The best way to explain Genetics, is to start off small and expand out.
DNA is made up of 4 bases, Adenine, Thymine, Guanine and Cytosine. These bases are called, Nucleotides.
To the left is a basic structure of a nucleotide. The only thing different between A, T, C and G is the Base.
DNA
These Nucleotides are joined together, to form DNA.
Notice in the image to the right, there is a base pairing rule. A can only pair with T, and C can only pair with G.
These bases are held together by weak chemical bonds, meaning they can easily be broken and re-formed.
When we read DNA, each 3 nucleotides are refereed to as a triplet. Essentially, imagine your reading a book, and each word is only 3 letters long.
As we continue zooming out, we notice that a sequence of nucleotides is called a gene. A gene is just a segment of DNA, which codes for a protein.
Eventually, all these genes are tightly compressed and packaged into structures called Chromosomes.
Within your chromosomes you have roughly 30,000 genes. If we lay out all the DNA in just one cell, it would be over a meter long. This means they have to be extremely tightly packed around Histones (proteins).
In your body there are over 10,000,000,000 cells.
In humans we have 46 chromosomes or 23 pairs. This means half is from your mother (egg cell) and the other half is from your father (sperm cell).
As we continue back, we get to the genome. Every single gene in your cell, makes up the genome.
Eventually, we find all this information in the Nucleus. The storage centre for DNA.
The nucleus has tiny pores though out its membrane, allowing nucleic acids to leave.
Questions
1. Draw a nucleotide and circle the area which changes depending on the nucleotide. (4 marks)
2. What is the base pairing rule (2 marks)
3. What is the complementary strand to the following sequences (2 marks)
a. A T G G G C C T G A C G A
b. A A A A C T C G T G T A G
4. Define a gene (2 marks)
5. How is DNA packaged in the nucleus (2 marks)
As a detective you enter a crime scene. You notice there is blood splatter on the floor. On closer inspection you notice there is some dead skin cells left at the scene. You speak to the wife at the murder scene and find out that her husband is missing and possibly dead. After talking to her you find out they recently adopted a child as he was infertile.
Once you take both samples back to the lab you realise that they have three different Karyotypes.
This means they are from 3 different people. You deduce that 1 must be the victim, 1 must be the wife and 1 from the murderer.
6. Using your knowledge of chromosomal genetic disorders and karyograms, who do you suspect the murder, victim and wife to be and why? (5 marks)
