Lesson video

This lesson is discontinuous variation; data handling and analysis from the unit, variation, differences within species.

Hi there, my name's Mrs. McCready, and I'm here to guide you through today's lesson.

So thank you very much for joining me, and I hope you're looking forward to today's lesson.

In our lesson today, we're going to plot some data on discontinuous variation using a bar chart, and we're gonna suggest some possible causes for this variation.

Now, we're gonna come across a number of keywords in today's lesson, and you can see them listed on the screen there.

You may wish to pause the video and make a note of them, but I will introduce them to you as we go throughout today's lesson.

So in our lesson today, we're going to first of all plot our discontinuous data before we go on to analyse it and draw some conclusions from it.

So I hope you're ready to get going.

Let's get started.

Thank you.

So we have seen that there is great variation between individuals within a species, and some of this variation is discontinuous.

This means that those features have a very limited number of specific possible variations.

For instance, earlobe attachment and the ability to roll your tongue or not are good examples of discontinuous variation.

Now, when we observe discontinuous variation, we get discreet data that is categorised into groups.

And that means that we can put an individual into a category or another, or maybe a third one for instance.

So let's consider this class's ability to roll their tongue.

We can see that seven students cannot roll their tongue at all.

14 of them can only roll their tongue into a straw.

And nine of them can pucker it up right at the very end into quite a convoluted shape.

So you can see that these are discreet data categories.

It is either you cannot roll your tongue at all, you can roll your tongue into a straw or you can pucker your tongue either or, or or.

There's no great variation in between this and there aren't many, many, many different categories.

Now, because of that, we can plot our data as a graph and that will help us to see trends and patterns much more easily.

Now, because discontinuous data falls into discreet categories with no in-between values, it means that we can plot our data as a bar chart.

Now, a bar chart displays data as distinct columns, which are of equal width, but do not touch each other as shown in the diagram.

You can see that the columns are all the same width, but they aren't touching each other, and they could in fact be organised in any order at all without having any impact on the data itself.

So this is a bar chart and this is how discontinuous data needs to be plotted.

So which of these graphs would be most suitable for plotting discontinuous data? The line graph, the histogram or the bar chart? I'll give you five seconds to decide.

Okay, did you choose the bar chart? Well done.

So we're going to plot a bar chart using some discontinuous data.

For instance, the ability to roll your tongue or not.

So let's see, how do we make a bar chart? Well, firstly, you need to start with the x-axis.

You'll need to assign a column for each category and add labels to each column and a label for the axis.

Make sure that the columns are all of the same width and that there is a space between each one of them.

Then once you've finished the x-axis, you can move onto the y-axis.

And that involves then you plotting the numbers for the frequency, the number of individuals for whom that feature is relevant in equally-spaced increments up the y-axis.

You can see that in the example graph there, the numbers going up in two, so 2, 4, 6, 8, 10, and they're equally spaced apart.

Then you'll need to label the axis, draw the columns to the correct height and shade or colour in the columns.

Then finally, add a title to the graph to complete it.

So which label will go on the x-axis? Will it be feature, number of individuals or class trend? What do you think? I'll give you five seconds to decide.

Okay, did you choose feature? I hope so.

Well done.

So you might have collected your own discontinuous data or you might not and need to use some data that I'm providing you, which is present on the additional worksheet.

Either or, get hold of the data that you're going to be using and then use graph paper to draw a graph to show that data.

Make sure your graph has labelled axes and appropriate scale, lines drawn straight with a ruler and pencil please and a title.

So pause the video and come back to me when you're ready.

Do take your time though.

Okay, hopefully your graph should look something like one of these examples, either with your earlobe attachment or your class trends in rolling tongues.

Do check that you have correctly labelled your axes and that the individual categories are labelled too.

That the numerical values on the y-axis go up in equal-sized increments such as 5, 10, 15, 20, or 2, 4, 6, 8.

That both axes are labelled and the graph has a title too.

Okay, well done because that's quite tricky.

What we're gonna do is have a look at our data and draw some conclusions from it.

So having a look at the graph on earlobe attachment, for instance, we could say that the majority of the class, that's 27 out of 30 students, have unattached earlobes and only three of them have attached earlobes.

Now that would be a fairly quick and concise summary of the data and your description, your explanation needs to fairly and without bias or distortion, summarise the data that you have collected.

So from the bar chart, which description do you think is most appropriate? Is it A, fewer than 10 people had blood groups B and AB? Is it B, the vast majority of people had blood group O? Or is it C, 3 people had blood groups B and AB and 9 out of 24 had blood group A? Which do you think is the fairest and least biassed? Okay, well, hopefully you've chosen the third option.

Three people had blood groups B and AB and 9 out of 24 had blood group A, well done.

So there are a number of factors that influence an organism's characteristics.

Genetics, environment, and lifestyle choices.

Now, discontinuous variation usually only depends upon genetics.

So for instance, if we consider blood type as an example of discontinuous variation, we will see that blood type can either be A or B or AB or O, and it is controlled by a single gene.

So there are no environmental or lifestyle influences that can impact upon your blood type.

It is specific and fixed to one gene.

Discontinuous variation where there might be a little bit more in variation, such as in eye colour, for instance, usually have two or more genes affecting the characteristic, but they are still genetic.

There's no environmental or lifestyle impact influencing those characteristics.

So the subtle variations in eye colour mean that there must be several genes controlling eye colour, but it's still only genes.

There's no environment and there's no lifestyle factors influencing them.

So how about this then? A feature with many discontinuous variations must be influenced by the environment.

True or false? Did you say false? Well done.

But can you justify your answer? Okay, did you say that the variation may be caused by several genes? Well done if you did.

Remembering that discontinuous variation is only caused by genes and not by environment or lifestyle.

So what I'd like you to do now is go to the data that you've plotted as a graph and analyse it and write a conclusion.

Your conclusion should describe the trends in the data, suggest what type of variation the data shows, whether it's continuous or discontinuous, suggest a cause for the variation and suggest what might not cause the variation.

So pause the video and come back to me when you're ready.

Okay, so with your data, you might have concluded something along the lines of this.

For instance, that seven students could not roll their tongue and of the remaining 23, 14 could twist their tongue into a straw and the other 9 could pucker their tongue.

This is an example of discontinuous variation, and because there are degrees of tongue puckering, the ability to roll your tongue may be controlled by two or more genes, but it is not affected by the environment or by lifestyle.

So just review your answer and see whether you've got similar features to mine.

Make any amendments if you need to, and reflect on how well you've done.

Well done indeed.

So in our lesson today, we have seen that discontinuous variation can be observed and plotted as a bar chart.

And bar charts display discontinuous data that is divided into categories with no in-between values.

And that's because discontinuous variation is caused by genetic factors only.

If there are many variations within a discontinuous feature, then it's likely that several genes are involved in influencing it rather than just one.

So thank you very much for joining me.

Well done for creating those graphs and drawing some really excellent conclusions from them.

That was good, but hard work.

I hope you enjoyed it.

I certainly did.

Thank you very much for joining me, and I hope to see you again soon, bye.