B1 Genetic disorders

What is a genetic disorder? Well, basically it's a disease caused by faulty alleles. Remember, alleles are the 2 different forms of the genes so if these are altered then the genotype and phenotype could be altered. This is not important if it means that you can't roll your tongue or you haven't got an ear-lobe! It is important if you end up with sickle cell disease or cystic fibrosis.

Let's work out how you can get these disorders, no, I am not going to call it a disease 'cos you can't catch it like a bacteria, fungus or virus. You don't get it from someone sneezing! You get these disorders from faulty alleles passed down to you from your parents. Remember though, it is all down to probability. It's the chance that someone has of getting the disorder from their parents alleles.

So, what is the chance? Well, sickle cell disorder and cystic fibrosis are both caused by faulty alleles which are recessive. This means that you have to get 2 copies of the recessive allele to get the disorder. You have to get one copy of the allele from your mum and one copy for the allele from your dad. As it's recessive, if you only get one copy of the allele then the other would be dominant therefore you wouldn't get the disorder. You would however still carry the recessive allele so you would be a carrier.

Sickle cell disorder

Sickle cells results in the red blood cell being a sickle shape - these are the pink banana shaped cells in the photograph. The sickle cell is caused by a mutation in the haemoglobin. Haemoglobin is the pigment in the red blood cell that carries Oxygen so these mutated cells can carry less oxygen that the normal red blood cells which are bi-concave shaped. The sickle cells are also not as flexible as normal red blood cells so sometimes get stuck in blood vessels.

Symptoms of sickle cell
People with these disease easily become tired and short of breath because they cannot carry enough oxygen around their body for respiration.

They also have at times very painful joints because the sickle cells have stuck together and blocked some blood vessels - this could be fatal!

Cystic fibrosis symptoms

This is another disorder caused by a recessive allele. Remember you must get 2 recessive alleles to get this disease - just like Sickle Cell disease. So it's people who have 2 copies of these diseases who suffer from it.

In cystic fibrosis the lungs get clogged up with thick mucus. This makes it difficult to breathe. The mucus also traps pathogens which leads to infections. This thick mucus will also block some of the tubes that carry enzymes to the small intestine. Remember, enzymes break down large molecules in food into smaller molecules. Example, proteins are broken down into amino acids. If you are not absorbing enough nutrients then you will not put on weight.

Family pedigree charts

Doctors create pedigree charts like the one above to show how a genetic disorder is inherited and to show how the disease is passed on through the family. They can then work out the chances, the probability that a person may inherit this disease. This is called a Pedigree analysis. They could also inform parents of the probability of them passing on the disease to future children. This would help them decide if they want to have babies or not. What a horrible decision to have to make eh?!

B1 Explaining inheritance - Punnett squares

Punnett squares are also called Genetic diagrams. Useful for showing the probability of organism getting a certain allele. Who cares - you might say. Well it is useful not only for plant breeders but for working out the probability of someone giving birth to a baby with a genetic disease like sickle cell disease or cystic fibrosis.

Look at the example of the flowers Both parent flowers have the same phenotype and genotype. Thet are both phenotype purple and genotype Bb.

Notice, that one of the flowers is white. That is because it has received one recessive white allele from the pollen and one recessive white allele from the egg.

This gives it a probability of 1/4 = 0.25 being white or 0.25 X 100 = 25%

B1 Explaining inheritance

It all started a long, long time ago.

An Austrian monk in 1865 called Gregor Mendel put forward his ideas on genes and alleles. He did all his research on pea plants and actually grew over 29,000 plants!

Back to the beginning - again!

Plants and animals produce sex cells, these sex cells are called gametes. The male gametes in animals are called sperm cells and in plants they are called pollen grains. The female gametes in both plants and animals are called egg cells.

A huge difference between sex cells and body cells ( body cells are all the other cells) is that the sex cells have only one copy of each chromosome and therefore only one allele for each gene.

But why have they only got one copy - well let's think about human beings. All our body cells have 23 pairs of chromosomes which is 46 chromosomes. Remember, we get 1/2 our chromosomes from mum and 1/2 from dad. So, if the sperm has 23 chromosomes and this joins or fuses with an egg cell which also has 23 chromosomes then the fertilised egg or zygote now has 46 chromosomes or 23 pairs.

23 + 23 = 46 obviously!

