CBG13

Question 1

What is a meiocyte?

Answer 1

cell thats undergoing meiois

Question 2

what is the difference in production of gametes in spermatogenesis and oogenesis?

Answer 2

• sam principle meiosis

oogenesis - produces 4 polar bodies and 1 egg cell

spermatogenesis - produces 4 sperm

Question 3

What do 2 sister chromatids make?

Answer 3

a dyad

Question 5

What do two homologous chromsomes paired up make?

Answer 5

a bivalent

Question 6

What are two sister chromatids paired in bivalents known as?

Answer 6

tetrad

Question 7

What is the complement?

Answer 7

whole set of chromsomes

Question 8

What is a metacentric?

• acrocentric

Answer 8

centromere in middle

acrocentric - higher or lower centromere

Question 9

In order what are the 5 stages of prophase 1?

Answer 9

leptotene

zygotene

pachytene

diplotene

diakinesis

Question 10

What happens in leptotene

Answer 10

• chromatic condense and coil, chromsomes become visible
• homology search for paired chromosome

Question 11

what happens in zygotene?

Answer 11

• shortening and thickening and inital rough pairing
• synaptomenal complex forms
• paired homologous bivalents.

Question 12

what happens in pachytene?

Answer 12

1. more condensing
2. chromatids may be visible
3. SC - pairing stronger
4. crossing over between non sister chromatids
5. chiasmata form at cross over

Question 13

What happens in diplotene?

Answer 13

1. SC starts to break down
2. repulsion of homologous chromsomes extends along lengths except at chiasmata
3. chromatids evident - mid - late

Question 14

What happens in diakenesis?

Answer 14

atleast one chiasmata holds the tetrad together

spindle formation

nucelus and nucelar envelope break down

2 centromeres of tetraf attach to spindles.

Question 15

What is the synaptomenal complex?

Answer 15

binds to tetrad

protein

mediates chromsome pairing, synapsis and recombination

no SC in make drosophilia

* therefore gene mapping uses F1 female heterozygotes as relies on recombination

Question 16

what happens in early anaphase 1?

Answer 16

contraction of spindle fibres drags apart the homologous chromosomes

Question 17

What does random alignment of bivalents in dihybrid F1 lead to?

Answer 17

recombinant gametic genotypes for genes on different chromsomes

Question 18

What are the spindle plains in first and second division?

Answer 18

first divison is on the opposite plain of second

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Question 19

What is the recombination frequency?

Answer 19

%RF= no. of recombinants/total no. x100

for genes on difference chromosomes RF=2/4*100 =50%

no preferential arrangement of alleles

Question 20

What can test crosses reveal?

Answer 20

1. incomplete linkage RF= 0-50%

ussuaully <50

should end up with more parentals then recombinants

if so far apart can get frequent crossover as many recombinants as parents

2. complete linkage

f1 dihybrid X recessive homozygote

-AaBb X aabb

if ratio = 1:1:1:1 RF=50%

complete linkage shown by F2 ratio with only parental gametes produced RF=0%

Question 21

What is syntenic?

non syntenic?

Answer 21

syntenic - genetic info on same chromosome

non syntenic = different loci

Question 22

What were morgans insights concerning linkage?

Answer 22

Morgans first insight

linked genes segregate together unless crossing over and recombination occur

Morgans second insight

genes linearly arranged on chromosome- % RF depends on distance between them

Question 23

What was morgans experiment and what did he gage from it?

Answer 23

Morgans incomplete sex linkage

independent assortment would elad to 1:1:1:1

complete linkage 1:1

neither - incomplete low frequency recombinance

%RF= 85+44/sum of all x 100 = 1.44%