B1 Variation, reroduction and new technology

The nucleus of a cell contains thread-like structures called CHROMOSOMES

The chromosome thread carries the GENES

In the nuclei of sex cells (gametes) there is only a single set of chromosomes.
Therefore nuclei of male and female sex cells contain one set of genes

The genetic information from the parents is passed on to the offspring during reproduction . So the offspring cells contains two sets of genes, inherited from both parents

Different genes control the development of different characteristics of the offsprin

The genetic information from the parents is passed on to the offspring during reproduction . So the offspring cells contains two sets of genes, inherited from both parents

Different genes control the development of different characteristics of the offspring 

In most body cells the chromosomes are in pairs. One set came from the female gamete and one set from the male gamete.   GAMETE- sex cell which has half the chromosome number of ordinary cell

The genetic information from the parents is passed on to the offspring during reproduction . So the offspring cells contains two sets of genes, inherited from both parents

Different genes control the development of different characteristics of the offspring 

In most body cells the chromosomes are in pairs. One set came from the female gamete and one set from the male gamete.   GAMETE- sex cell which has half the chromosome number of ordinary cell

ASEXUAL REPRODUCTION -  Does not involve the fusion of gamete, all of the genetic information comes from one of the parents, all of the offspring are gentically identical to the parent so there is little variety

Identical copies produced by asexual reproduction are called clones

SEXUAL REPRODUCTION-  Involves the fusion of sex cells, there is a mixing of genetic information, so the offspring shows variation

IN ANIMALS THE SEX CELLS ARE EGG AND SPERM

Offspring produced by sexual reproduction are similar to both parents but cannot be identical. THat is because they have a combination of two sets of genes

Random mixing of genes lead to variation in offspring. This is important in survival. SOme characteristics may give offspring a better chance of surviving in difficult conditions

Differences in the characteristics of individuals of the same kind, may be due to:
- Differences in the genes they have inherited
- The conditions in which they have developed 
- A combination of both these genetic and evironmental causes

Genes are the most important factor in controlling the appearance of an individual.
Plants may be affeted by lack of light, nutrients or space to grow, the weaker plants may have the same genes as healthier plants but cannot grow well if deprieved of nutrients

Human developement may be affected during pregnancy, if the mother smokes or drinks alot of alcohol, the baby may have small birth weight.

Once animals are born, too much or too little food can alter their characteristics. 

E.g genes may determine if someone has the potential to be a good athlete. However training to develop muscles and eating the correct diet will also alter the athletes body

-Children which are genetically identical to their parents are known as CLONES

-Cloning is used to produce new individuals that are usefull in farming and agriculture

- In plants, the process of cloning can be cheap and effective. Plants can be cloned by taking cuttings and growing them

Taking small groups of cells from part of a plant and growing them under special conditions (TISSUE CULTURE) is more expensive. 

Tissue culture can be used to reproduce large numbers of a rare of top qaulity plant

Embryo transplants are used to clone animals. In this process an embryo with unspeciallised cells is split into smaller groups of cells. Each group of gentically indentical cells is transplanted and allowed to develop in a host animal

Sometimes animals or plants are gentically modified to produce usefull substances before they are cloned.

 containing genetic material that has been artificially altered so as to produce a desired characteristic.

In adult cell cloning the nucleus of an adult cell, e.g a skin cell replaces the nucleus of an egg cell.

1) The nucleus is removed from an unfertillised egg cell, the nucleus is removed from the skin cell and placed inside the empty skin cell

2) The new cell is given an electric shock which causes it to start to divide. The ball of cells is called an embryo

3) The embryo is genetically identical to the adult skin cell

4)Once the embryo has developed into a ball of cells, it is inserted into the womb of a host mother

5)Dolly the sheep was produced by ACC in 1997

Benefits 

Development of cloned animals which have been genetically engineered to produce valuable proteins in their milk, these have been used in medicince.

Cloning can save animals from extinction

Disadvantages

Concerns about ethic of cloning:
Cloning limits the variation in a population, this can be a problem for natural selection if the enviroment changes

Concerns about using this technique to clone humans in the future.

Genetic engineering involves changing the genetic makeup of an organism.

Genes can be transferred to the cells of animals, plants or microorganisms at an early stage in their development

A gene is cut out of the chromosomes of an organism using an enzyme, the gene is then placed in the chromosome of another organism

The genes may be placed in an organism of the species to give it a desired characteristic.

Sometimes genes are placed in different species such as bacterium.

New genes can be transferrred to crop plants

Crops with changes genes are called genetically modified crop plants

GM crops may be inect-or herbicide-resistant and usually have increased yields

Advantages:
-Cloning can produce herds of cows with useful characteristics

-ACC may be used to make copies of the best animals e.g race horses

-If a person has a faulty gene they may have genetic disorder, if correct gene is transfered they may be cured

-Several medical drugs have been produced by genetic engineering such as insulin and antibodies

-GM crops include ones which are resistant to herbicides or to insects

Disadvantages:

-GM crops have a bigger yield, but farmers have to buy new GM seed every year because the crops are infertile

-Some people are concerned about accidently introducing genes into wild flower populations

-Insects which are not pests may be affected by GM crops

-Many people worry about eating GM crops and effect on the health

-Many people argue about whether or not cloning and genetic engineering are ethical.

Scientists have estimated that life began on earth 3 Billion years ago

Before the 18th century there were a few ideas about how evolution works
Lamark suggested a theory called "the interitance of aquired characteristics" Lamarks theory stated that characteristics which develop during an organisms lifetime can be passed onto the next generation. People found this difficult to believe. For example if two parents would go to the gym and their muscles were built in the gym, Lamarck believed that this would be passed onto the offspring.

Darwin suggested the theory of 'natural selection' after he had made a journey to the Galapagos islands. He recored many observations about life on the islands.

Darwins theory stated that small changes took place in organisms took place over a very long time. All organisms in a species vary and therefore some are more likely to survive (natural selection). Those that are best adapted breed and pass on their characteristics.

Darwin did not know about the genes. We can now say that the best adapted organisms survive to breed. They are the ones that pass their genes on to next generation. 

Darwins theory was gradually accepted for several reasons:

- The theory of natural selection challenged the idea that God made all the animals and plants that are live on Earth.

-Many scientists were not convinced because they still did not think there was sufficient evidence for the theory 

- Darwin could not explain why there was a variety in organisms or how inheritance worked. Scientists did not know about genes and genetics until about 50 years later

- Darwin had tried to show that birds, such as finches on the Galapagos islands could change over time if they lived under different conditions but he could not explain in terms of genes

Individual organisms will show a wide range of variation because of difference in their genes

All the organsims in the population will compete for food, shelter and mates

The organisms with characteristics most suited to enviroment will survive, e.g best camoflauge

The organisms which survive are more likely to breed succesfully 

The genes that have enabled these organsisms to survive are then passed onto their offspring

Sometime a gene accidently changes and becomes a new form of the gene. These changes are called mutations. If the mutated gene controls a characteristic which makes the organsim better adapted to the enviroment then it will be passed on to the offspring.

Mutations may be particularly important in natural selection if the enviroment changes. 

Grouping organisms is called classification

Biologists study the similarities and differences between organisms in order to classify them, The system used is called the natural classification system.

The easiest system to understand is one which starts with large groups and splits this up gradually into smaller ones. Thir largest groups are called Kingdoms.

The main kingdoms are:
-Plant kingdoms
-Animal kingdoms 
-The kingdoms which contain microorganisms

The smallest group in the classification system is the species

Members of a species are very similar and can breed together to produce an offspring