Now, there are a lot of fancy words to learn and understand here - but once you get them it is all really easy - honest. Let's go back to genes. Each gene has 2 alleles. Now, imagine that a flower can be one of 2 colours - red or white. If a pure bred red flower gives its pollen to fertilise the eggs of a pure bred white flower then the flowers grown from the seeds are always red. This is because the flower receives 2 alleles for flower colour - one for red and one for white. The white flower allele has no effect if the red colour allele is also there. The red colour in this case is said to be dominant and the white colour is said to be recessive. The white colour for this flower can only happen if it gets the recessive alleles for white form both parents.

When,drawing diagrams to predict what will happen we use letters to represent the alleles. A capital letter is always used to represent the dominant allele and a small letter for the recessive one. In this example let's use R for the dominant red colour and r for the recessive white. Oh, and don't forget, the alleles are in pairs so the pair of alleles a flower could have would be, RR, rR, Rr or rr. Rr and rR are classes as the same.

RR must be red as it only has the red alleles.

Rr also must be red because even though it has the white r allele, this is masked by the dominant R allele.

rr must be white because it only has the white allele.

Time for some more fancy words here.

The alleles in any organism make up its genetic makeup and so is called the genotype.

What the organism looks like is called the phenotype.

So, RR is the genotype and the phenotype is of a red flower.

and, Rr is the genotype and it the phenotype is also of a red flower - (R is dominant to r).

rr is the genotype and the phenotype is of a white flower (there are only r alleles)

Notice the different genotypes that can produce the same phenotype.

If both alleles are the same, like RR or rr, then the organism is homozygous.

If both the alleles are different, like Rr, then the organism is heterozygous.

B1 Genes

Jeans for genes sounds familiar. This is where you wear jeans to raise money for research into genes.  But what are genes, where are they found and what to they do?

Well, lets start at the very beginning, let's zoom in on a cell.

First of all, you must be able to draw and label a plant and animal cell.

Inside the nucleus there are long strands of DNA. 

Each strand forms a chromosome.
Now chromosomes are divided up into genes.

So the chromosomes are found inside the nucleus. The nucleus contains different chromosomes and these are arranged in pairs. Humans have 23 pairs of chromosomes. Notice in the diagram below the chromosomes at the end are an X and a Y. This tells you that this is a male. If there were 2 X chromosomes it would be a female.

Different chromosomes contain different genes and each gene does a particular job. Eg. many of these genes control what we look like, hair and eye colour, ear lobes etc.

Variation caused by genes is called inherited variation - yes it's back to variation again! This is because we inherit our genes from our parents, 1/2 from mum and 1/2 from dad.

So genes carry the code or instructions for a certain characteristic. Some genes for the same characteristic may have 2 slightly different versions which give slightly different instructions to make differences and variations. These different forms of a gene are called alleles. There are different alleles for your eye colour eg. brown or blue.

Summarising all this then, there are 2 copies of each chromosome in the nucleus and there are 2 copies of every gene that makes up the chromosome called alleles.

Exam tip - if you are asked about characteristics and genetic then talk about alleles not just genes.

B1 Evolution

Evolution. I think that was the name of a film. I know it was, about life that starts as a single cell and quickly evolves to flying like dinosaurs. Well, I enjoyed it. Now, back to evolution.

Evolution means 'a gradual change over time'

The names Charles Darwin usually springs to mind. He lived from 1809 - 1882. Scientists then realised that species can change over time but didn't really know why. Darwin, took all the various ideas about what happened and with his own research and ideas and came up with his theory of Natural Selection. He published his theory in a book called On the Origin of Species by Means of Natural Selection. 

So, what's it all about then. Well, back to variety and variation. Let's think of a the ancestor of the giraffe. It didn't always have a long neck and was probably like a little deer. Now, a group of these animals would show some variation - they would all be slightly different. Maybe, some of them had a slightly longer necks than others. Can you see where this is going. Now, imagine that there is some sort of drought. The grasses die out but trees survive because they have longer roots. The giraffey things that have the slightly longer necks can reach the leaves on the trees and so they survive. The ones with the slighter shorter necks cannot and so  die. This means that the ones that survive can breed and pass on their characteristics - alleles - to their offspring. This is Survival of the fittest. Over a period of time the population will change to have loner necks. Any species that haven't adapted to an environmental change will die out and become extinct. 

