4.2 Mitosis and Meiosis Flashcards
What happens in prophase?
-centrioles separate and move to opposite sides of
nucleus
-sister chromatids attach to spindle fibres
-nucleolus disappears and nuclear envelope starts to break down
What happens in metaphase?
-sister chromatids fully attached to spindle fibres
-spindle fibres move them to middle of cell
What happens in anaphase?
-sister chromatids separate from their partners to
become individual chromosomes
- spindle fibres pull chromosomes to opposite ends of
cell
What happens in telophase?
-chromosome–> chromatin
-spindle fibres disappear
-nuclear envelope reforms around each set of daughter chromosomes
What is the function of the spindle during
mitosis?
Equally divides the chromosomes in a parental cell into two daughter cells
What is the special name for the 23rd pair of
chromosomes in humans?
sex chromosomes
Where does the process of meiosis occur
in organisms?
germ cells/sex cells/gametes
How does meiosis I differ from meiosis II?
- In meiosis I, homologous chromosomes separate,
while in meiosis II, sister chromatids separate. - Meiosis II produces 4 haploid daughter cells,
Meiosis I produces 2 diploid daughter cells. - Genetic recombination (crossing over) only occurs
in meiosis I
What is a tetrad composed of?
4 chromatids
What happens during anaphase l?
-homologous chromosomes separate from the tetrad
and migrate to opposite poles of the spindle
-sister chromatids remain attached at their
centromeres
What happens during metaphase ll?
the spindle, attached to the centromeres, moves the sister chromatids so that they line up in the middle of the cell
What happens during prophase ll?
in each haploid daughter cell, a spindle
forms and attaches to the centromeres of the sister chromatids
What happens during prophase l?
-begins with two complete sets of duplicated
chromosomes in the form of sister chromatids
-each duplicated chromosome pairs with its
corresponding homologous chromosome, forming a
tetrad
-the homologous chromosomes then exchange
portions of DNA.
What happens during metaphase l?
tetrads move to the middle of the cell and line up
What happens during telophase l?
-the nuclear membrane re-forms around each cluster
of chromosomes
-chromosomes of each daughter cell are present in
duplicate (as sister chromatids)
-although, each cell is considered HAPLOID
*the cells must go through a second division in
order to have the CORRECT number of chromosomes
What happens during prophase ll?
in each haploid daughter cell, a spindle
forms and attaches to the centromeres of the sister chromatids
What happens during anaphase ll?
-sister chromatids separate and move to opposite
poles of the cell
-once separated, they are considered INDIVIDUAL
chromosomes
What happens during telophase ll?
-chromosomes are at the poles
-separate nuclei begin to form around each group of
chromosomes
What is the exchange of DNA segments called in prophase l?
genetic recombination
What happens during cytokinesis in Meiosis?
-cytokinesis splits the cells one more time
-the process of meiosis is complete
-4 HAPLOID daughter cells is the final result
Name two factors that introduce genetic
variation during the process of meiosis.
crossing-over and independent assortment.
Crossing over:
-Prophase I: homologous chromosomes line up their
chromatids and “cross-over”(GR), or exchange
corresponding segments of DNA with each other
-This produces genetic variation by allowing more
combinations of genes to be produced.
Independent Assortment:
-Anaphase I, homologues separate and move to
opposite sides of the cell.
-Resulting cells have one chromosome from each pair
of homologous chromosomes
-However, WHICH chromosome that each cell gets is
completely random
Cell cycle definition
sequence of events from the production of a eukaryotic cell to the time the cell itself reproduces
Mitotic phase definition
stage of the cell cycle when a cell is actively dividing
Chromosome
condensed threads of genetic material formed from chromatin as a cell prepares to divide
Binary Fission
occurs in prokaryotes, produces two daughter cells genetically identical to the parent cell
Describe one similarity between mitosis and meiosis II. Describe one difference.
-both mitosis and meiosis II are forms of cell division
-cells at the beginning of meiosis II are haploid
Describe the structure of a tetrad. when do tetrads form?
group of four chromatids formed during prophase I of meiosis by the two sister chromatids in each of the two homologous chromosomes
Explain how having a haploid number of chromosomes contributes to the function of gametes in a life cycle.
-having the haploid number of chromosomes allows
the zygote to have the correct number
-if gametes weren’t haploid, every generation of
organisms would have TWICE as many
chromosomes as their parents.
