Cell Division Flashcards
What is the difference between mitosis and meiosis?
Mitosis produces 2 identical daughter cells, while meiosis produces 4 daughter cells (gametes) with genetic variation
How many chromosomes, chromatids, and DNA molecules are there after S phase and during G2 phase of mitosis?
There are 46 chromosomes, 92 chromatids, and 46 DNA molecules
What are centrosomes?
Centrosomes are structures made of y-tubulin, that migrate to opposite ends of the cell and make it bi-polar - from here, mitotic spindles segregate the chromatids into seperate daughter cells to ensure there are 46 chromosomes per cell
How have taxols proved successful in targeting cancer cells?
Taxols disrupt the growth of the microtubules, meaning that they cannot pull sister chromatids apart and so cannot form 2 viable daughter cells
What is interesting about the number of centrosomes in a cancer cell?
They usually have more than 2
How may a cancer cell propagate in spite of having more than 2 centrosomes?
They cluster the spare centrosomes in other compartments of the cell, which do not interfere with cell division
How have modern therapeutic techniques been able to target the increased number of centromeres in a cancer cell? Why does it not affect normal cells?
Modern drugs may inhibit centrosome clustering, meaning that cancer cells will not be dividing into viable daughter cells and will die - this doesn’t affect normal cells as they have 2 centrosomes, and will continue to divide normally
What are the cell cycle checkpoints? Where do they occur?
The cell cycle check points are points that assess environmental factors, ensuring they are appropriate before beginning the next stage of the cell division cycle - they occur towards the end of G1 & G2
What is the function of cohesin?
Cohesin holds the homologous sister chromatids together, ensuring they do not become seperated before they are moved into their respective daughter cells
How many sub-units comprise cohesin?
4
What is the difference between homozygous and heterozygous?
Homozygous states that the 2 alleles of a gene inherited by an individual are the same, while heterozygous states that the 2 alleles of a gene inherited by an individual are different
What is hemizygous?
There is only one allele of a gene, on the X chromosome (therefore only males express this type of inheritance)
In a heterozygote, how is it determined which allele is expressed?
Now allele is dominant, while the other is recessive
What is co-dominance?
This relates to heterozygotes where neither allele is dominant or recessive, and so both alleles are expressed
What is the risk percentage of 2 carriers of a recessive disease having a child has the disease phenotype?
25%
In a heterozygous recessive disease, how many alleles are required for an individual to exhibit the disease phenotype?
Both alleles (2)
In a heterozygous dominant disease, how many alleles are required for an individual to express the disease phenotype?
Just 1 (the disease) dominant allele
Name 1 disease that is the result of a recessive allele. What is the mutation that occurs?
Cystic fibrosis - a mutation in the CFTR gene - F508 is the most common mutation, which leads to the loss of a phenylalanine at position 508 of the CFTR protein
What can you say about the parents of an individual with an autosomal dominant disease?
At least one of the parents will also express the disease phenotype
Why are X-linked recessive diseases more common in males?
They only need to inherit 1 allele (as they only inherit 1 maternal X chromosome) in order to inherit the disease
Can males with an X-linked recessive disorder pass it on to their sons? Why?
No - they will only pass their Y chromosome to their sons - the sons won’t inherit an X chromosome from their father
What is the chance the a heterozygous female carrier of an X-linked recessive disorder will pass the disorder onto their male offspring? Why?
50% - there is a 50% chance the son will inherit either allele (as they will also inherit their Y chromosome from their father)
How may you be able to infer whether is X-linked or not by a brief look at a pedigree diagram?
An unequal distribution of the disorder between males and females
What does whether a disorder is monogenic or polygenic refer to?
Whether the disorder is directly the result of a singular genetic abnormality or whether multiple genetic abnormalities result in a disorder
How are mitochondrial diseases inherited?
Maternally (through the mother)
In what manner is albinism inherited? Is it monogenic or polygenic?
