Meosis and non disjunction

prophase 1

Only time when crossing ver of allies happens Chororsomes from tretrads. 4 Tatrads and 4 chorotids.

Prophase 2

chomos condenced spindle fiders form

Metaphase !

Chromosomes line up in homolgos pairs in the middle.so that chromosomes of maternal and paternal origin will end up at opposing poles

Metaphase 2

Sister chromatids align at the equatorial plate

In a single row now because they’re haploid

ANAPHASE 1

Spindle fibres shorten, pulling homologous chromosomes apart Centromeres don’t break. Sister chromatids remain together, so that each new pole has a one from each pair of chromosomes

Anaphase 2

The centromeres divides (breaks)

Sister chromatids separate and move to each pole

TELOPHASE 2

Cell division is complete. 4 haploid (n) daughter cells are produced. All are different due to crossing over

Telophase 1

Cytoplasm is divided and a nuclear membrane forms around each new set of chromosomes. Each new cell is haploid because they contain either the maternal or paternal set of homologous chromosomes

Spermatogenesis

Oogenesis

End with 23 choromsomes

MONOSOMY

TRISOMY

egg with extra 21 choromsome is ferizted by a noral sperm (hapoid). Happens in meosis 1