Describe the most obvious way the karyotypes of a sister and brother look different
the sister will have sex chromosomes XX and the brother will have sex chromosomes XY
Explain how cancer tumours spread
cancer tumours spread through the blood stream or the lymphatic system
Identify the two major events that occur during the mitotic phase of the cell cycle
mitosis and cytokinesis
Give three examples of organisms that reproduce asexually
worms, snails, amoebas
Zygote
diploid cell formed when the nucleus of a haploid sperm cell fuses with the nucleus of a haploid egg cell
Fertilization
the fusion of the nucleus of a haploid sperm cell and the nucleus of a haploid egg cell, forming a diploid zygote
Gamete
egg or sperm sex cell that contains a single set of chromosomes, one from each homologous pair
Sex chromosome
one of two chromosomes of the 23rd pair of human chromosomes, which determine an individual’s gender
Karyotype
display of a person’s 46 chromosomes
Cancer
disease caused by severe disruption of the mechanisms that normally control the cell cycle
Malignant tumour
mass of abnormal cells resulting from uncontrolled cancer cell division
Cell plate
disk containing cell wall material that develops in plant cells during cytokinesis, eventually dividing the cell into two daughter cells
Centrosome
-comprises two microtubule rings known as centrioles -main function is to organize the microtubules and
provide a structure to the cell
-pulls the chromatids apart during cell division
STRUCTURE OF DNA
What are the complimentary bonds
A&T
G&C
CELL DIVISION
Explain Mitosis
-a form of a sexual reproduction which is used for:
growth, replacement, and repair
-homologous chromosomes do not pair in mitosis
-daughter cells are identical to the parent cell
CELL DIVISION
Explain Meiosis
-used for sexual reproduction
-process occurs in ovaries and testicles
-makes the gametes (egg and sperm)
-homologous chromosomes pair
-daughter cells have variation (you want it to be
different for survival purposes)
OTHER EVENTS DURING MEIOSIS
crossing over
-sometimes, genes on the paternal chromosomes
SWITCH with genes on the maternal chromosome
-this results in more genetic variation
Explain how genetic recombination occurs
between homologous chromosomes
-when recombination occurs during meiosis, the cell’s
homologous chromosomes line up extremely close to
one another
-then, the DNA strand within each chromosome breaks
in the exact same location, leaving two free ends
-each end then crosses over into the other
chromosome and forms a connection called a
chiasmata.
What is the consequence to a human gamete
if there is no crossing over in meiosis I?
-each chromosome would be either maternal or
paternal, greatly REDUCING the number of possible
genetic combinations
-would greatly reduce the amount of genetic variation
between related individuals and within a species
How does the process of crossing over during
meiosis in an individual organism recombine the
genetic material of the organism’s two parents?
-during meiosis, homologous chromosomes (1 from
each parent) pair along their lengths
-the chromosomes cross over at points called
chiasmata
-At each chiasmata, the chromosomes break and
rejoin, TRADING some of their genes.
Each type of eukaryotic organism has a
characteristic number of chromosomes. Human
somatic cells generally have 46 chromosomes
in their nuclei, while fruit flies generally have
8 chromosomes. If there was only one round
of cell division in meiosis, how might this
affect the chromosome numbers in offspring?
Explain.
-cells would have the incorrect number of chromosomes because they wouldn’t be haploid
Human nerve cells rarely undergo mitosis.
On the basis of this information, why do you
think complete recovery from a nervous-system
injury is rare?
-mitosis is used for growth, repair and reproduction
-if there’s no mitosis, nerve cell aren’t able to
completely repair themselves
If an organism generally has 8 chromosomes in
its somatic cells, how many chromosomes will
its gametes contain?
somatic cells- diploid (2n)
gametes- haploid (n)
–> 4 gametes
During meiosis only chromosomes, not
individual genes, assort randomly. Why?
-individual genes are located on the chromosomes, and when a chromosome moves so do the associated genes on that chromosome
-for genes to all assort independently, they would all have to be completely separate and not on chromosomes.
Explain why it is so important to stay away
from substances that may alter or damage the
DNA in your cells.