In a recessive manner - it is apolygenic disorder
What makes some disorders more likely to be the result of polygenic inheritance?
Their proximity (i.e. how close they are) of the genes on a particular chromosome
What are 2 homologous chromatids called?
Sisters
What is the short arm of a chromosome referred as? What is a long arm referred as?
The short arm is called the p arm - the long arm is called the q arm
What repeat sequence is associated with telomeres?
TTAGGG
What are the 4 types of centromere? Describe their position in regards to the centre of the chromosome.
- metacentric - directly in the centre
- submetacentric - just off-centre
- acrocentric - grossly off-centre
- telocentric - at the telomere
What links the p and q arms of a chromosome?
A centromere
List the stages of cell division in chronological order.
- prophase
- prometaphase
- metaphase
- anaphase
- telophase
What is cytokinesis?
Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parent cell into 2 daughter cells
What occurs in prophase of mitosis?
The nuclear membrane dissolves, and the chromosomes condense
What is the kinetochore?
The part of the chromosome (more specifically the part of the centromere) that the microtubules connect to
What occurs at prometaphase of mitosis?
Microtubules connect to the kinetochore
What occurs in metaphase of mitosis?
The 46 chromosomes (92 chromatids) line up at the midline of the cell
What occurs in anaphase of mitosis?
The kinetochore fibres pull the homologous chromatids to opposite parts of the cell
What occurs during telophase of mitosis?
The kinetochore fibres disintegrate and the nuclear membrane(s) reappear
Where are the chromosomes during interphase?
Chromosomes are not condensed during interphase so you cannot see them - they do not exhibit their classic X shape in this phase
What is a variant of the same gene called?
An allele
Everybody has 2 copies of a chromosome - are chromatids on two different chromosome 1 molecules sisters? Do they contain the same genes?
They are not sisters, but will contain the same genes (but will probably contain different alleles of these genes)
Are gametes diploid of haploid?
Haploid
How do chromosomes line up in metaphase I of meiosis?
They line up with their homologous pair
What is crossing over? When in cell division does this occur?
Crossing over is the genetic exchange of material between 2 homologous chromosomes, creating genetic variation - this occurs in prophase I
What is a chiasmata?
The point at which 2 homologous chromosomes exchange genetic material during crossing over in prophase I of meiosis
How many chromatids are lined up next to each other in metaphase I of meiosis? What is this called?
4 chromatids are lined up - this is called a tetrad
At the end of telophase I of meiosis, how many chromosomes are in each daughter cell?
23 (but 46 chromatids are in each daughter cell)
What does the random assortment of chromosomes refer to?
The random order in which paternal and maternal chromosomes line up at the midline in metaphase I
What cell gives rise to mature sperm?
A spermatogonium - this produces a primary spermatocyte, which go on to form primary sperm
What gives rise to an ovum?
An oogonium - this differentiates into a primary oocyte, which mature into an ovum
During which phases of the cell cycle are chromosomes heavily condensed?
Prophase, anaphase, and metaphase
During which phase of the cell cycle are chromosomes replicated?
S phase
What is the nucleolus?
The nucleolus is an unbound area of the nucleus where it is responsible for the creation of ribosomes, containing various rRNAs
When in the cell cycle is the nucleolus normally present?
During interphase
During meiosis I, how do homologous chromosomes find each other at the midline?
Due to the similarity in the regions of the genes they share
How do the sex chromosomes find one another?
Through PAR regions
What is aneuploidy?
An error in cell division, resulting in an abnormal number of chromosomes in the daughter cell after division
Why does aneuploidy of the sex cells have fewer consequences than aneuploidy of other cells?
The sex cells contain less genetic information, meaning that genes necessary for viability are not lost
What is anaphase lag? Why might it occur, and what are its consequences?
Anaphase lag describes a delayed movement during anaphase - this may be because a kinetochore spindle has failed to attach to the kinetochore of the chromatid is tardily drawn to its polar region - this will result in aneuploidy
