LiroxtronIV (LiroxtronIV)-
outline the behaviour of chromosomes during meiosis
P1
chromatin condenses to form cms made up of 2 = SC held tgt @ ctm > HC pair up to form bivalent->synapsis > crossing over occur b/w non-SC of HC > sections of cmt w/ = genes break,rejoin give new combinations of alleles, forms RC
M1
cms arranged along metaphase plate in bivalents > IA of HC, arrangement of cms of each bivalent independent of others
A1
HC pulled to opp poles of cell when SF attached to ctm shorten, contract
T1
HC reach opp poles of cell, uncoil, lengthen, becomes indistinct to form chromatin
P2
chromatin condenses to form cms made up of 2 cmt held tgt @ ctm
M2
cms arranged in single row on metaphase plate > IA of cmt, arrangement of cmt of each cms independent of others
A2
ctm divide, cmt separate @ centromere > each cmt now daughter cms, pulled to opp poles of cell
T2
DC reach opp poles of cell, uncoil, lengthen, becomes indistinct to form chromatin
-
outline the behaviour of nuclear envelope during meiosis
P1, P2
nucleolus disappears, nuclear envelope disintegrates, fragments into nuclear membrane vesicles
T1, T2
nuclear membrane vesicles bind to chromosomes, fuse tgt > nuclear envelope reforms around each set of chromosomes in each daughter cell > nucleolus reforms in each daughter nucleus
-
outline the behaviour of centrioles during meiosis
P1, P2
SF form, kinetochore SF from each pole attach to centromeres > SF on 1 pole attach to 1 homologue, that of opp pole attach to other homologue
A1, A2
SF shorten, contract pulling HC to opp poles of cell > chiasmata dissociate as 2 HC separate independently, move to opp poles of cell
T1, T2
SF disintegrate
-
explain significance of meiotic cell cycle
1. allows maintenance of constant cms number in every gen of species
> reduction of 2n->n in gametes > fertilisation, nuclei of 2 n gametes fuse, produce 2n zygote > if meiosis didnt occur, fusion of gametes result in doubling of cms no.
2. allows genetic variation in genotype, phenotype of offspring
> ensures species constantly evolve for higher chances of survival when env conditions change
-
how meiosis leads to genetic variation?
crossing over
crossing over b/w non-SC of HC in P1 > sections of chromatids w/ same genes break, rejoin to give new combinations of alleles
IA & IS
IA of HC/bivalents in M1, IA of RC in M2 > results in IA of parental chromosomes b/w nuclei of daughter cells producing new combinations of alleles in gametes
-
define chromosomal aberration
change in cms no. OR structural alteration to cms
-
define anueploidy and explain how it occurs
anueploidy; 1 or several cms more/less than 2n no. of cms can occur >
non-disjunction occurs when HC/cmt fail to separate properly during A1/A2 >
fusion of gamete w/ n-2/n-1/n+1/n+2 cms + normal n gamete -> child w/ chromosomal aberration
-
define polyploidy and explain how it occurs
polyploidy; 3x/> 2n no. of cms >
results from non-disjunction, fusion of 2n gamete + normal n gamete giving 3n nucleus
-
what are the types of structural aberrations to chromosomes?
Translocation; section of cms breaks off from cms, attaches to another cms
Duplication; section of cms replicates, set of gene loci repeated
Deletion; cms breaks @ 2 points, middle portion of cms displaced, 2 ends join tgt > shorter cms containing < genes forms
Inversion; cms breaks @ 2 locations, middle portion inverts before rejoining
