DNA: CHROMATIN AND CHROMOSOMES

DNA: CHROMATIN AND CHROMOSOMES

DIPLOID AND HAPLOID CELLS

MITOSIS

WHAT IS THE AIM?

To deliver the same genetic material to daughter cells during cell division.

TO DELIVER THE SAME GENETIC MATERIAL

1. DNA replication.

2. DNA organize forming chromosomes.

3. During mitosis chromatids are delivered to different daughter cells.

MITOSIS GENERAL SCHEME

MITOSIS: PHASES

INTERPHASE:

DNA replication.

Centriole replication

Chromatin in the nucleus.

MITOSIS: PHASES

PROPHASE:

Chromosomes (2 chromatids) can be seen in the nucleus.

Centrioles start forming mitotic spindle.

MITOSIS: PHASES

METAPHASE:

The nucleus disappear.

Mitotic spindle attaches to chromosomes centromere.

Chromosomes align in the centre of the cell

MITOSIS: PHASES

ANAPHASE:

Chromatids split up and are delivered by the mitotic spindle to separate poles of the cell.

MITOSIS: PHASES

TELOPHASE:

New nuclei start forming around the chromosomes.

Chromosomes turn to chromatin.

Cytokinesis.

MEIOSIS

What are the aims?

To get haploid cells. GAMETES.

Each gamete is going to be genetically unique. This is possible because of the genetic recombination or crossing over.

To get haploid cells from diploid cells two cell divisions are needed.

FIRST MEIOTIC DIVISION

PHASES: INTERPHASE I

DNA replication.

Centriole replication

PHASES: PROPHASE I

Chromosomes appear and form tetrads.

Random exchange of fragments (crossing over) or genetic recombination.

Nucleus starts disappearing and centrioles form meiotic spindle.

PHASES: METAPHASE I

Pairs of homologous chromosomes bond to the meiotic spindle.

PHASES: ANAPHASE I

Complete chromosomes are pulled to opposite cell poles thanks to the meiotic spindle.

Chromosomes are genetically different after crossing over.

PHASES: TELOPHASE I

SECOND MEIOTIC DIVISION

After first meiotic division daughter cells have chromosomes with two chromatids, so the second division split up the chromosomes to obtain chromosomes with one chromatid.

Second meiotic division occurs following the same phases than mitosis but without DNA replication.

SECOND MEIOTIC DIVISION

MEIOSIS GENERAL SCHEME

MEIOSIS GENERAL SCHEME