Title: Cell cycle (again)

Objectives: Today we are learning to answer the following questions:

• What are the various stages of the cell cycle• Explain the meaning of the term homologous pair of

chromosomes• What is meant by sister chromatids• Describe with the aid of diagrams the main stages

of mitosis.

What is DNA ?

What is the point of genetic material?

What is a gene?

DNA (Deoxyribonucleic acid)

Provides a code that codes for proteins, controls activity of the cell

A sequence of DNA that codes for one protein

• DNA is held on chromosomes• Made of DNA & histone proteins = Chromatin

• Humans have 46 chromosomes arranged in 23 homologous pairs

• Homologous pair – 2 chromosomes that contain the same genes; humans = 1 maternal, 1 paternal

• The number of chromosomes varies between species

Sister Chromatids = 2 identical chromatids connected by a centromere.

Original and replicated strand joined at the centromere

The Chromosomesreplicate during interphase

Homologous chromosomes

Put the stages of mitosis in order

Then answer the questions:

1.When a cell divides by mitosis how many cells are made?

2.Comment on the similarities and differences of daughter cells to each other and the parent cell.

3.Species such as yeast reproduce by cell division, Describe the genetic make up of yeast colonies.

The process of creating 2 genetically identical daughter cells from 1 parent cell = MITOSIS

Division of somatic (body) cells is by mitosis – remember • Mitosis make two cells• Mitosis makes toes

What is happening at each stage of the cell cycle?

How many chromosomes are in the nucleus during each stage?

June 2009

Why do cells need to divide?What are the processes by which cells divide?

1. Growth (mitosis)2. Repair damage (mitosis)3. Replace worn out cells (mitosis)

4. Gamete creation (meiosis)

Chromosomes visible with light microscope

Chromosomes visible with light microscope

Chromosomes visible with light microscope

Chromosomes visible with light microscope

Chromosomes are not visible with light microscope

Prophase

Metaphase

Anaphase

Telophase