Science 9: Unit A

1
Science 9 Unit A Biological Diversity

• Topic 5 When Plans Change

2
DNA is the Genetic Code for Life

• DNA Deoxyribonucleic acid.
• DNA is a chemical found in the nucleus of all
  cells.
• DNA forms long strands called chromosomes. Every
  cell in a human has 46 chromosomes in its
  nucleus.
• 23 chromosomes come from our fathers, and 23 from
  our mothers.

3
The Structure of DNA

• DNA is in the form of a coiled ladder.
• The rungs of the ladder are made up of pairs of
  chemicals called nitrogen bases. There are four
  different nitrogen bases.

4
The Four Nitrogen Bases

• The chemical rungs are four nitrogen bases
  Adenine (A), Thiamine (T), Guanine (G), and
  Cytosine (C).
• The rungs of DNA are made up of alternating pairs
  of these bases.
• Adenine can only pair up with thiamine, and
  cytosine with guanine.
• The pattern of these repeating pairs makes up our
  entire genetic code.

5
DNA, Proteins, and Genes

• DNA forms chromosomes. Different sections of
  chromosomes act as blueprints for different
  proteins to be made.
• A section of a chromosome that codes for a single
  protein is called a GENE.
• A single chromosome can have hundreds or
  thousands of genes, made up of billions of base
  pairs.
• All cells and tissues are made up of proteins.

6
The Discovery of DNA

• Canadian scientist, Oswald Avery discovered DNA,
  but could not figure out its structure or see it
  in a microscope.
• Watson and Crick, an English and American duo
  discovered DNAs structure. Their model explains
  how just four nitrogen bases can account for all
  of the biological diversity in the world.

7
Layout of Chromosomes

• DNA is organized into chromosomes in a cells
  nucleus.
• The chromosomes are organized into pairs. So
  humans have 23 pairs of chromosomes, one from
  each parent.
• Each chromosome in a pair has genes that code for
  the same protein, however, only the dominant one
  is switched on.

8
Whats an allele?

• An allele is a form of a gene. For example, the
  number of fingers on your hands is based on a
  gene. There is more than one allele for that
  gene. You can have 5 fingers (recessive allele)
  or 6 fingers (dominant allele)
• Something like hair color can feature many genes
  so that a child from brown and blonde haired
  parents will have dirty blonde hair.
• So for every gene you have, you have an inactive
  allele.

9
Mitosis is Cell Reproduction for Somatic Cells

• Is how somatic cells (non-gametes) reproduce in
  our body. It works like binary fission.
• Step 1 The chromosomes in the parent cell
  nucleus clone themselves.
• Step 2 The chromosomes all line up in the centre
  of the nucleus.
• Step 3 The nucleus splits up and the cell
  stretches.
• Step 4 The chromosome twins split apart, going
  in opposite directions.
• Step 5 The cell membrane pinches off, producing
  two daughter clone cells, each with the same
  number of chromosomes as the parent cell.

10
Meiosis is Cell Reproduction to Form Gametes

• Is how gametes are formed. Gametes must have half
  the of chromosomes of a regular cell since they
  will be combining with each other in sexual
  reproduction.
• This process is achieved by having a regular cell
  divide twice. This produces four gamete cells
  each with only half the chromosomes of the parent
  cell.

11
Meiosis and Mutations

• During meiosis, genes are swapped between
  chromosomes so that the chromosomes are now
  different. This further increases variation in a
  species.
• Your fathers chromosome may have contained the
  allele for brown hair, but during meiosis, this
  may have been switched with the allele (from
  Moms chromosome) for red hair.

12
Genetic Engineering

• Is the process of taking the genes of one species
  and transplanting them into the chromosomes of
  another organism. AKA Gene splicing.
• Eg. Certain plants have been given the gene for
  disease resistance from insect species.
• These new species of GMOs (genetically modified
  organisms or foods) are extremely controversial
  as people do not like the idea of scientists
  tampering with nature.