Section 8-3 Meiosis

Obj 9: List and describe the phases of meiosis

Meiosis I: Preceded by copying of DNA in interphase

Prophase I

Homologous chromosomes pair each pair = tetrad (4 chromatids) Crossing-over may occur

Chromatids twist around each other & parts are exchanged (genetic recombination)

Metaphase I

tetrads line up

Anaphase I

chromosomes move to opposite poles independent

assortment - random separation of chromosomes, resulting in genetic variation

Independent assortment http://10.20.0.2/videos/pmp/videos/wm

/1MB/8VH0457G_1Mb.wmv

Telophase I

chromosomes reach opposite poles

cytokinesis forms 2 cells

Meiosis II

Not preceded by copying of DNA Occurs in both cells Same 4 phases - prophase II,

metaphase II, etc.

Meiosis II

Difference: In anaphase II,

chromatids separate (not chromosomes)

Obj 10: Compare the products of mitosis with those of meiosis

Both from a 2n parent cell:

Mitosis produces 2 diploid (2n) daughter cells

Meiosis produces 4 haploid (1n) gametes

Meiosis

Obj 11: Explain crossing-over and how it contributes to the production of unique individuals

During pairing up, chromosomes exchange DNA results in new

(unique) genetic combinations

Obj 12: Summarize the major characteristics of spermatogenesis and oogenesis

Spermatogenesis: Cytoplasm

divides evenly and produces 4 haploid cells

Spermatids grow flagella and are oval

Oogenesis: Cytoplasm divides

unevenly Egg receives

majority of cytoplasm

Polar bodies receive little cytoplasm will die and are

absorbed