It could also apply to predators. A lion has a litter of cubs. The strongest one has the best chance of surviving. Survival of the fittest.

Now, don't think that evolution is all to with animals in the past - you know, dinosaurs and all that. 

Evolution is happening all the time! Rats are now resistant to a poison called warfarin.Warfarin is a poison that stops the rats blood from coagulating. When it was first used most of the rats died, but some survived because of variation - they were slightly different. These survivors bred and now all the rats are resistant.

Darwin, when on his travels to the Galapagos Islands noticed that the finches, a type of bird, on the different islands all kind of looked the same but they all had slightly different beaks. He worked out that originally they were all one population of birds on one island. Maybe a storm or something blew them all onto different islands. As the birds were originally slightly different due to variation then maybe as the islands were all slightly different then different birds would survive and breed on different islands. There is a lot of differences there eh?! Over time, these survivors on each island would breed and eventually become so different that they couldn't interbreed with birds from other islands.

Survival of the fittest.

They had become a new species  - this is called speciation.

B1 Reasons for variety

Why are species all so different? Wouldn't it be easier if they were all the same? No it would not, it would also be extremely boring, scary even. Think if every species, even humans were exactly the same as each other.

Aaaahhhh!!!!!!!!

All organisms are adapted to their surroundings. They have all these variations so -  they can survive in whatever habitat that they are living in.

There are a few specific animals that you must know about.

1) Sharks. Don't just think of the obvious bits, like streamlined shape to move fast and catch their prey, or sharp teeth to catch and kill their prey. Shark tissues contain TMAO - ( this stands for trimethylamine N-oxide if you are interested - but you don't have to know it) Anyhow, TMAO is poisonous to humans in high concentrations - so don't go to your local chippie and ask for shark and chips please! But wait, why would a shark evolve to be poisonous to human beings? We didn't evolve to be a predator of sharks! Here's clue. Greenland sharks, found in the Arctic Ocean, which is pretty cold, OK very cold, contain much higher amounts of TMAO than other sharks. Why? It;s because TMAO happens to be a natural antifreeze and just happens to be poisonous to us by the way.

2) Polar bears. Yes, all right we all know its got white fur for camouflage and maybe the thick fur and blubber for insulation. You might even know already about it having large feet to spread out its weight - reduces the pressure on the snow and ice or even that it has got rough soles on its feet to grip the ice. But, did you know that it has small ears to reduce the heat loss? Did I mention the sharp teeth?

3) The final animal is the Pompeii worm. Yes, I admit it. It's not exactly a well known beastie is it - but it is a survivor and a great example of the variety of organisms. So, what's so special about this worm. Well, mainly it has adapted to live near deap-sea hydrothermal vents. Here, hot water at temperatures of more than 350 oC come out of the vents and cool quickly. This is at depths of over 2km where it completely dark with high pressures, over 200 times those at sea-level. This worm spends a lot of its time inside a papery tube to protect itself from predators. It is covered in a thick layer of bacteria, that helps protect it from the heat. It can also survive the great pressure. It also has no eyes 'cos it's so dark if it had it wouldn't be able to see anything anyway!

B1 Continuous or discontinuous variation

Not more variation - well only as wee bit more.

We can divide variation into two types.

Continuous variation or discontinuous variation.

I hope by now that we all now that there is a big amount of variation between the same species and between different species.

Continuous variation is where there is a complete range of differences example height. Humans are not either short or tall, they can be anything in between. There is a continuous range of heights. If you drew a graph of this it would be a normal distribution curve. Characteristics that show continuous variation are often controlled by both genes and the environment. Example, you may inherit the alleles that may make you tall but unless you have the correct balanced diet you might not. If you don't grow tall, but you could have then this is called an Acquired characteristic. Acquired characteristics are caused by the environment and so are cause environmental variation between organisms. Makes sense to me.

Discontinuous variation is where there is a definite fixed value. You are either one thing or another. Your blood group is an example of discontinuous variation. You are one of 4 groups, A, B, AB or O. That's it - you must be one of those 4 goups and not nearly one or have a bot of 2 or ........ . You could draw this as a barchart. Discontinuous variation is usually caused by changes in the DNA so it is called Genetic variation.

B1 Variation

What is variation? Differences in characteristics are called variation.

