CBG13 Flashcards
What is a meiocyte?
cell thats undergoing meiois
what is the difference in production of gametes in spermatogenesis and oogenesis?
- sam principle meiosis
oogenesis - produces 4 polar bodies and 1 egg cell
spermatogenesis - produces 4 sperm
What do 2 sister chromatids make?
a dyad
What do two homologous chromsomes paired up make?
a bivalent
What are two sister chromatids paired in bivalents known as?
tetrad
What is the complement?
whole set of chromsomes
What is a metacentric?
- acrocentric
centromere in middle
acrocentric - higher or lower centromere
In order what are the 5 stages of prophase 1?
leptotene
zygotene
pachytene
diplotene
diakinesis
What happens in leptotene
- chromatic condense and coil, chromsomes become visible
- homology search for paired chromosome
what happens in zygotene?
- shortening and thickening and inital rough pairing
- synaptomenal complex forms
- paired homologous bivalents.
what happens in pachytene?
- more condensing
- chromatids may be visible
- SC - pairing stronger
- crossing over between non sister chromatids
- chiasmata form at cross over
What happens in diplotene?
- SC starts to break down
- repulsion of homologous chromsomes extends along lengths except at chiasmata
- chromatids evident - mid - late
What happens in diakenesis?
atleast one chiasmata holds the tetrad together
spindle formation
nucelus and nucelar envelope break down
2 centromeres of tetraf attach to spindles.
What is the synaptomenal complex?
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
what happens in early anaphase 1?
contraction of spindle fibres drags apart the homologous chromosomes
What does random alignment of bivalents in dihybrid F1 lead to?
recombinant gametic genotypes for genes on different chromsomes
What are the spindle plains in first and second division?
first divison is on the opposite plain of second
— |
What is the recombination frequency?
%RF= no. of recombinants/total no. x100
for genes on difference chromosomes RF=2/4*100 =50%
no preferential arrangement of alleles
What can test crosses reveal?
- 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
- 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%
What is syntenic?
non syntenic?
syntenic - genetic info on same chromosome
non syntenic = different loci
What were morgans insights concerning linkage?
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
What was morgans experiment and what did he gage from it?
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%
