John Hay Biomedical · Week 5 · September 21 to 25, 2026

Week 5 figure sheet: PBS

The profile, the clock, and the two errors. Periods 1-2 and 6A-7B.

Figure 1. A DNA profile drawn as peaks

Four stacked capillary electrophoresis traces on a common size axis from about 60 to 360 base pairs, each in its own colour. D3S1358 in blue shows two peaks called 15 and 17. vWA in green shows two peaks called 16 and 18. FGA in amber shows two peaks called 22 and 24. Amelogenin in red shows two peaks called X and Y. The vertical axis on each trace is labelled RFU and runs past 2000.

How to read it

This is the same kind of DNA profile as a gel, drawn a second way, as peaks on a machine readout instead of bands. Each row is one STR locus, and the number printed under each peak is a repeat count. Amelogenin is not an identity locus: X and Y is the male pattern, and a single X is the female pattern. Part A does not use this figure. Part A uses the gel bands in the Case record on today's class page: compare your questioned lane with each reference lane, band by band.

What this figure does not supply

This figure does not supply a rarity figure, so it cannot tell you how strong a match is. The spacing between paired peaks is stretched for legibility, so read the allele NUMBERS, never the base-pair positions.

Figure 2. Body cooling after death

A line graph. The horizontal axis is hours after death from 0 to 24. The vertical axis is core temperature in degrees Celsius from about 20 to 37. The curve holds flat near 37 degrees for roughly the first three and a half hours, then falls steeply and almost straight until about 14 hours, then bends and flattens as it approaches a dashed horizontal line labelled ambient temperature at about 21 degrees, which it never reaches.

How to read it

Read the shape, not a single number. The temperature holds nearly flat at first, then falls steadily, then flattens again as it approaches the room. Find where the flat part ends and the steady fall begins.

What this figure does not supply

This figure does not supply a time of death. It shows one cooling curve under one set of conditions. Body size, clothing, covering, moving air and a wet or cold surface all change the rate, which is why an examiner uses adjusted tables rather than a single curve.

Figure 3. Three clocks, three schedules

A horizontal timeline from 0 to 48 hours with three labelled bands. Algor mortis begins at zero and continues across the whole timeline. Livor mortis begins at zero, with a divider marked fixed at twelve hours and a deeper tint after it. Rigor mortis rises from about three and a half hours, peaks at twelve hours, and fades out by thirty six hours.

How to read it

Each band is one postmortem change and the hours it covers. Read across to see which changes overlap at a given hour. Where all three bands agree is where your window sits.

What this figure does not supply

These are approximate ranges under average conditions, not fixed rules. Heat, cold and heavy activity before death all shift them. This figure does not supply your case's observations; those come from your own record.

Figure 4. The four outcomes of any test

A two by two table. Columns read condition present and condition absent. Rows read test positive and test negative. The four cells read true positive, false positive, false negative and true negative. Below the table two formulas are set as fractions: sensitivity equals T P over T P plus F N, and specificity equals T N over T N plus F P.

How to read it

Columns are what is actually true. Rows are what the test said. Read the cell where the two meet. The two formulas underneath show which cells each rate is built from.

What this figure does not supply

This figure does not supply any error rate for the Novel Flu Syndrome test in the debate case. None was given, so none may be invented or calculated.

Using these figures

Every figure here is a teaching illustration drawn for this course. Each one is accurate in the relationship it shows, and each caption names what it cannot tell you.

The rule that applies to all four

A figure narrows what is possible. It does not close a question. When you write a claim from any figure on this sheet, write the limit underneath it in the same breath: this shows ___, it does not show ___.

Generated 2026-09-21 for John Hay High School, Cleveland Metropolitan School District. Figures are original illustrations produced for this class and checked against the science they name before publication.