Topic 5 – When Plans Change (DNA)

Science 9 - Biodiversity

What is DNA and where do we find it?Each person’s DNA is very different from

others.DNA:Deoxyribonucleic acidComposed of genetic material (inherited

material)Responsible for variationControls the formation of cellsFound in the nucleus of the cell

Watson & Crick figured out that DNA was organized as a double helix

Make-Up of DNA4 chemicals called nitrogen bases (rungs of

the ladder)Guanine – GCytosine – CAdenine – A Thymine – T

Alternating sugar & phosphates (sides of the ladder)

To do:Discovery Streaming Videos – DNA intro &

Genetic Engineering

When you place ATCG into various orders, you can create thousands of different combinations – called genetic code (codes for what we will be like)

One cell contains about 2 m of DNAHow does it all fit into one cell?

The DNA wraps into chromosomes

ChromosomesEach human has 23

pairs of chromosomes (46)

Different species have different numbers of chromosomes

Contain numerous genes

Are inherited from our parents

GenesUninterrupted segment

of DNA which contain coded instructions

Are found on the chromosome

Come in pairs (one from each parent)

Both pairs carry DNA for the same thing Ex: leg length

Different “flavours” of genes are called alleles

Alleles: a possible form of a geneEx: blue or brown

eyes (B or b)

Answer in your notes…In what ways is DNA a code?

Remember…Chromosome = cookbookGene = recipeBase pairs (ATCG) = words

Topic 5Mitosis and Meiosis

Quick Review:What are the 4 base pairs?

Thymine, adenine, guanine, cytosine

What pairs are joined together?AT and CG

What is the outside of the double helix made out of?Phosphates and sugars

How do we grow?Cells divide and multiply in order to grow!

There are 2 different ways in which we go about this:

1. Mitosis (creates all body cells)2. Meiosis (creates reproductive cells)

MITOSIS Draw picture – then add in stepsMitosis has 4 steps:1. DNA replicates (doubles)2. Chromosomes line up along midline3. Chromosomes split to the 2 sides of the cell4. Cleavage occurs

Produces 2 body cells (somatic cells) with the same

number of chromosomes as the parent cell These are DIPLOID CELLS (2n)

Examples of mitosis

Meiosis Draw picture – then add in stepsMeiosis has 8 steps:1. DNA replicates2. Chromosome pairs line up at midline3. Crossover can occur(creates variation)4. Chromosomes split to 2 sides of cell5. Split #16. Chomosomes line up at midline7. Chromosomes split to 2 sides of cell8. Cleavage

Produces 4 sex cells that have half the number of chromosomes as the parent cell

MEIOSISOn what type of cells does meiosis occur?

Egg cellSperm cell

THESE are called HAPLOID CELLS (n)

Think about it…An organism has five pairs of chromosomes.

One of the organism’s body cells divides. How many cells are formed? How many chromosomes does each new cell have?

How many chromosomes would be in each sperm cell?

Why do the body cells of all organisms that reproduce sexually have even numbers of chromosomes?

The Benefits of VariationWhat is a benefit of asexual reproduction?

What is a benefit of sexual reproduction?

Which type of reproduction is better for offspring survival?

What does variation mean?

Technology and VariationRead pg. 53-54Define:

Genetic engineeringBiotechnologiesTransgenicAquaculture

Make notes that are 2-3 points on the following 3 titles:Biotechnology in MedicineBiotechnology in Food ProductionA Cost-effective Crop

“Modelling DNA” activity