Genetic Code: Mitosis and Meiosis

Question 1

What is the structure of DNA?

Answer 1

Double Helix

Genetic material that is bound around histones, becoming nucleosomes, then supercoils into chromosomes.

Question 2

How many chromosomes are there in each cell, in humans?

Answer 2

23 pairs, so 46 chromosomes.

Question 3

Karyotype

Answer 3

The number and appearance of chromosomes in a cell.

Spreads are arranged in size order where the biggest pair is pair 1

Question 4

Statistics within DNA

Answer 4

Each chromosome contains roughly:
10^7 base pairs
around 30,000 genes

Question 5

p and q chromosome

Answer 5

p=short arm
q=long arm
each separated by a centromere

Question 6

Mitosis

Answer 6

Process of cell replication where 2 genetically identical daughter cells are formed (to the parents), for cell growth and replication.

Question 7

Chromatin, chromosomes, chromatid

Answer 7

They are all the same
Chromatin= before cell replication
Chromosomes= During cell replication
Chromatid= After cell replication

Question 8

Interphase: G1

Answer 8

(No visible change is occurring)

• Normal metabolic function
• New organelles formed
• Protein synthesis of the proteins involved in spindle formation

Question 9

Interphase: S Phase (Synthesis)

Answer 9

• DNA replicated, making double the amount of DNA
• Histone protein doubles
• Centrosome replication

Question 10

Interphase: G2

Answer 10

• Mitochondria and centrioles double

- Microtubules are formed

Question 11

Prophase

Answer 11

• Chromatin condenses into chromosomes
• Becomes visible under . microscope
• Centrosomes nucleate microtubules that move to opposite ends of the pole

Question 12

Prometaphase

Answer 12

• The two identical chromosomes join by a centromere
• Microtubules invade the nuclear space
• Chromatids attach to the microtubules
• Nuclear membrane breaks down
• Nucleus i destroyed

Question 13

Metaphase

Answer 13

-The chromosomes line up horizontally across the equatorial plane, forming the metaphase plane

Question 14

Anaphase

Answer 14

-The sister chromatids separate and are pulled to the opposite sides of the cell, centromere first, as the spindle fibres contract.

Question 15

Telophase

Answer 15

• Nuclear membrane reforms
• Chromosomes de-condense back into chromatids
• Cytokinesis begins
• 4n amount of chromosomes, but two nuclei are present

Question 16

Cytokinesis

Answer 16

-Cell divides into two cells, each with a nucleus containing 23 pairs of chromosomes each

Question 17

Down’s Syndrome

Answer 17

Trisomy of chromosome 21

trisomy 21

Question 18

How can you tell if a cell is undergoing mitosis?

Answer 18

• If the nucleus is dark due to the condensed chromosomes

- If the nuclei are not the same size

Question 19

How do you recognise malignant cells?

Answer 19

If there are too many mitotic figures i.e. lots of dark nuclei of different sizes
-The higher the mitotic figure, the worse the cancer

Question 20

What makes meiosis different to mitosis?

Answer 20

• only in gametes
• recombination of genetic material, resulting in genetic diversity
• Two cell divisions
• 4 (each of them containing n numbers f chromosomes) haploid cells formed, which are genetically distinct to each other and the parent cell
• Meiosis is not a cycle

Question 21

What happens in mitosis 1 of meiosis?

Answer 21

• Genetic material is duplicated, creating two 4n chromosomes
• Crossing over of genetic material occurs during prophase 1
• Mitosis 1 occurs and forms two daughter cells each containing 2n amount of chromosomes

Question 22

What happens in mitosis 2 of meiosis?

Answer 22

• Independent segregation

- Creates 4 haploid daughter cells, containing n amount of chromosomes (haploid)

Question 23

How are male gametes developed and matured?

Answer 23

Primordial germ cells–> Lots of mitosis occurs–>Spermatogonia (immature sperm cell)

• Some of this mitosis occurs during the embryonic stage of males’ life, forming primary spermatocytes
• Mitosis really just begins during puberty
• The cytoplasm divides evenly, during meiosis
• Millions of sperm produced continually
• 60-65 days
• 100/200 million sperm per ejaculation

Question 24

How are female gametes developed and matured? (oogenisis)

Answer 24

Primordial germ cells (Undifferentiated)–>30 mitoses–>oogonia

• The oogonia enters prophase 1 of meiosis 1 by the 8th month of intrauterine life.
• Meiosis is suspended
• The cells enter ovulation 10-50 years later
• Meiosis 1 is completed during ovulation:
• Cytoplasm divides unequally, forming 1 egg cell (primary oocytes) and three polar bodies that go on to apoptose.
• Meiosis 2 occurs if the egg cell becomes fertilised.

Question 25

Non-disjunction mutation

What can it cause?

Answer 25

1) The failure of chromosomes to separate during meiosis 1 or the failure of the sister chromatids to separate during meiosis 2.
2) It can cause trisomy 21 (Down’s Syndrome) and also monosomy (e.g. Turner’s syndrome where there is only one X chromosome)

Question 26

What is Gonadal Mosaicism?

How is this incidence increased?

Is the parent affected?

Answer 26

1)occurs when precursor germline cells are a mixture of two or more genetically different cell lines, due to errors in mitosis.
One cell line is normal whereas the other is mutated.

2) Advancing paternal age
3) The parent is unaffected because the germ line cells are only genetically affected. The offspring may have a genetic disease due to it.

Question 27

where are gonadal mosaicism genetic diseases common in?

provide examples of genetic conditions caused by gonadal mosaicism.

Answer 27

Though this can be observed in any inheritance pattern, this can mostly commonly cause an autosomal dominance or X-linked genetic diseases.

Osteogenesis imperfecta and Duchenne muscular dystrophy