Genetics for beginners!
Genetics for beginners
I hope you appreciate this light hearted look at genetics which is a subject that is becoming more and more important in the field of assisted reproduction.
Written to help you understand various techniques which are now available to most IVF centres to compat infertility…..and answer the painful question Why didn’t I become pregnant.
From this page you may read with more authority the pages in kosmogonia that concern genetics.
Chromosomes, cell division and sex
All living things consists of cells that come in all shapes and sizes The human body contains trillions of cells while other more primitive creatures consist only of just one.
Scientist saw that all cells come from cell division of a pre-existing cell.
The early microscopes saw that just before cell division everything in the cell is doubled.
As microscopes improved the cell structure emerged..all cells had a nucleus and just before celldivision short stringy objects appeared, doubled and disappeared again. These where called Chromosomes.
This process was called mitosis.
The process of cell division ensures every daughter cell gets a perfect copy of chromosomes. The number of chromosomes will be the same in each cell.
Each species has a characteristic chromosome number
It was discovered in 1902 that each chromosome exists in 2 copies* (these are called homologous pairs).
This was the genetic material inherited from both our parents, one of each pair coming from ma and pa.
**It was noticed that one pair were not alike, one pair were similar but one of the chromosomes was shorter… this was found to determine the sex.
So one was called X and the shorter one Y. Humans for example have 46 chromosomes in total..22 homologous pairs and one pair determinig the sex…XX was female…XY was male.
The Y chromosome carried the transferable information for maleness!
Sperm and oocytes are single cells with only half of the Chromosomes..due to a process of double division called meiosis
At fertilization their nuclei unite giving the fertilized egg a full complement of chromosomes-half from the father and half from the mother
The DNA is the cells secret code that sends a message. It is copied when a cell divides and each cell in the human or any living organism contains the same genetic code.
Like any code it can be misread, copied wrongly or be missing vital pieces of information. The code can be used too many times a the message it has to say be misused or useless.
This code was unbreakable a few decades ago but now we are learning to understand it, use it to are advantage
Genetic engineering:
Genetic engineering is just that…..engineering.
The genetic engineer can cut, stick, splice (hybridize) and repair bits of dna.
Genes have on and off switches* too that can be turned on and off
In the genetic engineer’s tool bag he has enzymes (active proteins) taken from nature that can cut dna in specific places.
*the insulin gene is turned on in the panceas helping digestion of sugar but it is of no use in the a skin cell and therefore turned off there.
This turning on and off of genes especially interests us reproductive biologists who study the development of the embryo..but I’m getting off the point!
The over production of one protein can be harmful (like an overflowing sink) and unless turned off can cause disaster.
The little mistakes in reproducing the DNA code is called a mutation (a variation) and can be harmless with no great effects or harmful with severe effects.
According to how important the gene is, and how the variation effects the working of the cell determines it’s ability for the variation to exist in the cell and remain in the population (gene pool)..offsping.
The gene that makes eye colour has no great effect on the health of the individual and many variations are found.
The haemoglobin genes has several variations cause by mutation, some with little concequence and some severe like Beta Thalassaemia or Haemaphilia.
There is a gene that is so important to the cells survival that it has not changed in millions of year of evolution** and the exact same copy (DNA code) can be found in the human a cow and a Pea plant!
Genetic diagnosis
Using the genetic tool kit we can discover many things about the genetic profile of a genetic disease.
We found out information about genes many times when it is not doing what it is supposed to do!
If there is variation in the normal generic code we can read the code and a diagnosis is made.
The relationship between what the mutation actually does can still be unclear but we are collating data all the time.
Large pieces of DNA can be labeled with dyes that can be seen under the microscope..this helps us look for numerical problems. This is called cyto-genetics and the process is called F.I.S.H
We can see the absence of a chromosome, An extra chromosome e.g Downs, Or just to find to found out the sex of the individual….
If we dye the X chromosome green and the Y chromosome purple we can determine the sex ....one purple, one green = boy, two green = girl.
Enzymes exist in nature that attact DNA (such as a defence mechanism for many bacteria) and these Molecular scissors cut the enemies DNA into pieces.
Dna can be cut at specific places ( specific code sequences) and if you know the length of the normal piece of DNA …a diagnosis can be made by examining the aftermath of the dna-cutting lunch.
This is called molecular genetics…you can not see the DNA under the microscope but if you look at large amounts of dna strains through a filter.
Either by size or shape…differences in dna length can be found if the code has been changed.
A bit like sorting out spaghetti of different length
Since Dna is negatively charged and is attracted to a positive pole…the shorter pieces of dna move faster through the filter than the larger ones so by staining the DNA after the race the length of DNA can be determined.
This is called Electrophoresis
We use this technique in Pre-implantation Genetic Diagnosis for such diseases as Cystic Fibrosis or Beta Thalassemia.
PCR (Polymerase Chain Reaction)
In forensic science or for genetic diagnosis the amount of DNA can be so low it is impossible to detect by the above method alone.
He uses PCR.
The genetic engineer highjacks an enzyme found in nature use for DNA replication, and adding this to the soup of DNA constituants and the original sample DNA begins to replicate the DNA to detectable levels.
The theory of Gene Therapy:
Gene therapy to us is the manipulation of genes to allow a non functioning gene to work properly.
[Or for a gene to work in a cell that it was not intended…such as a cow to produce human insulin as well as the other nutrients in milk ..or a tomato to be fortified with a pesticide].
For example if one of the genes for making haemoglobin is damaged/mutated or missing, the insertion into the DNA of a normal working gene will remedy the problem and start to produce normal haemoglobin.
Stealing the mechanism that a virus uses to embed in DNA to reproduce, the genetic engineer hopes to jump-start the cells operations like replacing a spare part on a car.
Of course it is never that easy and there are several problems…the insertion of genes is often hit or miss and may insert in a site of another gene rendering both genes useless…or upside down making the code nonsense.. or insert in a remote area of the dna strand never to be read.
Hopes for the future are to use gene therapy to cure many single gene disorders either by transforming the cells within the body or by grafting skin tissue with altered DNA to produce the missing element that causes the disease.
Genetic counseling is the process by which patients or relatives, at risk of an inherited disorder, are advised of the consequences and nature of the disorder, the probability of developing or transmitting it, and the options open to them in management and family planning in order to prevent or avoid or it.
If seeking help with a fertility problem, you are faced with a genetic problem a genetic councellor is as important as your gynaecologist or embryologist in explaining and assisting in your fertility treatment.
