Biology-Year 9-Inheritance

DNA is a molecule that contains the instructions for your characteristics. DNA is found in chromosomes which are found in the nucleus of cells.

DNA is made up of nucleotides (which is a phosphate, sugar and a base all joined together by strong bonds) and there are 2 of them joined by weak hydrogen bonds in a strand of DNA. 

The two nucleotides will make one strand and when they are all together it will create a double helix structure.

The strands can be in any order and they are connected by the sugar.

The bases are Adenine, Thymine, Cytosine and Guanine:

Adenine goes with Thymine.                           Cytosine goes with Guanine.

A gene is a section of a chromosome that codes for a protein.

Proteins make up most of a cells structure and enzymes, which are also proteins.

Enzymes control chemical reactions in cells.

Three bases code for 1 amino acid (e.g AAT, CCG, AAA, TCG) and amino acids join together to make proteins.

The order of the bases determines the order the amino acids are put together to make protein.

A list of all the bases in order is called the genome of an organism.

Different letter show different characteristics or genes.

Lower case letters are recessive and capitals are dominate genes.

When there are the same alleles (AA) it is called homozygous.

When there are different alleles (Aa) it is called heterzygous.

If the alleles are different then the dominate gene will show through in the persons characteristics.

Examples of phenotypes:                          Examples of genotypes:

- Eye colour                                              - BB

- Natural hair colour                                  - Bb

- Skin colour                                             - bb

- Freckles 

The project was started in 2001 and work is still being continued so that they can identify all the genes in the human genome. It's a collaborative project between scientist in 18 countries. Its aims were to:

• Work out the order/sequence of all 3 billion base pairs in a human genome.
• Identify all the genes
• Develop faster methods of sequencing DNA

Each person has a unique sequence of DNA, unless you have an identical twin.

Benefits of knowing about DNA profiles:

• Improving genetic testing and forensic science
• Locating the genes that are linked to inheriting a disease/Cures for genetic illnesses
• New gene therapy treatment
• Knowledge of how humans evolved 
• Personalised medication

Men have one X chromosome and one Y chromosome. Their sperm can either contain X or Y chromosomes.

Women have 2 X chromosomes and their eggs always have X chromosomes.

Gametes have half the normal amount of chromosomes which is 23 (rather than 46).

By using Punnett squares we can see that there is a 50/50 percentage chance of having a female or male child.

A sex-linked trait is a trait that is gained through sexual contact and is only found in X chromosomes and not Y.

Sex-linked diseases are more common in males because the X chromosome show through even if the allele is resessive because it is the only X chromosome in the males DNA. Where as a woman needs to have both of her chromosomes to be resessive for it to show through.

There are 4 blood groups A, B, AB & O.

You can found out what blood group offspring will be in by using a punnet square.

What alleles creates what blood type:

A + A = A

B + B = B

A + B = AB (this is beacues the alleles are codominant)

A + O = A

B + O = B

O + O = O (This is because type O is recessive)

In the first experiment he crossed two pea plants of different heights - one was tall and one was a dwarf pea plant. All of the offspring were tall. 

He then bred two of the offspring together and then three of the offspring were tall and one was dwarf. Therefore it was in a ratio of 3:1 of tall plants:dwarf plants.

He then realised that the "unit" for the tall plant was dominant over the "unit" for the dwarf plant.

He then experimented with different characteristics such as the surface of the pea and the colour of the pea plant.

What did Mandel establish from his experiments?

• A gene is passed on from generation to generation
  
• A gene has different froms of alleles (two alternate forms)
• An individual must have two alternate forms (alleles) per feature/characteristic
• Each sex cell has one of the alternate two (one of the alleles)
• One allele can be dominate over the other

What have we added to his research?

• Each feature is controlled by a gene, and this is found in a chromosome
• There are 2 copies of each chromosome and gene in all body cells
• But in sex cells they only have one copy of each chromosome and gene
• There are two alleles of each gene
• One allele is dominant over the other allele and this one is called recessive
• When two differnt alleles are in the same cell only the dominant one is expressed
• You can have 2 dominant alleles, 2 recessive alleles or one of each

• Mash up the strawberries into a pulp in a bag.
• In a measuring cylinder, measure out the same amount of washing up liquid and distilled water into a beaker.
• Add salt and mix slowly so no bubbles are created.
• Pour the mixture into the bag slowly to not make bubbles.
• Mix the strawberries and mixture together with your fingers on the outside of the bag and tie it up.
• Put the bag in a 60°C water bath for 15 min. 
• Rince the glass beaker and then put some ice in it.
• Remove the fruit bag once it has been in the bath and put it straight onto the ice then put more ice on top of it.
• The filter some of the fruit mixture into a test tube.
• Put the same amount of ethanol/alcohol into the test tube, do this by slowly pouring it down the side.
• Leave it for a few minutes and you will see a white stringy layer between the 2 liquids. This is the DNA.

Why do we crush the strawberries?

- To break the cell wall

Why do we use washing up liquid?

- It breaks down the cell membrane

What does the salt do?

- It causes the DNA to precipitate (separate) from the solution

Why does the mixture need to be cool?

- It slows down the emzymes that would digest the DNA

What does the cold ethanol/alcohol do?

- It dissolves everything except the DNA so we can see it better. We can't use room temperature alcohol as it won't make more DNA visible.