Lecture 16

Question 1

When is homologous recombination important?

Answer 1

Meiosis: generating diversty and chromosome segregation
Mitosis: repair DNA damage and stalled replication forks

Question 2

What does crossing over take place between?

Answer 2

Non sister chromatids

Question 3

Recombination

Answer 3

reassortment of genetic material already present

Question 4

Meiotic recombination

Answer 4

aspect of sexual reproduction that can enhance genetic variability

Question 5

Sister chromatids

Answer 5

each of 2 identical copies of a replicated chromosome. Must be linked at the centromere.

Question 6

bivalent

Answer 6

4 chromatids

Question 7

Diad

Answer 7

2 chromatids

Question 8

Monad

Answer 8

one chromatid

Question 9

First stage of prophase one

Answer 9

Leptotene

Question 10

Leptotene

Answer 10

means thread

chromosomes become visible

Question 11

2nd stage of prophase one

Answer 11

Zygotene

Question 12

Zygotene

Answer 12

zygo=pair
Chromosomes pair
Synapsis occurs

Question 13

synapsis

Answer 13

pairing of homologous chromosomes

Question 14

3rd stage of prophase I

Answer 14

Pachytene

Question 15

Pachytene

Answer 15

bivalents appear

Synaptonemal complex

Question 16

Synaptonemal complex

Answer 16

forms between synapsed chromosomes and allows homologous pairing along the entire length
believed to be necessary for recombination to occur

Question 17

4th stage of prophase I

Answer 17

Diplotene

Question 18

Diplotene

Answer 18

Chiasmata form

Question 19

Chiasmata

Answer 19

sites of contact

Question 20

5th stage of prophase I

Answer 20

Diakinesis

Question 21

Terminalization

Answer 21

Chiasmata move out to the termini of chromosomes

Question 22

Axial element

Answer 22

proteinaceous structure around chromsomes that condenses at the start of synapsis

Question 23

Lateral element

Answer 23

structure in the synaptonemal complex that forms when a pair of sister chromatids condense

Question 24

Holiday Model steps

Answer 24

1. Endonuclease nicks strand & denaturation occurs
2. Joint molecule forms (complex strands reassociated and are sealed by ligase)
3. Strands opposite crossover strands are nicked by endonuclease
4. Rotation of the axis (branch migration can occur)
5. New DNA synthesis & gaps filled
6. Seals by ligase
7. Have heteroduplex DNA

Question 25

Basic holliday model steps

Answer 25

1. breakage 2. reunion 3. reciprocal exchange

Question 26

Branch migration

Answer 26

recombinant joint can move along the chromosome

Question 27

Topoisomerases

Answer 27

relieve tension from the twisting of DNA by breaking then remaking bond

Question 28

Type 1 topoisomerase

Answer 28

breaks single strand of DNA

Question 29

Type 2 topisomerase

Answer 29

breaks double strand of DNA

Question 30

Robertsonian fusion

Answer 30

2 acrocentric chromosomes recombine and fuse to metacentric

Question 31

Chromosome fusion

Answer 31

2 NON homologous chromosomes fuse into 1

Question 32

Chromosome fission

Answer 32

A chromosome splits into 2 chromosomes

Question 33

Where are robertsonain changes common?

Answer 33

plant and animal kingdom