Cell Division

Question 1

What is the difference between mitosis and meiosis?

Answer 1

Mitosis produces 2 identical daughter cells, while meiosis produces 4 daughter cells (gametes) with genetic variation

Question 2

How many chromosomes, chromatids, and DNA molecules are there after S phase and during G2 phase of mitosis?

Answer 2

There are 46 chromosomes, 92 chromatids, and 46 DNA molecules

Question 3

What are centrosomes?

Answer 3

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

Question 4

How have taxols proved successful in targeting cancer cells?

Answer 4

Taxols disrupt the growth of the microtubules, meaning that they cannot pull sister chromatids apart and so cannot form 2 viable daughter cells

Question 5

What is interesting about the number of centrosomes in a cancer cell?

Answer 5

They usually have more than 2

Question 6

How may a cancer cell propagate in spite of having more than 2 centrosomes?

Answer 6

They cluster the spare centrosomes in other compartments of the cell, which do not interfere with cell division

Question 7

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?

Answer 7

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

Question 8

What are the cell cycle checkpoints? Where do they occur?

Answer 8

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

Question 9

What is the function of cohesin?

Answer 9

Cohesin holds the homologous sister chromatids together, ensuring they do not become seperated before they are moved into their respective daughter cells

Question 10

How many sub-units comprise cohesin?

Answer 10

4

Question 11

What is the difference between homozygous and heterozygous?

Answer 11

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

Question 12

What is hemizygous?

Answer 12

There is only one allele of a gene, on the X chromosome (therefore only males express this type of inheritance)

Question 13

In a heterozygote, how is it determined which allele is expressed?

Answer 13

Now allele is dominant, while the other is recessive

Question 14

What is co-dominance?

Answer 14

This relates to heterozygotes where neither allele is dominant or recessive, and so both alleles are expressed

Question 15

What is the risk percentage of 2 carriers of a recessive disease having a child has the disease phenotype?

Answer 15

25%

Question 16

In a heterozygous recessive disease, how many alleles are required for an individual to exhibit the disease phenotype?

Answer 16

Both alleles (2)

Question 17

In a heterozygous dominant disease, how many alleles are required for an individual to express the disease phenotype?

Answer 17

Just 1 (the disease) dominant allele

Question 18

Name 1 disease that is the result of a recessive allele. What is the mutation that occurs?

Answer 18

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

Question 19

What can you say about the parents of an individual with an autosomal dominant disease?

Answer 19

At least one of the parents will also express the disease phenotype

Question 20

Why are X-linked recessive diseases more common in males?

Answer 20

They only need to inherit 1 allele (as they only inherit 1 maternal X chromosome) in order to inherit the disease

Question 21

Can males with an X-linked recessive disorder pass it on to their sons? Why?

Answer 21

No - they will only pass their Y chromosome to their sons - the sons won’t inherit an X chromosome from their father

Question 22

What is the chance the a heterozygous female carrier of an X-linked recessive disorder will pass the disorder onto their male offspring? Why?

Answer 22

50% - there is a 50% chance the son will inherit either allele (as they will also inherit their Y chromosome from their father)

Question 23

How may you be able to infer whether is X-linked or not by a brief look at a pedigree diagram?

Answer 23

An unequal distribution of the disorder between males and females

Question 24

What does whether a disorder is monogenic or polygenic refer to?

Answer 24

Whether the disorder is directly the result of a singular genetic abnormality or whether multiple genetic abnormalities result in a disorder

Question 25

How are mitochondrial diseases inherited?

Answer 25

Maternally (through the mother)

Question 26

In what manner is albinism inherited? Is it monogenic or polygenic?

Answer 26

In a recessive manner - it is apolygenic disorder

Question 27

What makes some disorders more likely to be the result of polygenic inheritance?

Answer 27

Their proximity (i.e. how close they are) of the genes on a particular chromosome

Question 28

What are 2 homologous chromatids called?

Answer 28

Sisters

Question 29

What is the short arm of a chromosome referred as? What is a long arm referred as?

Answer 29

The short arm is called the p arm - the long arm is called the q arm

Question 30

What repeat sequence is associated with telomeres?