There is variation within a species but obviously much more variation between different species. Think of the variation between dogs which are the same species. There are lots but then think of the variation between a dog and an elephant - lots more differences. Yes, I know it's obvious and probably a stupid example but it makes the point - I hope!

Variation makes it hard to classify animals and plants and to decide if they are different species. So, how do they do it? Well, if someone finds what they think is a new species, that is not enough to actually say that it is a new species. Say I found a new bat - I think I will call it Batty glover. Note, the Genus is Batty and the species is glover. This one bat may be just a one off hybrid so I would have to find some more. Then I could see if these new bats were different enough from other bats but themselves pretty similar to be called a new species. Guess there will not be a Batty glover yet!

Finally, all this classification stuff. Variation, Kingdoms and all that - what is the point? Why bother?
Is this just something to keep scientists in a job? Well no it isn't - honest it isn't.

It is important to classify organisms using the binomial system because it allows biologists to:

1) easily identify new and existing species.

2) see how organisms are related.

3) identify areas of greater and lesser biodiversity.

Typical teacher - explaining it nicely and then throws in a big new word. What is biodiversity?

Biodiversity is a measure of the total number of different species in an area.

What has that got to do with anything? Well, it's really very important. We get lots and lots of many different and important products like food and medicines from living things. The more species there are, the more things we have to discover new products. That sounds pretty selfish, we are just identifying them so we can use them. Probably true but on the positive side if we need them then there is more chance that we will look after them and conserve them. Biodiverse areas are more likely to recover quicker from a natural disaster like flood, drought or fire than a less diverse area because there are more species that could survive and breed. Many biologists also think that as countries and governments only spend so much on conservation that if they can identify areas where there is a large biodiversity  - which they call a biodiversity hotspot - then governments could first of all concentrate on these areas because they could save a greater number of species. Pity we can't save them all though but it's down to time and money.

B1 Species

What is a species? Are you a species? Yes you are - you are a human being - I hope! Anyhow, what is a species? Well a species is defined as a group of organisms that can interbreed (that means reproduce with one another) to produce offspring that are fertile (able to reproduce).

Pretty straightforward eh?! Unfortunately Science is never quite a clear cut as that. Two closely related species can often breed and produce hybrids. An example of this would be a Zeedonk made from a Zebra and a Donkey. Hybrids are neither one species nor another and have characteristics of both parents. Problem is that they are usually infertile.

Makes sense really - well nearly. Remember, it is not just about animals. Many plants and fungi produce new offspring from parts of the adult. Think of spider plants with the 'baby spider plants' hanging off them. Each baby plant just has one parent! This is asexual reproduction.

Also, bacteria and many protoctists reproduce by just splitting in half - again there is only one parent.

So, basically, if there are 2 parents then you could get a hybrid - a lion and a tiger would make a Liger and if there is only one parent then interbreeding can't happen.

Did I mention ducks - no, but I will. Ducks, in particular Mallard ducks can hybridise with closely related duck species to produce fertile hybrid offspring. These hybrid offspring can then breed with other hybrids or other hybrid ducks so you end up with lots and lots of ducks with a continuous range of shapes and colours (different characteristics)  but they are actually the same species.

Sticking to the bird theme we have examples where you might have groups of the same species in a population may breed with a nearby similar population which is slightly different. This population might breed with a different closely related population to it and so on. Hold on a minute,  just read that last bit and it was as clear as mud. Lets think of it in a Maths way.

A  B  C  D  E  F  G

A can breed with B, B could interbreed with C, C could breed with D, etc, but A could not interbreed with G because they are too different. Sometimes this chain of inbreeding actually forms a ring where there is not end but species near each other can interbreed. These are called ring species. 

Sea gulls form ring species and because there is a gradual change between the characteristics of the gulls it is really hard to decide if there are different species or still hybrids. Aaahhhh!!!!!!!

B1 Classification

Now, what is this classification all about? Some folk get really mixed up about all this but don't worry. It really is quite easy and I'm not just saying that because I am a science teacher - honest.

So where do we start. Let's start at the very beginning  - I think there is a song there!. Basically, all living things are put into groups because they have things that are the same. They have similar characteristics.

To help scientists and people who study living things talk about the same thing we use a classification system to classify (organise) living things into similar groups. These 'fancy names' ensure that no matter what language you speak you can talk about the same organism.

