DNA and Genetics

L.O  To learn how DNA is present in humans and how that reproduction occurs in humans. Learn about why variation occurs in organisms.

Organisms of the same species will have many differences. This is known as variation. Variation simply occurs due to the different genes we possess. There are two different types of variation, environmental and genetic.


Genetic variation

Genetic variation occurs due to the different genes we get from our parents. The genes we get from parents are due to random chance so no two offspring will be the same, unless you are a twin!!!

In humans we get half of our genetic information for our mother and half from our father, that is why we look like our parents

The characteristics that are determined by genetics are characteristics such as eye colour, height, blood group


Environmental variation

Environmental variation occurs due to the differences in the environment we live in. The characteristics influenced by the environment are weight or sometimes even height.

Both determine the majority of your characteristics. A prime example of this is height as this can be determined by your nutrition but also can be determined by genes.


Genes, chromosomes and DNA

In the majority of cells we have a nucleus, within this nucleus we have chromosomes are contain our DNA

In humans we have 23 pairs of chromosomes, one chromosome from each parent. And these chromosomes contain the genetic information on the DNA





The DNA double helix is coiled up to form the arms of the chromosome. A gene is small part of a chromosome ,and therefore a small amount of DNA.

There can be different versions of the same gene, these are called alleles. For example for the eye colour gene you can have two different versions, consisting of two different colours.


Sexual reproduction

In sexual reproduction you will always produce genetically different cells.

Sexual reproduction combines a sex cell from the mother and the father. These sex cells are referred to as gametes.

Each gamete only contains 23 chromosomes, which is half a set within humans when these gametes fuse together they will from a full set of 23 pairs of chromosome.


Asexual reproduction

Asexual reproduction produces genetically identical cells. This is because is only involves one parent cell. There is no joining or mixing from two parents.

Within the parent cell there are chromosomes, which are made up of two identical halves. The parent cell will split into to two cells and in each cell will have one half of each chromosome.
Those chromosomes will then replicate to form full pairs and thus creating identical cells to the parent cell.

This method of reproduction is how all plant and animal cells replace lost or dead cells. Whereas bacteria will use this method of reproduction to produce offspring which is why they can reproduce at a quicker rate.



Cloning has been used in animals and plants.

In plants it is a more common method to regrow and reproduce many plants. One of the methods is called cuttings.

Cuttings involve taking a cut piece from a plant and replanting it elsewhere which will genetically reproduce the parent plant.
Another method is tissue culture; this involves taking a few plant cells and allowing them to grow in a growth medium with hormones. This allows them to grow very quickly in a short space.

Animals can also be cloned using a variety of methods. Farmers use the method of getting a sperm cell from the prized bull and an egg cell from the cow. Once these two cells fuse together an from an cluster of cells, they are then separated forming clone cells. These cells are then implanted in other cows until they are ready to give birth. This method is known as embryo transplants.

Another method is adult cell cloning in which an adult egg cell is taken and the nucleus is removed. The nucleus from another adult cell is then taken and added to that egg cell. The egg cell complete with a new set of DNA is then given an electric shock to allow it to divide.

Once the embryo has reached a ball of cells it is then implanted into a female until it gives birth to an identical copy of the adult cell.


This diagram illustrates this


Problems with cloning

Cloning, although it is a quicker way of producing offspring I will reduce the gene pool, making that set of offspring susceptible to disease

• Studies of cloning done in the past has shown that especially in adult cell cloning the new born clone often has an old set of genes and will therefore show signs of ageing very quickly

• Many people are worried human may be cloned which bring about many issues


Genetic engineering

Genetic engineering is the concept of being able to use enzymes to “cut and paste” genes from one organism to the next.

A key example of this is the use of insulin. In type 1 diabetes some people cannot produce effective insulin. So therefore insulin can be taken from a healthy insulin cells.

They can then be transferred to bacteria, which reproduce quickly and can be used to form drugs.


Human DNA


Genes can also be transferred into plants. In plants it is also very important as it can be used to make plants resistant to certain pests or viruses to ensure that farmers have a  higher yield.Advantages and disadvantages of genetic engineering

Advantages and disadvantages of genetic engineering



  • GM crops will help to increase the yield as more plants are likely to survive
  • People in developing nations will be able to get more food as plants can be engineered to have more nutrients



  • GM crops will reduce the biodiversity as it will reduce the number of weeds growing
  • Some people are worried that GM crops may not be safe
  • There are concerns that the genes for resistance that are in the plants may get transferred to other pests and weeds




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