-changes in genes can alter a protein’s function in the body, potentially causing health problems
-scientists have determined that changes in regions of DNA that do not contain genes (noncoding DNA) can also lead to disease
Suggest the role of sexual reproduction
in producing genetically varied offspring
-sexual reproduction has the potential to produce tremendous genetic variation in offspring
-this variation is due to independent assortment and crossing-over during meiosis, and random union of gametes during fertilization
Timing and regulation of cell division are CRITICAL for ____________
normal cell growth and development
If incorrect timing/regulation cells will ____________
form a tumour
Malignant tumours
cancer causing
what is cancer caused by
Cancer is caused by a severe disruption in the mechanisms that regulate cell division
Paramecium can reproduce via …
Binary Fission (Asexual Reproduction)
asexual reproduction
Offspring will inherit ALL their genetic material from ONE parent
somatic cells
cells of the body
prophase
Sister chromatids become visible as chromatin shorten and condense
Centrioles separate and move to opposite ends of the cell (in animal cells)
Sister chromatids attach to spindle fibres
Nucleolus and nuclear membrane breaks down
metaphase
Sister chromatids fully attached to spindle fibres
Spindle fibres line chromatids up along the Middle of the cell
in metaphase, cells are lined up along…
equatorial plate
anaphase
Sister chromatids separate from their partners to become individual chromosomes
Spindle fibres pull chromosomes to opposite ends of the cell
telophase
Chromosomes begin to uncoil to take on the form of chromatin
Spindle fibres disappear
Nuclear membrane re-forms around each set of daughter chromosomes
Cytokinesis completes cell division by dividing the cytoplasm into two daughter cells, each with it’s own nucleus
Occurs at the same time as telophase
sexual reproduction
two parents provide genetic material to produce offspring
Each offspring inherits a _________ of traits from their parents
unique combination
Meiosis produces 4 cells, each containing ____ the number of chromosomes as the parent cell
half
In animals, Meiosis occurs in the _____ organs;
sex
Karyotype
a display/map of all chromosomes in a cell
Homologous Chromosomes
two chromosomes of each matching pair
in homologous chromosomes, each member of the pair carries the same series of genes controlling the ______
same inherited trait
Most human cells are ______
diploid
In humans the diploid number is
46, (2n = 46)
sex cells (egg and sperm) also called gametes produced via
Meiosis
in humans the haploid number is
23, (n = 23)
Fusion of haploid sperm and haploid egg is known as
fertilization
zygote is
diploid
what would happen if the gametes were diploid?
the resulting zygote would have 92 chromosomes (too many)
Meiosis enables the zygote to have the ___________
correct # of chromosomes
One set of chromosomes “sex chromosomes” (pair #23) determines
one’s sex
which pairs of chromosomes are autosomes
Chromosome pairs #1-22 (autosomes)
By the end of Meiosis II, the original diploid cell has become _________ cells
4 haploid sex cells
prophase 1
Two complete sets of duplicated chromosomes in the form of sister chromatids
Each duplicated chromosome pairs with its corresponding homologous chromosome, forming a tetrad
Exchange portions of DNA … genetic recombination
metaphase 1
Tetrads move the middle of the cell and line up
anaphase 1
Homologous chromosomes separate from the tetrad and move to opposite ends of the cell (via spindle fibres)
Sister chromatids remain attached at their centromeres
telophase 1
Nuclear membrane re-forms
In humans, 46 chromosomes
Must go through one more round of division to get haploid sex cells
prophase ll
NO replication of DNA
Spindle fibres attach to centromeres of sister chromatids
metaphase ll
Sister chromatids lined up in the middle of the cell
anaphase ll
Sister chromatids separate and move to the opposite ends of the cell (via spindle fibres)
telophase ll
Nuclei begin to re-form around the 4 haploid daughter cells
Cytokinesis will split the cells into 4 unique daughter cells
meiosis new gene combinations
Offspring are genetically different from parents AND from each other
Each parent contributes a unique combination of genes to an offspring
The way in which chromosomes assort (distribute) and how they line up and separate occurs by chance
crossing over
Occurs during Prophase I
Each gene is precisely lined up with the corresponding gene on the adjacent pair of sister chromatids
The close association is known as a synapsis
At regions called chiasmata, chromatids from different pairs are attached and segments of the chromatids are exchanged
Without this process, every chromosome produced by meiosis would just be maternal or just be paternal
At regions called _________, chromatids from different pairs are attached and segments of the chromatids are exchanged
chiasmata
