Module 2 Variation - Lagan Biology Department



Module 2 Variation

Living organisms vary and this variation is influenced by genetic and environmental factors

A species is a group of organisms that are similar to each other but different from members of other species.

If members of one species differ from other species this is known as ____________________________________

If members of one species differ from each other than this is called ____________________________________.

In order to examine or make measurements of a species samples can be taken. Variation in sampling can come about in a couple of ways

Bias sampling – the investigator, knowingly or unknowingly, chooses samples

Chance – this is down to luck – even if the sampling is not biased the sample selected may not always be representative of the whole population.

In order to eliminate sampling bias, random sampling can be taken. When taking a random sample it is recommended:

1 that a large sample size is used. Explain why

_____________________________________________________________________________________________________________________________________________________________________________________________________________________

the results that are collected can be statistically analysed.

One method of random sampling is to use the following method

How to take random samples: (Learn this method)

| |

|Grid Segment (number-letter) |Number of Sunflowers |

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|Total Number of Sunflowers |

|Average per grid (divide total by 10) |

|Total number of plants in meadow (multiply average by 100) |

|Actual Data |

|Total number of Sunflowers ______ (count by hand) |

|Average number of Sunflowers (divide total by 100) Per grid _____ |

Analysis:

1. Compare the total number you got for sunflowers from the SAMPLING to the ACTUAL count.  How close are they? 

2. Why was the paper-slip method used to select the grid segments?

3. Why do biologists use Sampling?   Why can’t they just go into the forest and count all the sunflower plants?

4. Describe how you would use Sampling to determine the population of dandelions in your yard.

5. In a forest that measures 5 miles by 5 miles, a sample was taken to count the number of silver maple trees in the forest. The number of trees counted in the grid is shown below. The grids where the survey was taken were chosen randomly. Determine how many silver maple trees are in this forest using the random sampling technique. Show your work!

|  |7 |  |  |  |

|  |  |  |  |3 |

|  |  |  |5 |  |

|11 |  |9 |  |  |

|  |  |  |  |  |

What factors can cause variation?

Variation within the species is caused by two main factors – genetic factors or environmental factors or a mixture of both.

Examples of variation characteristics:

|Characteristic |Genetic |Environmental |Mixture of both |

|Shape of Nose | | | |

|Height | | | |

|Size of ears | | | |

|Shape of nose | | | |

|Colour of skin | | | |

|Natural hair colour | | | |

|Amount of tooth decay | | | |

|Freckles | | | |

|Strength | | | |

|Length of Hair | | | |

What causes genetic variation?

Genetic variation arises due to different genes that different individuals possess.

Genetic variation can result from

1. Mutation ______________________________________________________________________________________________________________________________________________

2. Meiosis

_____________________________________________________________________________________________________________________________________________

3. Fusion of gametes

_____________________________________________________________________________________________________________________________________________________________________________________________________________________

What is the only way that genetic variation can occur in asexual reproducing organisms

Environmental Influences causing variation

What environmental factors can affect variation?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Variation may be a result of a combination of both genetic and environmental conditions. An individual may have inherited the genetic information for a particular characteristic but environmental factors may affect the expression of that characteristic

For example – the skin colour is affected by the amount of melanin in the skin (genetic) but exposure to sunlight also has an influence (environmental)

Types of Variation

Variation in a population can be studied by measuring the characteristic (phenotype) in a large number of different individuals and by then plotting a frequency histogram. This graph has valued of the characteristic on the x axis and the number of individuals showing that characteristic on the y axis. These histograms show that there are two major types of variation – continuous and discontinuous.

The categories that are used are known as the frequency distribution e.g. colour of eye, heights.

If the data collected is in specific groups or categories of these are known as discrete categories e.g. eye colour – you can only have blue/brown eyes not a combination

Discrete data always is shown in a bar chart and shows discontinuous variation

• Discontinuous variations have distinct categories

• Tend to be quantitative with no overlap between categories

• Are controlled by one gene or a small number of genes

• Are largely unaffected by the environment.

