1. From Mendel to DNA Learning Objectives
What did Mendel’s experiments teach us about inheritance?
What are DNA fingerprints?
How are specific proteins made in the body?

2. Gregor Mendel Carried out breeding experiments with peas.
Used pure strains of: round, wrinkled, green and yellow peas.
Cross bred the peas and counted the different offspring.
Found that characteristics were inherited in clear predictable patterns.
Gregor Mendel was born in 1822 in Brunn Czechoslovakia. He was a very clever man but very poor so he became a monk to get an education. He worked in the monastery gardens and became fascinated by the peas growing there. He decided to carry out breeding experiments, using pure strains of round peas, wrinkled peas, green peas and yellow peas for his work. Mendel cross bred the peas and counted the different offspring carefully. He found that characteristics were inherited in clear and predictable patterns.
Mendel explained his results by suggesting there were separate units of inherited material. He realised some characteristics were dominant over others and that they never mixed together.
Gregor Mendel

3. Mendel kept records of everything he did and analysed his results
Mendel kept records of everything he did and analysed his results. In 1866 when Mendel was 44 he published his findings. He never saw or heard of chromosomes and never heard of genes. Yet he explained some of the basic laws of genetics in a way we still use today. Sadly Mendel’s intelligence was ahead of its time. As no-one knew about genes or chromosomes, people simply didn’t understand his theories. Died twenty years later – his ideas were still being ignored.
16years after his death his work was recognised. By 1900 people had seen chromosomes through a microscope. Three scientists discovered Mendel’s papers and repeated his experiments. When they published their results they gave Mendel credit for what they observed.
Ask students to draw the structure of DNA (AfL) and label it.
Mendel suggested that there were separate units of inherited material. He realised some characteristics were dominant over others and that they never mixed together.

4. Inheritance - the story of life
The work of Gregor Mendel was just the beginning of our understanding of inheritance. Today we know that our features are inherited on genes carried on our chromosomes. We also know what chromosomes are made of.
Your chromosomes are made up of long molecules of a chemical known as DNA (deoxyribose nucleic acid). Your genes are small sections of DNA. The DNA carries instructions to make the proteins which form most of your cell structures. These proteins also include the enzymes which control your cell chemistry.

5. A gene is a section of DNA coding for a particular feature.
Genes
A gene is a section of DNA coding for a particular feature.
e.g. eye colour, attached/unattached ear lobes, ability to roll tongue.

6. DNA is a chemical that stores your genetic material.
So what is DNA....
In April 1953 James Watson and Francis Crick presented the structure of the DNA double helix, the molecule that carries information from one generation to another. Firstly a triple helix was proposed (1951) – the theory was wrong (Watson and Crick worked on this theory). It was a photograph taken by Rosalind Franklin using X-ray taken using crystallographic methods, that revealed the double helix structure. Watson and Crick were awarded the Nobel Peace Prize, Rosalind Franklin was not. The Nobel Peace Prize can only be awarded to living people.
DNA is a chemical that stores your genetic material.

7. DNA
DNA = deoxyribonucleic acid (huge molecule). Each cell contains over 2 metres of DNA, coiled inside the nucleus. Your DNA contains all of the information needed to make you. Your DNA is different from another person’s DNA (unless you are an identical twin.
Genes make up chromosomes, genes are made up of DNA.
DNA is a double helix shaped molecule – it is a bit like a ladder that has been twisted into the same shape as a spiral staircase. The “steps” of the ladder hold together the two long strands – it is these steps that carry all the information stored in the DNA molecule.