Panthera tigris is a tiger. Panthera leo is a lion - think of Leo the lion or the zodiac sign of leo. Notice there are 2 words - this called the binomial system of  classification. Bi means 2 like in bicycle. Anyhow, you have got to know the order of the grouping system we use - so learn it OK.

Kingdom
Phylum
Class
Order
Family
Genus
species

If it helps to remember the order the just learn, King Phillip Came Over For Gooseberry soup.

So, with Leo the lion, Panthera is the Genus and leo is the species. The clue for the species is it is always the last word of the pair and it always starts with a small letter - Panthera leo.

 If you are still wondering why we bother with all this then think of the common woodlouse - Armadillidium vulgare. If I was giving a lesson on these wee beasties I would call it a 'slater' and you might not know what I was talking about so we use the binomial name so everyone everywhere who studies these crustaceans knows what is is.

The five kingdoms of organisms. Sounds impressive eh?! Kind of Lord of the Rings stuff.

B1 Vertebrates and invertebrates

Right now, let's get started.

Remember the five kingdoms? One of them was Animalia. Well, we can divide animals into 2 groups whether they have a backbone or not.

Animals that have a backbone, like us, are called vertebrates. All vertebrates belong to the phylum Chordata because they have a supporting rod that runs the length of their body. Does the phylum part ring a bell? Kingdom, Phylum, Class, Order, Family, Genus, species. Hopefully, it's getting easier as it all links together. So, we are vertebrates OK. Animals that don't have a backbone are called invertebrates.

Now, back to the vertebrates. These can be divided into 5 groups. The groups are:

Amphibians  Reptiles  Birds  Fish Mammals

Fish have gills to take Oxygen from water, so do young amphibians, like tadpoles. The other groups and adult amphibians have lungs. We are mammals so we have lungs.

We could also divide up the animals into how they reproduce whether it is external fertilisation or internal fertilisation. Also, many vertebrates lay eggs and they are called oviparous. 

Mammals like us give birth to live young - we are called viviparous.

Another way we could group and classify the vertebrates is by using their body temperature. Animals like us - we're mammals remember, keep our body temperature the same regardless what the environment temperature is. We are warm blooded but use the proper name which is homeothermic. Mammals and birds are both homeotherms. The other animals are cold blooded but you must use the word poikilothermic. Fish, reptiles and amphibians are all poikilotherms.

Just remember to use the fancy words and not just warm or cold blooded. A lizard is cold blooded but if it lies in the sun it will get warm blood - obviously. That's we  - and I mean by that you, must use the words homeothermic and poikilothermic.

B1 The five kingdoms of organisms

The five kingdoms of organisms. Sounds impressive eh?! Kind of Lord of the Rings stuff. It's not really too hard - just lots of facts to learn. It's more of classification and basically the reasons and characteristics to explain why we have these 5 kingdoms. Oh yes, the 5 kingdoms are:

1. Animalia
2. Plantae
3. Fungi
4. Protoctista
5. Prokaryote.

So you can take any living thing and put it into one of these 5 groups which are called kingdoms.

Now, lets think how we could divide all the living things into groups.

Some are unicellular - these have one cell and others are multicellular.
Many cells have a nucleus, like our cells but some like bacteria do not. Bacteria are members of the Prokaryotae group. You could also look at how the living thing gets its food. Some, like plants, make their food autotrophically using photosynthesis, while animals get their food by eating and digesting other living things heterotrophically. Fungi also get their food by digesting other organisms, but they do this outside the body and they are said to feed saprophytically.

So now we've got the basic differences between living things to put them into one of the 5 kindoms - hurrah! Here goes:

1. Animalia - multicellular, heterotrophic so no photosynthesis so no chlorophyll. Look in the mirror! You are not green - I hope. Complicated cells with a nucleus. 
2. Plantae - multicellular, autotrophic feeders. Photosynthesises using chlorophyll. Cell wall made of cellulose. Complicated cells with a nucleus.
3. Fungi - multicellular, cell wall is not made of cellulose. saprophytic feeders so no chlorophyll. Complicated cells with a nucleus.
4. Protoctista - Mostly unicellular. Complicated cell with a nucleus.
5. Prokaryote - Unicellular. Simple cell structure with no nucleus.

Learn the above because it comes up a lot in exams. Last little bit coming up. There is no kingdom for viruses because it is not classed as being alive.Yes, I know that viruses multiply inside a cell but it does not show any other life processes like growth or feeding so it is not alive.