A review of basic genetics
Meiosis
Mitosis
Meiosis
Meiosis in female
Duplicates & forms 2 chromatids joined at centromere
Line up at centre of cell & pairing or synapsis takes place
Crossing over or recombination of chromatids –
Chiasmata formation
Breaks at crossing over site and exchange segments
Meiosis in female
Centromere pulled to opposite poles – Disjunction
Cell divides into 2 cells
Only one cell function normally, other cell degenerate to
1st polar body
Functional chromatid move apart and divides into 2 cells
Meiosis in female
Again one cell degenerates to 2nd polar body and only
one cell remain as functional gamete
Homogametic sex
Meiosis in male
Similar to female meiosis with 2 distinct differences
Synapsis or pairing occurs in small homologous
region of one arm (called pseudoautosomal region).
No chiasmata formation or crossing over of
chromatids
No polar bodies formed – instead four functional
gametes formed at the end of meiosis
Heterogametic sex
Chance and variation
Male gametes
½X
Female gametes all X ½ XX
½Y
½XY
Mitosis
Mitosis
Chromosome (X and Y) duplicates and forms 2
chromatids joined at centromere
Moves to centre of cell but does not synapse
Centromere splits and chromatids separates
(disjunction)
Chromatids pulled to opposite end or poles (disjunction)
Mitosis
Constriction takes place at centre of cell
Divides into two cells
Two daughter cells, each identical to parent cell formed
(X and Y chromosomes)
Summary
Meiosis in female results into only one functional
gametes while male gives four gametes
Mitosis results into two daughter cells identical to parent
cell
In both meiosis and mitosis chromosomes duplicates
Why such duplication happens will be dealt in next now