Mitosis and meiosis

Question 1

Where in the cell is DNA found?

Answer 1

Nucleus and mitochondria

Question 2

Describe the structure of DNA

Answer 2

Double helix
Complementary base pairs(A double bond T, G triple bond C)
Coils around nucleosomes then into supercoils then into chromosomes

Question 3

How many chromosomes in the human genome?

Answer 3

46(22 pairs and sex chromosomes)

Question 4

Describe the structure of the chromosome

Answer 4

long arm(q) and short arm(p), separated by the centromere
Contain G banding

Question 5

What is mitosis for?

Answer 5

Growth and replacing dead cells

Question 6

What does mitosis produce?

Answer 6

2 daughter cells genetically identical to parent cell

Question 7

What are the 4 stages of the cell cycle?

Answer 7

G1 growth phase, Synthesis phase, G2 growth phase, mitosis

Question 8

What happens in the S phase?

Answer 8

DNA replication

Centrosome replication

Question 9

What are the steps of mitosis?

Answer 9

Prophase
Prometaphase
Metaphase
Anaphase
Telophase

Question 10

What happens during prophase

Answer 10

Chromatin condenses into chromosomes

Centromeres nucleate microtubules and move to opposite poles of the nucles

Question 11

What happens during prometaphase?

Answer 11

Nuclear membrane breaks down
Microtubules invade nuclear space
Chromatids attach to microtubules

Question 12

What happens during metaphase?

Answer 12

Chromosome line up along equatorial plane

Question 13

What happens during anaphase?

Answer 13

Sister chromatids separate and are pushed to opposite poles of the cell

Question 14

What happens during telophase?

Answer 14

Nuclear membranes reform
Chromosomes unfold into chromatin
Cytokinesis begins

Question 15

What is the clinical relevance of mitosis?

Answer 15

• Detecting chromosomal abnormalities
• Categorising tumours as benign or malignant
• Grading malignant tumours

Question 16

How is meiosis different to mitosis?

Answer 16

Only in gametes
Recombination of genetic material generates diversity
2 cell divisions
4 haploid daughter cells

Question 17

When in meiosis does cross over occur?

Answer 17

Prophase 1

Question 18

When do sperm start being produced?

Answer 18

Meiotic divisions start at puberty

Question 19

How are sperm produced?

Answer 19

Primordial germ cells=lots of mitoses=spermatogonia
Cytoplasm divides evenly
After meiosis 2 4 equal gametes are produced

Question 20

How long does sperm production take?

Answer 20

60-65 days

Question 21

How many sperm are produced per ejaculate?

Answer 21

100-200 million

Question 22

Describe the process of egg production

Answer 22

Primordial germ cell=30 mitoses=oogonia
Oognonia enter prophase of meiosis 1 by 8th month of inrauterine life
Process suspended until cell enter ovulation 10-50 years later
Cytoplasm divides unequally-1 egg and 3 polar bodies
Meiosis 1 is completed at ovulation
Meiosis 2 only completed if fertilisation occurs

Question 23

What is non-disjunciton?

Answer 23

Failure of chromosome pairs to separate in meiosis 1 or sister chromatids to separate properly in meiosis 2

Question 24

What causes Down’s syndrome

Answer 24

Regular trisomy 21

Non-disjunction in 21st chromosome-extra chromosome present

Question 25

What is gonadal mosaicism?

Answer 25

One cell line is normal the other is mutated

Question 26

When does gonadal mosaicism occur?

Answer 26

When precursor germline cells to ova or spermatozoa are a mixture of 2 or more genetically different cell lines

Question 27

How does paternal age affect incidence of gonadal mosaicism?

Answer 27

Incidence increases with advancing paternal age

Question 28

How does gonadal mosaicism present in patients?

Answer 28

Parent is healthy but fetus may have a genetic disease

Question 29

Which inheritance patterns can gonadal mosaicism be observed with?

Answer 29

Any inheritance pattern but most commonly autosomal dominant and x-linked

Question 30

Which genetic conditions can arise from gonadal mosaicism?

Answer 30

OI and Duchenne muscular dystrophy