The information that results in plants and animals having similar characteristics to their parents is carried by genes, which are passed on in the sex cells (gametes) from which the offspring inherit.
The gametes join and fuse together furing fertilisation. Fertilised eggs have two sets of genes, which will control the development of characteristics we inherit.
Genes are linked together in long thread-like structures called DNA. It is made from two strands, which are twisted together to make a spiral. This is called a double helix.
The nucleas of a cell normally has two sets of chromosomes in it. Genes and chromosomes are made from a chemical called DNA. We obtain one set from our mothers egg and the other from our fathers sperm. Humans have 48 chromosomes in each nucleas so each set has 23 chromosomes.
Causes of Variation
Difference in the characteristics of any different individuals of the same species may be due to a range of factors.
Environmental and inherited characteristics
Some characteristics of an individual are caused by the enviroment. For example, the language we use or whether we have scars are known as enviromental characteristics.
Here are some inherited characteristics:
- The shape of the earlobes
- Eye colour
- Nose shape
Some characteristic - including intelligence, body mass and height - are a result of both enviromental and inherited factors.
Genotype - The full set of genes of an organism
Phenotype - the observable characteristics of an organism
Asexual Reproduction only involves one parent. it is very common in smaller animals and bacteria, although it does occur in larger plants such as daffidils or strawberries. Bulbs, corns or tubas are all ways in which plants can reproduce asexually.
During asexual reproduction there is no joining of sex cells. The offspring contain identical genetical information to their parents. The offspring therefore do not show variation. All offspring are identical to each other and to their parents. Such identical offsring are called clones.
This process involves the fusion of a male sex cell (sperm in animals) with a female sex cell (egg) from two different parents. These two special cells or gametes will join to form a new individual. The gametes only contain half the number of chromosomes found in a normal body cell. They have one of each type of chromosome not two of each type as found in body cells.
At fertilisation, when the sperm and egg fuse, a fertilised cell or zygote is produced with the full number of chromosomes (half from the egg and half from the sperm). hence the new individual will show some of the same characteristics of each parent as it has recieved a mixture of chromosomes from both parents. This introduces variation. Variation in a species is very important for its survival. The more variety in a population, the more likely it is that some individuals will survive different conditions; if they were all identical they could all be killed.
It is more risky than asexual reproduction as it relies on two gametes from two different individuals meeting.
Cloning - Taking Cuttings
- Remove a small section of the parent plant
- Dip into rooting powder to encourage root growth
- Place soil in pot and place cutting into the soil gently
- Water the soil
- Put a plastic bag over tha plant with a hole cut into the corner
- The hole allows air in and prevents mould from growing
- Leave on a sunny window soil
- A small amount of parent tissue or a number of cells is taken and the surface sterilised.
- The tissue is transferred to a sterile nutrient jelly called agar.
- Auxins (growth homrones)are added to stimulate the cells to divide by mitosis.
- Cells grow rapidly into small masses of tissue (called a callus).
- More growth hormones (a different combination) are now added to stimulate te growth of roots and stems
- The tiny particles are transferred into potting trays where they develop into plants
Advantages: Produces lots of plants less quickly, easier, only need a small amount of cells
Disadvantages: Slow, technical, has to use sterile equipment, requires training/special equipment
- Genetically the same
- Fertilised egg splits into 2
- Same Sex
- Not genetically the same
- 2 eggs fertilised by 2 sperm
- Boy/girl, Girl/girl or Boy/boy
There are two methods of animal cloning: Embryo Splitting and Nuclear Transfer
Step 1: An egg from the mother and the sperm from the father are removed the joined together
Step 2: The fertilised egg will grow in a lab into an embryo
Step 3: Then the embryo will be split up and grow as identical embryos in a lab
Step 4: The embryos will then be transferred into the host mothers and identical lambs are born
This type of cloning is useful as they can copy very high producing animal that is too old to breed or unable to breed.
Adult Cell Cloning
A well known case of Adult Cell Cloning is Dolly the Sheep.
1) Cell is taken and was placed with an agg from a donor sheep.
2) The nucleas was taken from the cell and the nucleas removed from the egg.
3) The empty egg is fused together with the nucleas of the cell by a mild electric shock.
4) The embryo is implanted in a host mother.
5) A clone sheep is born i.e. Dolly.
These embryo cells contain the same genetic information as the adult skin cell.
- To replace loved ones
- To clone the most desirable cattle
- To prevent species extinction
- Cloning mammals is a means providing organs for transplants.
Adult Cell Cloning
- It raises social and ethical issues.
- Cloning mammals produces a reduced gene pool. This can make the species more susceptible to a contracted disease and other conditions such as premature aging, organ and immune system failures etc.
- The rate of successful cloning very low, genetic defects are common and those animals which survive the cloning procedure are often unhealthy and are much more susceptible to disease i.e. they are a 'genetically weak' animal.
- If human cloning was attempted, it could lead to babies being born with disabilities, there is only a certain chance that an embryo would develop into a completely normal healthy baby - an ethical and moral dilemma for potential parents and the medical profession.
- Aged DNA of clone - would we see earlier onset of 'old age' diseases?
GM Foods - Advantages
- GM crops would need fewer chemical sprays. Makes them more resistant to herbicides - Makes them less likely to be poisoned by the herbicides and crops won't be destroyed
- Makes them produce chemicals to stop insects eating them - More crops can be made that aren't damaged and won't have to use pesticides, better for the enviroment
- Produces an increased yield of crops. Could result in cheaper food - We can have a lot of food to eat and wouldn't have to grow as often. More food to feed the world.
- Could grow in harsher conditions
- Could reduce biodiversity
- New proteins in GM crops could cause allergies
- GM seeds are expensive
- Accidental transfer of new genes to other plants
Genetic Engineering can be used to make living things produce other, more valuable products. Genetic Engineering is changing the DNA of a living thing to change its characteristics.
Stage 1: Select the roduct or characteristic needed
Example: antigen from hepatitus B
Stage 2: Isolate genes from specialist cells
Example: hepatitus B virus
Stage 3: Insert the genes into target cells
Stage 4: Replicate the new organism
Example: Yeast culture in fermenters
How bacterium can be genetically engineered to produce human insulin?
- Many bacterial cells contain rings of DNA called plasmids. These plasmids can be used for genetic engineering
- The gene that controls insulin is cut out of human DNA by special 'chemical scissors' called a 'restriction enzyme'
- The same enzyme can cut open a plasmid
- The human insulin gene is then inserted in the plasmid
- Another enzyme called 'ligase' joins the two ends of the insulin gene to the but ends of the plasmids
- The plasmid has been recombined with the insulin gene. This is called 'recombinant plasmid' or 'recombinant DNA'
- The recombinant plasmid has now been put back into the bacterial cell. This can be done by a small, short, electrical shock to the bacterium
- This makes very small, temporary holes in the bacterium cell wall. The recombinant plasmid quickly passes through the holes before they close up again
- The bacteria that contains recombinant DNA will start to produce lots of insulin but only if they are given the right conditions