2.3 - Meiosis and Linkage

Question 1

Why is chromosome segregation required?

Answer 1

gametes required to create another living being

Question 2

what does meiosis involve? (2)

Answer 2

1. 1 round DNA replication
2. 2 rounds chromosome segregation

Question 3

What are the 3 stages of meiosis? (3)

Answer 3

1. Interphase
2. Meiosis (metaphase) 1
3. Meiosis (metaphase) 2

Question 4

interphase

Answer 4

chromosomes replicated (homologous pair replicated chromosomes)

Question 5

Meiosis (metaphase) 1

Answer 5

first cell division, homologous pair of replicated chromosomes separate

Question 6

meiosis (metaphase) 2

Answer 6

2nd cell division, sister chromatids separate (produces 4 haploid daughter cells)

Question 7

Independent assortment

Answer 7

homologous chromosomes randomly line up at metaphase plate, orientation of chromosome pairs leads to different combinations of maternal and paternal chromosomes in the resulting gametes

Question 8

how does chromosome separation differ in meiosis compared to mitosis? (2)

Answer 8

1. mitosis - chromosomes attach to spindle fibres, sister chromatids not pulled apart
2. meiosis - homologous chromosomes pulled apart, sister chromatids pulled apart in meiosis 2

Question 9

what is required for meiosis 1? (4)

Answer 9

1. pairing of homologous chromosomes
2. synapsis
3. crossing-over
4. mono-orientation of kinetochore

Question 10

synapsis (2)

Answer 10

1. well orchestrated structure made up of highly conserved and complex proteins
2. allows homologous chromosomes to be together enabling rest of meiosis to occur

Question 11

crossing over

Answer 11

promotes segregation of homologs at meiosis 1

Question 12

holds sister chromatids together

Answer 12

cohesin

Question 13

holds homologous chromosomes together

Answer 13

synapsis

Question 14

Active seperase (3)

Answer 14

1. cohesin needs to be removed to begin allowing sister chromatids to separate
2. active separase removes Rec8 in chromatid arms (cohesin)
3. cohesin still needed around central parts (centromere and kinetochore)

Question 15

Crossover recombination

Answer 15

1. crossing over of different alleles on homologous chromosomes
2. results in novel combinations of alleles in gametes (recombinant chromatids)

Question 16

Importance of crossover recombination

Answer 16

very important for variation of our species

Question 17

Linkage

Answer 17

2 genes on the same chromosome

Question 18

what breaks linkage?

Answer 18

crossovers

Question 19

what does linkage distort?

Answer 19

mendelian ratios

Question 20

what is the parental genotype ratio when theres no crossing over?

Answer 20

1:1

Question 21

what is suggested when phenotypes vary from expected values?

Answer 21

linkage and recombination

Question 22

recombinant frequency

Answer 22

determines how closely linked 2 genes are

Question 23

how to calculate recombinant frequency (4)

Answer 23

1. add up recombinant individuals
2. divide by total phenotypes
3. x100 to get %
4. convert to CentiMorgans (unit of how close recombinant genes are)

Question 24

what does it mean if recombinant frequency is 50% or higher?

Answer 24

genes are on different chromosomes

Question 25

when is recombination more likely to occur?

Answer 25

when genes are further apart on same chromosome

Question 26

what happens when there are 2 crossover events?

Answer 26

parental genotype maintained despite recombination