a graph that shows the distribution of a variable used to “summarize” data visually on a graph

HISTOGRAM• a graph that shows

the distribution of a variable

• used to “summarize” data visually on a graph

X-AXIS

• a single continuous variable broken into different intervals

• ~8-20 intervals

Y-AXIS

• the number of individuals in that interval

• “amount”, “frequency” or “percentage”

Die Roll

1 2 3 4 5 6

Height (cm)

130 140 150 160 170 180 190 200

Height (cm)

130 140 150 160 170 180 190 200

Height (cm)

130 140 150 160 170 180 190 200

Distribution Curve: a line drawn over the bars of a histogram to summarize patterns

Height (cm)

130 140 150 160 170 180 190 200

Normal Distribution: a distribution that is symmetrical around the mean

Height (cm)

130 140 150 160 170 180 190 200

Standard Deviation = 5 inchesStandard Deviation = 2 inches

Height (inches)

130 140 150 160 170 180 190 200

Standard Deviation: a measure of variance High Standard Deviation = High Variation

Low Standard Deviation = Low Variation

RIGHT SKEWED LEFT SKEWED

MEANMEDIAN

MODE

In a normal distribution,MEAN, MEDIAN, and MODE are centered in the middle

MEDIANMODE

MEANMEDIANMODE

MEAN MEDIAN MODE

In a skewed distribution,• the MODE is at the peak• the MEDIAN splits the area under the curve

in half• Area left of the median = Area right of the

median• the MEAN is in the direction of the skew

The MEAN is most influenced by the skew.

Within a species, there is usually a great deal of variation among

individuals.

Variation: is a measure of differences

INHERITED VARIATION

• results from the differences in DNA

• also known as “genetic variation”

• most inherited variation cannot be changed

• Examples: blood type, hair color, eye color, mid-digit hair, etc.

SOURCES OF GENETIC VARIATION

• Sexual Reproduction:genes mix when two parents create offspring

• Mutations:individual genes randomly mutate within an individual

ACQUIRED VARIATION

• results from differences in individual lifestyles

• does NOT affect your DNA

• does NOT get passed on to offspring

• Examples: muscle mass, obesity, hair dye, many skills

SOURCES OF ACQUIRED VARIATION

•the environment

North side, upper branches

South side, upper branches

North side, lower branches

South side, lower branches

The differences between apples are acquired during the growing season.

Difference will not be inherited.

Apples collected from different positions on the same tree.

• Most differences in an individual are the result of inherited and

acquired variations.

low variance high variance

Cheetahs , Manatees Leopards, Cuttlefish

• Populations prefer to have high variation to increase their chance of survival

• Having high levels of variationallow more potential for evolution

Clause Wedekind

1998 Bern

University in Switzerland

SWEATY SHIRT EXPERIMENT

49 men wore the same shirt for 2 days 44 women were asked to rank the shirts in order of smell

preference the scientists measured the MHC genes (genes related to

smell) of each male and each female the results found that women preferred shirt smells from

males who had the most different MHC genes from their own Women preferred males whose paired offspring would have

the greatest genetic variation