of the poles
explain telophase 2
nuclei form at the cell poles and cytokinesis begins as well
after meiosis 2 what are the results
four daughter cells each with the haploid number of (single) chromosomes
is meiosis 2 the same as mitosis
basically yes
a cell has the haploid number of chromosomes but each chromosome has two chromatids. the chromosomes are arranged singly at the center of the spindle. what is the meiotic stage
metaphase 2
what do we start with in meiosis
one cell with one nucleus
two copies of each homologous pair of chromosome (tetrad)
what do we end with in meiosis
four cells
each with one copy of one of the homologous chromosomes
where are the chromosomes during meiosis
the nucleus
where are the centrosomes during meiosis
the cytoplasm
compare mitosis and meiosis - DNA replication
for both mitosis and meiosis the chromosomes duplicate only once during S phase
compare mitosis and meiosis - number of cell divisions
mitosis- one division of the nucleus
meiosis - two nuclear and cytoplasmic divisions
compare mitosis and meiosis - products
Mitosis - produces two identical diploid cells
meiosis - produces four haploid cells
define crossing over
an exchange of corresponding segments between non-sister chromatids of homologous chromosomes
what is a chiasma
the place where two homologous chromatids are attached to each other
define genetic recombination
the production of gene combinations different from those carried by the original parental chromosome
what is a karyotype
a photographic inventory of an individuals chromosomes
an ordered display of magnified images of an individuals chromosomes arranged in pairs
what is trisomy 21
an extra copy of chromosome 21 that causes down syndrome
what is nondisjunction
an occasional mishap in which the members of a chromosome pair fail to separate
explain how nondisjunction could result in a diploid gamete
a diploid gamete would result if the nondisjunction affected all the chromosomes during one of the meiotic divisions
Animal life cycle
Start with a diploid(somatic cells)multicellular animal
Gamete production
- by meiosis
- occurs within gonads
- produces haploid cells (sperm and egg)
Fertilization
- forms a diploid zygote
Fungus life cycle
Starts with multicellular fungus
The haploid structure grows from the spores
Gamete production
- by mitosis
- produces single haploid cells
Fertilization
- forms a diploid zygote
- then divides by meiosis which forms haploid spores
Plant life cycle
Starts with multicellular plant that is diploid
Produces haploid spores by meiosis
Spores germinate creating a haploid multicellular plant
Produces haploid gametes by mitosis
Fertilization creates a diploid zygote
