Biology Topic 1

Mitosis Makes New Cells For Growth and Repair 

• Human body cells are diploid, this is where they have 2 copies of each chromosome. One comes from the mother, the other from the father.
• When the cell divives it needs to make 2 cells identical to the orginal, with the same amount of chromosomes. This is called Mitosis.
• Its used when humans, animals and plant want to grow or replace cells that have been damged.

Mitosis Produces Two Identical Cells

• DNA is copped to form X-Shaped chromosomes.
• The cell divdes causing the chromosomes to be riped apart.
• There are now 2 diploid cells containing exactly the same DNA - they are genteically identical.

Asexyal Reproduction Also Uses Mitosis

• Some organims reproduce by mitosis which is an example of asexual reproducction.
• The offsprung have the same genes as the parent, making  no gentic varation. 

Gametes Have Half The Usual Number of Chromosomes

• Gametes are sex cells; Ova in females and sperm in males.
• During sexual reproduction, two combine to from a new cell.
• Gametes are haploid, meaning they have one copy of each chromosome. When two combine at fertilisation a zygote forms with the correct amount of chromosomes.
• Zygotes are diploid.

Meiosis proudces Four Different Cells

Meiosis only happens in reproductive orgains and the cell divides to produce 2 hapoild cells, whose chromosomes are not identical.

• Like in mitosis, DNA is copied to make X-Shaped chromosomes
• Cell divides with some of the father and some of the mothers chromosomes in each cell. This means there is a mixture of chromosomes.
• Each cell fives again and the X-shaped chromosomes are pulled apart.
• You end up with 4 haploid gametes, each wih 1 copy of each chromoxsomes in but genetically different. 

Cloning has Many Uses 

• It is a type of asexual reproduction that produces cells genetically identical to the orignal.
• Clong can helo towards the sortage of organs for transplants.
• Studying animal closes could improve our understanding of things like ageing, age-related disorders and the development of embryos as well as helping towards preserving endangered species.

There are Issues Invovled

It can lead to a reduced gene pool, meaning fewer alleles in a population.

• If a population is closly related and a new disease appears, they could be wiped out as there is no allele giving resistance to the diesease in the poulation.

Cloned mammals don't live as long

• Dolly the sheep lived for half as long as other sheep due to a lung diease, common in older sheep or she might have been unlucky. 

There are other risks and probelms

• Clones may be born with gentic defects,
• The cloning process may fail
• Cloned mammals immune systems are sometimes uhealthy so they suffer from more diseases. 

Embryonic Stem Cells Can Turn into Any Type Of Cell

• Fertilised eggs can dividie producing bundles of cells, the embryo if a new organiamas.
• To start with, the cells inside are alll the same and are called embrynoic stem cells. These are able to divide, producing different types of specialised celles. This is called diffrentiation
• In most animal cells, differentation is lost at an early stage.
• Adult humans have stem cells in certain places like bone marrow and they aren't as useful as the stem cells in embryos as they can only differentiate into certain types of cells.

Stem Cells May be Able to Cure Many Diseases.

• Doctors Use adult stem cells to cure diseases.
• Scientists experiment with taking stem cells from early human embryos and growing them
• Under certain conditions, the stem cells will differentiate into speicalised stem cells, it may also be possible to use these cells to replace those damaged or injursed.
• Research needs to be done which causes concerns...(see next card)

Ethican Concerns about stem cell researh:

• Some people are strongly against it as they see each embryo as one human lige.
• Other people believe that curing patients is more important than the potential lifes of embroyos.
• Stem cell research is banned is some countries but allowed, under strict guidelines, in the UK.