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Examples of discrete variables = earlobes attached/detached, blood group, seed colour, flower colour.

If the data collected in numerical and is a range of value this is known as continuous variables and a frequency distribution curve is normally bell shaped (a line graph is drawn) The frequency histogram is a smooth curve (usually the bell-shaped normal distribution curve). Examples of continuous variation include height weight, shoe size

• There have no distinct categories into which individuals can be place

• Tend to be quantitative with overlaps between the categories

• Are controlled by a large number of genes (polygenic)

• Are affected by the environment

When looking at the frequency distribution in a graph information can be obtained

The mean ______________________________________________________________________________________________________________________________________________

Standard Deviation

_____________________________________________________________________________________________________________________________________________________________________________________________________________________

Problem In a survey of 30 students the following information was obtained

|Blood Group |Number of pupils |

|A |12 |

|B |1 |

|AB |2 |

|O |15 |

What type of variable is this information?

What type of graph would you draw?

|Biomass |Number of Pupils |

|50 – 52 |2 |

|53-55 |5 |

|56 – 58 |15 |

|59 – 61 |6 |

|62 – 64 |2 |

What type of variable is this information?

What type of graph would you draw?

Standard Deviation

Standard deviation is a measure of the spread of results at either side of the mean (average). It tells you how much the values in a single sample vary.

• These sets of data have the same mean (average).

• The data shows a normal distribution about the mean value – there is a bell-shaped and even distribution of values above and below the mean.

• The diagram on the left shows a smaller standard deviation, indicating there is less variation between individuals for the character mentioned.

• The diagram on the right shows a greater standard deviation, indicating there is greater variation.

Calculating Standard Deviation

Calculate the mean value ( )

Subtract the mean value ( ) from each of the measured values (x)

Square all the numbers ( )

Add the squared values together

Divide this by the number of measurements taken )n)

Square root this number

Standard Deviation, s =

The bean

Two students weighed samples of broad beans. One student obtained the data shown as Sample A and the other student obtained data Sample B

|Sample A (g) |Sample B (g) |

|1.42 |1.36 |

|1.42 |1.37 |

|1.43 |1.40 |

|1.44 |1.43 |

|1.44 |1.44 |

|1.44 |1.44 |

|1.44 |1.47 |

|1.45 |1.48 |

|1.46 |1.49 |

|1.46 |2.01 |

Calculate the Mean and Standard Deviation for the two samples

What can you conclude about the results.

The mean value tells you the average of the values and can be used to see if there is variation between samples. The standard deviation tells you how much the values in a single sample vary – it is a measure of the spread of values about the mean.

A large standard deviation means the values in the sample vary a lot.

The histogram shows the variation in height of 17-year-old male students from one college.

(a) What does the histogram indicate about the inheritance of this feature? Explain your answer.

.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2)

A biologist investigated the effect of the distance apart that parsnip seeds were planted on the number of seeds that germinated. Sets of 20 parsnip seeds were grown in trays. The seeds were set either touching each other or placed 2cm apart. The numbers of seeds in each set that had germinated after 10 days were recorded and displayed on a table of results

| Number of seeds that had germinated after 10days |

|Seeds touching each other |Seeds placed 2cm apart |

8 |10 |10 |5 |6 |12 |14 |16 |16 |12 |15 |16 | |15 |9 |13 |12 |9 |10 |10 |12 |13 |16 |12 |10 | |8 |10 |7 |10 |8 |7 |15 |11 |15 |14 |13 |13 | |14 |9 |11 |7 |9 |14 |11 |15 |14 |8 |13 |14 | |11 |10 |9 |12 |8 |9 |19 |11 |12 |17 |9 |17 | |

Calculate the mean and standard deviation for the two samples

Write a conclusion about the effect of planting the seeds

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