Meiosis

MeiosisGamete

Formation

VocabularyGametes = sex cells (eggs, sperm)Homologous chromosomes =

paired chromosomes (maternal and paternal) that have the same genes

Haploid = Having only one copy of each chromosome (as opposed to diploid, which has two copies of each)

Such chromosome pairs are called homologous chromosomes

(1) Homologues

(2) Alleles - different forms of a gene for a particular trait may occur in homologous chromosomes

anther (where sperm originate)

ovules inside ovary (where eggs originate)

Overview of Meiosis

A. Meiosis - cell division in which the chromosome number is reduced from diploid and gametes are formed

Happens in GAMETES only!!!

Major Events in Meiosis

Meiosis I Produces Diploid Cells

Meiosis II Produces Haploid Cells

PROPHASE I

METAPHASE I ANAPHASE I

TELOPHASE I

Stages of Meiosis

A. Prophase I

1. Synapsis - replicated chromosomes form tetrads

PROPHASE I

METAPHASE I ANAPHASE I

TELOPHASE I

B. Metaphase I - tetrads are aligned at the spindle equator

PROPHASE I

METAPHASE I ANAPHASE I

TELOPHASE I

C. Anaphase I - tetrads split and sister chromatids move toward the spindle poles

PROPHASE I

METAPHASE I ANAPHASE I

TELOPHASE I

D. Telophase I - each daughter cell has a haploid chromosome set

PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II

E. Meiosis II - sister chromatids separate

Meiosis and Genetic Variation A. Crossing over - the exchange of corresponding segments of homologous chromosomes during prophase I

Mitosisand

MeiosisCompare

d

GROWTH MEITOSIS I,CYTOPLASMIC DIVISION

MEIOSIS II,CYTOPLASMIC DIVISION

spermatids (haploid)

secondary spermatocytes

(haploid)

primary spermatocyte

(diploid)

spermato-gonium

(diploid male reproductive

cell)

2. Spermatogenesis - formation of sperm cells

a. Results in production of four spermatids

GROWTH MEITOSIS I,CYTOPLASMIC DIVISION

MEIOSIS II,CYTOPLASMIC DIVISION

spermatids (haploid)

secondary spermatocytes

(haploid)

primary spermatocyte

(diploid)

spermato-gonium

(diploid male reproductive

cell)

b. Spermatids develop a tail to become mature sperm

GROWTH MEITOSIS I,CYTOPLASMIC DIVISION

MEIOSIS II,CYTOPLASMIC DIVISION

ovum (haploid)

primary oocyte (diploid)

oogonium (diploid

reproductive cell) secondary

oocyte haploid)

first polar body

haploid)

three polar bodies

haploid)

3. Oogenesis - formation of egg cells in females

a. Results in one large ovum and three polar bodies

MITOSIS MEIOSISOne division Two divisions

Slide 16

Mitosis

Meiosis I Meiosis II

Figure 10.10Page 172-173

MITOSIS MEIOSISTwo daughter cells Four daughter cells areare produced produced

Slide 16

Mitosis

Meiosis I Meiosis II

Figure 10.10Page 172-173

MITOSIS MEIOSISDaughter cells are Daughter cells contain identical to each other varying combinations of and to parent cell chromosomes

Slide 16

Mitosis

Meiosis I Meiosis II

Figure 10.10Page 172-173