LEARNING OUTCOMES• To state the necessity of trait inheritance in

offspring for continuation of life,• To state the necessity to maintain diploid

chromosomal number from generation to generation,

• To state the necessity for production of haploid gametes in sexual reproduction,

• To state the significance of meiosis,• To identify the type of cell that undergoes

meiosis,• To explain the process of meiosis,• To arrange the various stages of meiosis in the

correct order,• To compare and contrast meiosis I & meiosis II,• To compare and contrast meiosis & mitosis.

MEIOSIS• A division of the nucleus to produce 4 daughter

cells each containing half the chromosome number of the parent nucleus.

• A type of cell division - occurs in reproduction organs to produce 4 daughter cells called gametes.

• The process of nuclear division that reduces the number of chromosomes in new cells to half the number of chromosomes in the parent cell.

• Each daughter cell receives 1 set of chromosome from each pair of homologous chromosomes – haploid cell (n)

MEIOSIS• Genetic material in the gametes differs

from the parent cell & each other

• Animals : testes in males – sperm ovaries in females – ovum

• Plants : anthers – pollen (male gametes)ovaries – ovules (egg cells)

• Consists of Meiosis I and Meiosis II

THE SIGNIFICANCE OF MEIOSIS

• To allow trait inheritance in offspring – the transmission of traits

• To maintain diploid number in each generation - the organisms are always diploid

• To ensure the production of haploid gametes in sexual reproduction

• To produce genetic variation among offsprings

MEIOSIS• Meiosis I : the homologous chromosomes

are separated into two haploid daughter cells

• Meiosis II : the sister chromatids of each daughter cell are separated.

• Meiosis II = mitosis in a haploid cell

• All chromosomes are replicated during interphase sister chromatids joined at centromere. The chromosomes do not replicate again between Meiosis I & Meiosis II

MEIOSIS IPROPHASE I

• Centrioles move to opposite poles.• Chromosomes thicken & condense• The homologous chromosomes form

bivalent through synapsis• Crossing over happened : non-sister

chromatids exchange segments of DNA new combination of genes on a chromosome

• Chiasmata – the points at which segments of chromatids cross over

• Nucleus membrane & nucleolus disappear• Spindle fibres are formed

METAPHASE I• The paired chromosomes are lined

up at the equator of the cell

• One chromosome of each pair faces each pole of the cell

• the chromosomes attached to the spindle fibres at their centromere

• The centromere does not divide

ANAPHASE I• The paired chromosomes separate from

one another & move to opposite poles

• The spindle fibres pulled one chromosome of each pair to each pole

TELOPHASE I• The chromosomes arrive at the poles.

• Each pole has a haploid daughter nucleus (contain one set)

• The spindle fibres disappear, the nuclear membrane & nucleolus reappears in each nucleus.

• Cytokinesis occurs

• No interphase, no replication of chromosomes

MEIOSIS IIPROPHASE II

• Centriole duplicates & move to opposite pole

• Nuclear membrane disappear, spindle fibres re-form

• The chromosomes move to the equator of the spindle.

METAPHASE II• Chromosomes lined

up at the equator of the cell facing opposite poles

• Each sister chromatid is attached to the spindle fibres at the centromere

ANAPHASE II• The sister chromatids

together split

• Chromatids separate

• Spindle fibres pull each chromatid to opposite poles

• Centromere are divided

TELOPHASE II• Chromatids reach the poles &

become new chromosomes

• Nuclear membrane & nucleolus form again at each chromosome

• Chromosomes become extended & not visible

• Cytokinesis occurs & 4 haploid daughter cell are formed.

THE COMPARISON BETWEEN MEIOSIS I & MEIOSIS II

MEIOSIS I SIMILARITIES MEIOSIS II

•Consist of 4 stages : P,M,A,T•Involve division of nucleus & cytokinesis

DIFFERENCES

Occur Synapsis Not occur

Yes Cross over No

MI-paired homologous chromosomes line up

at the equator

Metaphase MII – each chromosome with sister chromatids line up at the equator

AI – paired homologous chromosomes separate

& move to opposite poles

Anaphase AII – the sister chromatids separate & move to opposite poles

2 haploid cells are formed

At the end 4 haploid cells are formed

THE COMPARISON BETWEEN MITOSIS & MEIOSIS

MEIOSIS SIMILARITIES MITOSIS•Division of cells

•The chromosomes replicates only once

DIFFERENCES

In reproductive organ Place occur In somatic cell

Parent cell divides twice Number of divisions Parent cell divides once

Four haploid daughter cells Number of daughter cells Two diploid daughter cells

Occurs during prophase I Synapsis of homologous chromosomes

Not occurs

Occurs twice Number of cytokinesis Occurs once

Occurs during prophase I Crossing over of chromatids of homologous chromosomes

Not occurs

Half of number of chromosomes of the parent cell (haploid)

Number of chromosomes in daughter cells

Genetically identical to the parent cell

Genetically non-identical to the parent cell & each other

Genetic composition of daughter cells

Genetically identical to the parent cell

Occurs once during interphase before meiosis I

DNA replication Occurs during interphase before mitosis begins