Meiosis and Sexual Life Cycles

Autosomes

: 22 pairs of chromosomes that do not determine sex.

genetic material

Crossing Over: exchange , resulting in recombinant chromosomes.

Sporophyte

(2n): makes haploid spores by meiosis.

Zygote

divides by mitosis to make multicellular diploid organism.

Meiosis

: cell division that reduces of chromosomes (2n → n), creates gametes.

Synapsis

: homologous chromosomes pair up.

Interphase

: chromosomes replicated.

Metaphase

I: pairs of homologous chromosomes line up on plate.

Fertilization

: combine gametes (sperm + egg)

homologous pairs

Anaphase I: separate → sister chromatids still attached at centromere.

Gametophyte

(n): makes haploid gametes by mitosis.

Life cycle

: reproductive history of organism, from conception → production of own offspring.

Little variation in population

only through mutations

2 parents

male/female

Somatic (body) cell

2n = 46 chromosomes

Autosomes

22 pairs of chromosomes that do not determine sex

Sex chromosomes

X and Y

Females

XX

Males

XY

Gametes (n=23)

22 autosomes + 1 sex chromosome

Egg

22 + X

Sperm

22 + X  or 22 + Y

Life cycle

reproductive history of organism, from conception → production of own offspring

Meiosis

cell division that reduces of chromosomes (2n → n), creates gametes

Fertilization

combine gametes (sperm + egg)

Sporophyte (2n)

makes haploid spores by meiosis

Gametophyte (n)

makes haploid gametes by mitosis

Interphase

chromosomes replicated

Synapsis

homologous chromosomes pair up

Tetrad

4 sister chromatids

Metaphase I

Tetrads line up

Some species

chromatin & nucleus reforms

Prophase I

Synapsis and crossing over

Metaphase I

pairs of homologous chromosomes line up on metaphase plate

Anaphase I

homologous pairs separate → sister chromatids still attached at centromere

Crossing Over

exchange genetic material, resulting in recombinant chromosomes

Independent Assortment of Chromosomes

random orientation of homologous pairs in Metaphase I

Random Fertilization

Any sperm + Any egg