Week 1: DNA/ Chromosomes

Question 1

What are the 2 pyrimidines (DNA)

Answer 1

Cytosine, Thymine

Question 2

What are the two purines

Answer 2

Adenine, Guanine

Question 3

What state is DNA in majority of the time?

Answer 3

Chromatin

Question 4

What is the 1st level of DNA packing + name 3 characteristics

Answer 4

Nucleosomes: DNA bound to histone

• Dynamic
• Remains intact in entire cell cycle
• Form looped domains

Question 5

Explain discontinuous variations

Answer 5

Mutants: rare discontinuous variants

• Clearly defined phenotypes e.g. blue v.s brown eyes
• 2 or more = polymorphisms
• Various forms: morphs
• Selectively neutral

Question 6

What is pulled apart during cell devision?

Answer 6

Sister chromatids

Question 7

What occurs in G1?

Answer 7

Cell division

Question 8

What occurs in S phase?

Answer 8

• DNA synthesis

- DNA chromosome: now 2 sister chromatids

Question 9

What are the phases of interphase?

Answer 9

G1, S, G2

Question 10

What are the subphases of mitosis?

Answer 10

1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase/ cytokinesis

Question 11

Explain the G2 phase

Answer 11

• Nucleus well defined
• 2 centrosomes (each with 2 centrioles)
• Microtubules extend

Question 12

Explain prophase

Answer 12

Chromatin condenses

Miotic spindle begins to form

Question 13

Explain prometaphase (5 points)

Answer 13

• NE fragments
• Mitotic spindle invades nuclear area
• Chromosomes condense more
• Spindle microtubules extend: capture chromosome at kinetochore
• Non kinetochore interact w/ opposite pole

Question 14

Explain metaphase (2 points)

Answer 14

• Chromosomes align at metaphase plate

- Kinetochores of sister chromatids attached to microtubules

Question 15

Explain anaphase

Answer 15

• Sister chromosomes split
• move towards opposite poles
• Kinetochores shorten, non kinetochores lengthen

Question 16

Explain telophase

Answer 16

• Daughter nuclei + envelope forms

- NKMT extend more

Question 17

Explain cytokinesis

Answer 17

• Division of cell into two

- Cleavage furrow at metaphase plate

Question 18

Explain the 2 types of G0 phase

Answer 18

Reversible: quiescent
- Can re-enter cycle
Irreversible: senescent
- DNA damage/ differentiated cells

Question 19

Where do the checkpoints of the cell cycle occur?

Answer 19

G1, G2, M phase

Question 20

Define Karyotype

Answer 20

picture of a persons chromosomes

Question 21

Define loci

Answer 21

Found on homologus chromosomes same gene in same location

Question 22

Define tetrad chiasmata

Answer 22

when homologous chromosomes pair up + synapse usually in meiosis 1

Question 23

Name 3 processes that cause genetic variation

Answer 23

Independent assortment
Crossing over/ chiasmata
Random fertilisation

Question 24

Explain crossing over

Answer 24

• Occurs in prophase 1
• Pairing is precise
• Crossing over is when homologous portions of 2 non-sister chromatids trade places
• 2/3x per pair