Aim:Why is meiosis important?

• Do Now: Label each phase of cell division (IPMATC)

So, what is the difference between

mitosis and meiosis?

Mitosis• 2 identically

diploid cells (same as parent)

• Makes cells used for growth, repair, development & asexual development

Meiosis - 4

genetically different haploid cells

- Makes cells for Sexual reproduction

- Genetic info is exchanged/rearranged.

Meiosis I

• Contains all phases of mitosis

• Homologous chromosomes separatedI P M A T CI

PrayMoreAt The Church

Interphase I• This is where

the chromosomes are duplicated, replicated, or copied.

Eukaryotic Cell Cycle

Prophase I• Chromosomes

condense. The nuclear envelope breaks down.

“Crossing Over” occurs.

• “Crossing Over”-Chromatids exchange genetic material

Metaphase I

• Pairs of homologous chromosomes move to the cell’s middle.

Metaphase = Move Middle

Anaphase I

• Homologous chromosomes move to the cell’s opposite poles.

Telophase I

• Chromosomes gather at the poles.

• The cytoplasm divides.

What about cytokinesis?• In cytokinesis, the nuclear membrane is

reforming around each new cell.

Cytokinesis happens after the division of

chromosomes and cells are made.

Meiosis IINO

INTERPHASE and NO

REPLICATION of

chromosomes!!

P M A T

Prophase II

• A new spindle forms around the chromosomes.

Metaphase II

• Chromosomes line up at the middle.

Anaphase II

• Centromeres divide, and chromatids move to opposite poles.

Telophase II

• A nuclear envelope forms around each set of chromosomes. The cells divide.

What do we end up with at the end of meiosis?

• 4 haploid cells?

Answer to Aim:Why is meiosis important?

• Allows genetic information from 2 parents to combine to form offspring that are different from both parents.

What is a homologous chromosome?

Chromosomes that have the same sequence of genes, that

have the same structure, and that pair during meiosis.

Chromatid is a single strand of chromosomes.

Chromosomes are 2 chromatids together, made of condensed chromatin.

Centromere is where the two chromatids meet.

Chromatin are ribbon-liked structures of DNA and histone proteins.

Label the chromosome

• “Crossing Over”-Chromatids exchange genetic material

• Tetrad- a pair of homologous chromosomes.As the tetrads

form, the chromosomes exchange parts of their chromatids during the process of crossing over.

• Crossing over is one of the several processes that lead to genetic variation.

• The rearranging of genetic info leads to genetic variation in offspring.

Activity in text page 253 on crossing over.