In the news today, you always hear about cloning, genes and DNA. But do you know what these words mean? If you don't, then you are in the right place. This page will discuss DNA, genes, inheritance and cloning. Please note the page is written simply so that someone who has very basic understanding of biology will grasp the information here. READY? HERE WE GO!!
Above is a typical animal cell. The part we are interested in is the nucleus. The nucleus is the brain of the cell.
Instructions providing all the information necessary for a living organism to grow and function are present in the nucleus of every cell. These instruction tell the cell what role it will play in your body. e.g. They tell the cell it will make up part of your leg.
The instructions are in a form of a molecule called DNA (DNA stands for Deoxyribonucleic Acid). These molecules hold a detailed set of plans (like a blueprint) for building different pieces of the cell.
Genes are instruction manuals for our bodies. They are the directions for building all the proteins that make our bodies function. Specialised proteins put colour in your eyes, others work on the hairs inside your ears that help you hear!!
DNA is made up of genes. One DNA strand contains many genes. All these genes are needed to give instruction for how to make and operate all parts of our bodies. (See below)
Each cell in our bodies contains a lot of DNA. In fact, if our cells were enlarged to the size of an aspirin tablet, our DNA would be 10,000 metres long. That's the same as 109 Old Trafford football pitches. How does all this DNA fit in a cell?
DNA is packed into compact units called chromosomes. Chromosomes are efficient storage units for DNA. How many chromosomes does one cell hold? Almost all human cells have 46 chromosomes. All the DNA is organised into 2 pairs of 23 chromosomes. ( See below )
We get genetic materials from both our parents. That's why children look like both mum and dad. Look at the above set of chromosomes. You can see the matching chromosomes have been linked up in pairs. One from mum and the other from dad. There are two chromosomes that determine whether you will be born male or female. In the picture, the sex chromosomes are labelled X and Y. the chromosomes in this picture are from a male. You can tell because females don't have a Y chromosome. Instead, they have two X chromosomes.
Not All living creatures have 46 chromosomes like human beings. Mosquitoes have for instance 6, onions have 16. Carps (a fish) have 104!!
INHERITANCE:
"Like father like son"
"She's got her mother's eyes"
"A chip of the old block"
Why are we like our parents? Why do we look like our brothers and sisters? It's because of our genes. Each one of us receives traits from both mum and dad. the passing of genes from parent to child is called the basis of inheritance.
If we inherit our parents genes, why is it that we don't look exactly like them? Children aren't identical to their parents because each receives half their genes from their mothers and the other half from their fathers. This means each child has some of each parents traits but not all of them.
HOW DOES THIS HAPPEN?
In all of us, there are very special cells called reproductive cells namely sperms and eggs or "ova". Sex cells are unlike other cells in the human body. They have one set of chromosomes, while other cells of the body contains a pair. This makes the number of chromosomes in a sperm/egg 23!, while all other human cells have 46 chromosomes. When the sperm and egg come together, they combine both their 23 chromosomes making a cell with 46 chromosomes. As a result, each one of us started with two sets of genes. In the book of Genesis 2:24, God said "... two shall become one". In MY OWN OPINION, God was referring to the coming together of two 23 chromosome cells to make one 46 chromosome cell !! Read more here on inheritance
CLONING
Have you ever wished you could clone yourself to do something you don't want to? Imagine this was possible. Where would you start?
What is cloning?
Cloning is the creation of an organism that is an exact copy of another. This means every single bit of DNA is exactly the same between the two. You might not believe it, but there are human clones within our communities. No they weren't made in a lab, they're identical twins created naturally.
How is cloning done?
Did you hear recently in the news of the religious group claiming to have cloned babies around the world? Do you remember Dolly the sheep in 1997? How does one go about making an exact copy of an organism?
Somatic Cell Nucleus Transfer (SCNT) was the method used to create Dolly the sheep. Don't worry about the fancy words. We will look at each word and find it's meaning.
Somatic cell: A somatic cell is any cell in the body other than the reproductive cells i.e. eggs and sperms.
Nucleus: The nucleus is like the brain of the cell. it is an enclosed compartment that contain all the information the cell needs to form an organism.
Transfer: Moving an object.
To make Dolly the sheep, researchers isolated a somatic cell from an adult female sheep. Next, they removed the nucleus of an adult sheep's egg. Then, they transferred the nucleus from a somatic cell to the egg. Remember the egg naturally had 23 chromosomes. Now it had 46 chromosomes. This fooled the egg to think it was already fertilised and it started multiplying. It developed into an embryo which was implanted back to the surrogate mum. The egg continued growing until Dolly was born.
Why is cloning very controversial?
Cloned animals that do survive tend to be much bigger than their natural counterparts. Scientists call this "Large Offspring Syndrome" (LOS). Clones with LOS have abnormally large organs. This can lead to breathing, blood flow and other problems.
As cells divide, their chromosomes get shorter and shorter (the process of aging). the older you are, the shorter your chromosomes are. So what happens to the clone if the chromosomes transferred in the nucleus are pretty old? When scientists looked at this, they found no clear answers. Chromosomes from cows and mice seem to be longer. On the other hand, Dolly the sheep had shorter chromosomes than her natural counterparts.
Imagine going for a regular check up at the doctor's clinic. What if he could check your genes? He could find hidden signs that indicate you are susceptible to certain diseases. Now, imagine this information going into the wrong hands e.g. Insurance companies, employers etc. Discrimination could arise against people who have "unhealthy" genes!
Genetic Disorders
Genetic disorders are medical conditions caused by mutations (changing) in a gene or a set of genes. they can happen at any time, from when we are a single cell to when we are 90 or even older!
We can separate these in 3 categories:
Chromosome Abnormalities: In some disorders, the entire chromosome or large segments of them are missing, duplicated or otherwise altered. Down's syndrome is an example. In Down's syndrome, a person has 47 instead of 46 chromosomes.
Single Gene Disorder: Some disorders result when mutation causes the protein product of a gene to be altered or missing. An example of this is sickle cell anaemia. This genetic diseases affects the red blood cells of people with the condition.
Multifactorial Disorders: Multifactorial disorders result from mutations in multiple genes, often coupled with environmental causes. Cancer and Diabetes are examples of these.