8. Structure of DNA DNA Structure
DNA molecules are made of thousands of smaller units called nucleotides. Each nucleotide consists of three parts:
A phosphate
A sugar
A base
The sugar and the phosphate group join together and make the ‘backbone’ of each strand of DNA. The bases are bonded to the sugar group, they are also joined to a base on the other strand of the DNA, using a weak bond called a hydrogen bond. Although the bonds are weak, there are thousands of them holding the two strands of DNA together.
There are 4 bases in DNA:
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
The bases always pair up in the same way: adenine to thymine and cytosine to guanine.
Structure of DNA

9. Sequence of bases forms the genetic code
Each base is like one letter in a four-letter alphabet.
These letters make up 3 letter groups called codon triplets.
Each triplet is one piece of information. G C T A
The bases are grouped into threes and each group of three such as that on this slide codes for a particular amino acid. Each gene is made up of hundreds and thousands of these bases. The order of the bases controls the order in which the amino acids are put together so that they make a particular protein for use in your body cells. Each gene codes for a particular combination of amino acids which make a specific protein.
A change or a mutation in a single group of bases can be enough to change or disrupt the whole protein structure and the way it works. G C

10. Questions
How did Mendel’s experiments with peas convince him that there were distinct ‘units of inheritance’ which were not blended together in offspring?
Why didn’t people accept his ideas?
The development of the microscope played an important part in helping to convince people that Mendel was right. How?
Explain with reference to the structure of DNA the saying ‘One gene, one protein’.

11. DNA fingerprinting
‘DNA fingerprinting’ – a technique that uses the unique patterns in your DNA to identify you.
Your DNA is unique to you (unless you have an identical twin).
Other members of your family will have strong similarities in their DNA, but each individual has their own unique blueprint. Only identical twins have identical DNA.

12. DNA fingerprinting
Certain areas of your DNA produces very variable patterns under the microscope.
These patterns are more similar between people who are related than between total strangers.
The patterns are known as DNA fingerprints.
They can be produced from very tiny samples of DNA from body fluids such as blood, saliva, semen.
The likelihood of two identical samples coming from different people apart from identical twins is millions to one. As a result DNA fingerprinting is very useful for solving crimes. It is also used to show who is the father of a child when there is doubt.

13. Gel electrophoresis
Gel electrophoresis is a technique that uses electricity to move DNA through a gel to separate DNA fragments by size. Because DNA is negatively charged, it will be drawn toward positive charge. By placing a positive charge at the bottom of the gel, the DNA will be pulled through the gel towards the bottom. But, not all the DNA fragments will be able to reach the bottom of the gel because the gel is like a screen or colander through which smaller molecules can move easily. Larger DNA fragments will get stuck near the top of the gel, but smaller molecules will travel farther towards the positive charge. For example, in figure 2, we saw that person A had two small DNA fragments and person one had one fragment, after we treated their DNA with EcoRI. If we looked at their DNA using gel electrophoresis, we would expect to see two fragments in person A near the bottom of the gel and one in person B near the top of the gel (figure 3).

14. DNA fingerprinting – what are some of the uses?

15. Questions Two men claim to be the father of the same child.
Explain how DNA fingerprinting could be used to find out which one is the real father.

16. Inheritance in Action Learning Objectives
How is sex determined in humans?
Can you predict what features a child might inherit?
Remind students of the term genotype and phenotype

17. We inherit characteristics from our parents....
Nucleus
chromosome
gene
DNA

18. Humans have 46 chromosomes – 23 from the mother and 23 from the father.

19. The complexity of an organism does not seem to be correlated with the number of chromosomes it has.
Fruit fly – 8
Kangaroo – 12
Human – 46
Chicken – 78
Fern

20. In 22 cases each chromosome in the pair is a similar shape and has genes carrying information about the same things. But one pair of chromosomes may be different – these are the sex chromosomes.
Here is a set of a person’s chromosomes laid out and numbered. Up to now I haven’t told the whole story: these all go nicely into matching pairs (corresponding books from the two sets) except, in men, for one odd pair, as shown here. In men, these two are called an X and a Y chromosome, and their chapters (genes) do not correspond. They are two very different books. These do not get reshuffled, but instead one or other is passed on whole to the offspring. In women, these two are both X chromosomes, and their chapters (genes) do correspond. These do get reshuffled, and as with the other chromosomes, one new version is passed on which is a mixture of the two.
The father’s sperm determines whether the offspring will be a boy or a girl, since the mother will pass on an X chromosome but the father can either pass on his X or his Y. If it’s the X, he will have a daughter, and if it’s the Y he will have a son.
set of chromosomes can be separated from its cell, spread out on a microscope slide and magnified many thousands of times. When stained and photographed, they look like this:

21. Chromosomes from a female Chromosomes from a male
Human body cells each contain 23 pairs of chromosomes.
Parents pass on their genes to their offspring in their sex cells.
female sex cells are called egg cells, or ova
male sex cells are called sperm
A pair of chromosomes carry the same genes, in the same place, on the chromosome. However, there are different versions of a gene called alleles. These alleles may be the same on each pair of chromosomes, or different, for example, blue eyes or brown eyes.
Sex cells only contain one chromosome from each pair. When an egg cell and sperm cell join together, the fertilised egg cell contains 23 pairs of chromosomes. One chromosome in each pair comes from the mother, the other from the father.
Which chromosome we get from each pair is completely random. This means different children in the same family will each get a different combination. This is why children in the same family look a little like each other and a little like each parent, but are not identical to them.
Chromosomes from a female
Chromosomes from a male

22. Pair 23 – the non-matching pair of chromosomes
Sex chromosomes
Two X chromosomes mean you are female
One X chromosome and a Y chromosome mean you are male.
Twins are born. Twin A is XY and twin B is XX. What sex are the two babies?
Sex determination game

23. Chromosomes
The chromosomes we inherit carry our genetic information in the form of genes. A gene can be pictured as a position on a chromosome.
Many of these genes have different forms.
A gene can be pictured as a position on a chromosome.

24. Alleles – are different versions of the same gene.
For example the gene for dimples may have the dimple or no-dimple allele.
An allele can be dominant or recessive.
Individuals can be homozygous or heterozygous.
Individuals who are homozygous for a certain gene carry two copies of the same allele.
Individuals who are heterozygous for a certain gene carry two different alleles.
Alleles are different versions of the same gene. An allele can be dominant or recessive. Individuals, meanwhile, can be homozygous or heterozygous:
individuals who are homozygous for a certain gene carry two copies of the same allele
individuals who are heterozygous for a certain gene carry two different alleles
A recessive characteristic will only be shown if an individual is homozygous for the recessive allele. A dominant characteristic will be shown even if an individual is heterozygous for the dominant allele. e.

25. A recessive characteristic will only be shown if an individual is homozygous for the recessive allele.
A dominant characteristic will be shown even if an individual is heterozygous for the dominant allele.
Draw up diagram out of textbook.

26. Genetic diagrams are used to show possible outcomes of a particular cross. Dominant allele is shown by a capital letter, and a recessive allele by a lower case letter.
When genes from parents are combined, it is called a genetic cross. We can show this using a genetic diagram. A genetic diagram shows us the alleles for a characteristic carried by the parents, the possible gametes that can be formed from these and how these could combine to form the characteristic in their offspring.
When looking at the possibility of inheriting genetic diseases, it is important to remember that every time an egg and a sperm meet it is down to chance which alleles combine. So if two parents who both carry the cystic fibrosis allele have four children, there is a 25% chance that a child might have the disease. But in fact all four of the children could have cystic fibrosis, or none of them might be affected. They might all be carriers, or none of them may inherit the faulty alleles at all. Its all down to chance.
Carry out some punnett squares – write up on the board different examples, studetns are then to carry out the punnett squares and to explain them in words.

27. Tetanus Huntington’s disease Measles Malaria Haemophilia Meningitis
Organise the diseases into two categories
Downs syndrome
Cystic fibrosis

28. It is difficult to know whether a particular disease is inherited or not. The only way to find out is to carry out a pedigree analysis and go through the generations if possible.
Plenary – play the inheritance game.
Homework – research huntington’s disease and cystic fibrosis
Extension – sex-linked genetic diseases haemophilia and colour blindness
Inherited or not?