Chapter 13

Meiosis & Sexual Life Cycles

Vocabulary• genome – an organism’s complement of DNA

• gene – segment of a chromosome that codes for one polypeptide

• asexual reproduction – a single individual gives rise to genetically identical offspring (clone)

• sexual reproduction – 2 parents give rise to

offspring having DNA from each parent

Human karyotype

Vocabulary

• somatic cell – body cell; not a sex cell

• gamete – sex cell (egg or sperm)

• diploid – a cell with 2 copies of the genetic material (2n)

• haploid – (monoploid) a cell with one copy of the genetic material (1n)

Vocabulary• autosomes – chromosomes other than sex

chromosomes

• sex chromosomes – X and Y usu.

• zygote – cell created from the union of sex cells

• fertilization (syngamy) – union of gametes

• alternation of generations – alternating between diploid and haploid stages in the life cycle

• sporophyte – diploid stage (2n)• gametophyte – haploid stage (1n)

Meiosis

• DNA replicates during interphase I prior to meiosis

Meiosis I

Prophase I – formation of 4-stranded groups

(tetrads) during synapse, DNA crossing over

between homologues occurs at chiasma,

nuclear membrane, nucleolus breaks down,

centrioles migrate to poles, spindle forms

MeiosisMetaphase I - tetrads line up at equator

Anaphase I – tetrads separate; homologues move to opposite poles

Telophase I – nuclear membrane, nucleolus reappear, cytokinesis follows

Meiotic interphase – no DNA replication

Meiosis

Meiosis II like mitosis

Prophase II

Metaphase II

Anaphase II

Telophase II

Meiosis

• Result: 4 haploid daughter cells

through spermatogenesis or oogenesis

(gametogenesis)