Inheritance

Sex cells

The male sex cell is sperm. It is made in the testes.

Part FunctionSperm Tube carries sperm to penisPenis allows sperm to travel outside the bodyTestis where sperm is made

The female sex cell is the egg. The egg is found in the ovaries.

Part FunctionOviduct where eggs are fertilised by spermOvary where the eggs are released fromVagina the man’s penis enters here during sexual intercourseUterus where the baby develops (also known as the womb)The egg and sperm cells are known as gametes.

Fertilisation

Fertilisation is when the nucleus of a sperm and egg cell fuse together and produce a zygote, which then develops into an embryo (after 8 weeks). Fertilisation occurs in the oviduct. Genetic Information

Inside the nucleus of a cell there is genetic material called chromosomes.

sperm duct

A chromosome is a threadlike structure that carries genetic information.

The chromosome complement is the number of chromosomes an organism has. Most humans have 46 chromosomes , 23 pairs one set from the mother and one form the father.

Chromosomes are made of long coiled up molecules called DNA.

Gene is a section of a chromosome which contains a separate piece of genetic information and codes for specific characteristics.

DNA stands for deoxyribonucleic acid and is shaped in a double helix. There are four bases in DNA that hold the two strands together.

Adenine (A) always pairs with thymine (T) (remember AT). Guanine (G) always pairs with cytosine (C).

Extracting DNA

Below are simple steps to extract DNA from strawberries. The text in italics tells you why it’s necessary to do each step.

1. Squash the fruit inside a plastic bag (To break open the cell it and allow the DNA to leak out.)

2. Add salt solution and washing up liquid (To break down the fat and proteins that make up the cell membrane.)

3. Heat the mixture for 15 minutes at 60oC(To speed up the chemical reaction.)

4. Filter the fruit mixture into a boiling tube (To filter out the large insoluble parts of the cell)

5. Gently add ethanol down the side of the boiling tube.(The ethanol causes the DNA to precipitate (form a solid) and so is visible)

Foetal development

The developing foetus is connected to

the mother’s blood supply through the placenta.

The placenta has a very important job as it allows oxygen and nutrients to pass to from the mother to the foetus and allows carbon dioxide and waste substances to pass from foetus to mother.

The mother’s lifestyle can affect the developing foetus too. The smoke from cigarettes reduces the amount of oxygen and so can lead to low birth weights or premature birth. Alcohol can cause harm the baby’s nervous system, especially the brain.

Genotype and Phenotype

Phenotype is the physical appearance resulting from the inherited information e.g. someone with blue eyes has the phenotype blue eyes. (Remember physical phenotype

The genotype is the type of genes an organism carries e.g. BB, Bb, bb (one letter from our mum and one from our dad)

Dominant and recessive genes

Dominant genes are always shown. Only one copy of the dominant gene needs to be present for that characteristic to be to be shown. They are represented by capital letters.

Recessive genes are only shown when two copies of the gene are present. If only one is present it becomes ‘masked’ by the dominant gene. They are represented by lower case letters.

Golden Labrador Black Labrador Black Labrador

Two work out which trait is recessive, concentrate on the dog with the mixed genes. The black Labrador at the end has a gene for black and yellow but it’s phenotype is black; the yellow gene has been masked. From this we can conclude that the black gene is dominant and the yellow gene is recessive.

IVF

In vitro fertilisation (IVF) is a technique used to help people with fertility problems have a baby. An egg is removed from the woman's ovaries and fertilised with sperm in a laboratory. The fertilised egg is then returned to the woman's womb to grow and develop.

Microbes

Bacteria

Useful• process waste in our intestines• Make yoghurt and cheese• Bacteria help to break down faeces in

sewage works. Harmful • Causes tooth decay• Food poisoning – undercooked food

Virus

Useful• For scientists to study genes Harmful• Cause chicken pox, flu, cold and ebola

Fungus

Useful• Good fungi – mushrooms• Used in the production of bread, beer and

wine Harmful• Cause diseases in humans• Makes food go mouldy• Athletes foot from fungal growth

Microbes can be spread by sneezing, coughing, drinking, eating, through cuts or by animals (e.g. bites form mosquitos).

Body Defence

The first line of defence includes the skin, tears, stomach and sticky mucus.

The second line of defence involves our immune system.

Phagocytes engulf and digest bacteria and foreign materials.

Lymphocytes are specialised white blood cells which produce antibodies that attack any invader in the body.

Memory

The first time we have an infection we produce antibodies slowly meaning we will probably get ill.However, the second time we are exposed, antibodies are produced faster so we cope with it better and either won’t get ill or will be ill for less time.

Vaccinations

Dead or weakened form of virus are injected into your body. Your body produces antibodies so when real virus attempts to attack, your immune system immediately recognises and kills it.