Answer 30

TTAGGG

Question 31

What are the 4 types of centromere? Describe their position in regards to the centre of the chromosome.

Answer 31

- metacentric - directly in the centre - submetacentric - just off-centre - acrocentric - grossly off-centre - telocentric - at the telomere

Question 32

What links the p and q arms of a chromosome?

Answer 32

A centromere

Question 33

List the stages of cell division in chronological order.

Answer 33

- prophase - prometaphase - metaphase - anaphase - telophase

Question 34

What is cytokinesis?

Answer 34

Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parent cell into 2 daughter cells

Question 35

What occurs in prophase of mitosis?

Answer 35

The nuclear membrane dissolves, and the chromosomes condense

Question 36

What is the kinetochore?

Answer 36

The part of the chromosome (more specifically the part of the centromere) that the microtubules connect to

Question 37

What occurs at prometaphase of mitosis?

Answer 37

Microtubules connect to the kinetochore

Question 38

What occurs in metaphase of mitosis?

Answer 38

The 46 chromosomes (92 chromatids) line up at the midline of the cell

Question 39

What occurs in anaphase of mitosis?

Answer 39

The kinetochore fibres pull the homologous chromatids to opposite parts of the cell

Question 40

What occurs during telophase of mitosis?

Answer 40

The kinetochore fibres disintegrate and the nuclear membrane(s) reappear

Question 41

Where are the chromosomes during interphase?

Answer 41

Chromosomes are not condensed during interphase so you cannot see them - they do not exhibit their classic X shape in this phase

Question 42

What is a variant of the same gene called?

Answer 42

An allele

Question 43

Everybody has 2 copies of a chromosome - are chromatids on two different chromosome 1 molecules sisters? Do they contain the same genes?

Answer 43

They are not sisters, but will contain the same genes (but will probably contain different alleles of these genes)

Question 44

Are gametes diploid of haploid?

Answer 44

Haploid

Question 45

How do chromosomes line up in metaphase I of meiosis?

Answer 45

They line up with their homologous pair

Question 46

What is crossing over? When in cell division does this occur?

Answer 46

Crossing over is the genetic exchange of material between 2 homologous chromosomes, creating genetic variation - this occurs in prophase I

Question 47

What is a chiasmata?

Answer 47

The point at which 2 homologous chromosomes exchange genetic material during crossing over in prophase I of meiosis

Question 48

How many chromatids are lined up next to each other in metaphase I of meiosis? What is this called?

Answer 48

4 chromatids are lined up - this is called a tetrad

Question 49

At the end of telophase I of meiosis, how many chromosomes are in each daughter cell?

Answer 49

23 (but 46 chromatids are in each daughter cell)

Question 50

What does the random assortment of chromosomes refer to?

Answer 50

The random order in which paternal and maternal chromosomes line up at the midline in metaphase I

Question 51

What cell gives rise to mature sperm?

Answer 51

A spermatogonium - this produces a primary spermatocyte, which go on to form primary sperm

Question 52

What gives rise to an ovum?

Answer 52

An oogonium - this differentiates into a primary oocyte, which mature into an ovum

Question 53

During which phases of the cell cycle are chromosomes heavily condensed?

Answer 53

Prophase, anaphase, and metaphase

Question 54

During which phase of the cell cycle are chromosomes replicated?

Answer 54

S phase

Question 55

What is the nucleolus?

Answer 55

The nucleolus is an unbound area of the nucleus where it is responsible for the creation of ribosomes, containing various rRNAs

Question 56

When in the cell cycle is the nucleolus normally present?

Answer 56

During interphase

Question 57

During meiosis I, how do homologous chromosomes find each other at the midline?

Answer 57

Due to the similarity in the regions of the genes they share

Question 58

How do the sex chromosomes find one another?

Answer 58

Through PAR regions

Question 59

What is aneuploidy?

Answer 59

An error in cell division, resulting in an abnormal number of chromosomes in the daughter cell after division

Question 60

Why does aneuploidy of the sex cells have fewer consequences than aneuploidy of other cells?

Answer 60

The sex cells contain less genetic information, meaning that genes necessary for viability are not lost

Question 61

What is anaphase lag? Why might it occur, and what are its consequences?

Answer 61

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