Complete Figure 3 by putting A or a in the boxes. One box has been completed for you with A.

Put a tick (✓) in the box next to the name of the process that produced the combination of alleles on the chromosome in the first polar body in Figure 3.

☐ Anaphase

☐ Crossing over

☐ Independent assortment

☐ Semi-conservative replication

A scientist measured the diameter of a polar body and the diameter of the nucleus inside it. The diameter of the polar body was 10.4 µm and the diameter of the nucleus was 7.0 µm. The density of mitochondria in the cytoplasm of the polar body (outside of the nucleus) was 0.08 mitochondria per µm3.

Calculate the number of mitochondria in the polar body. You should assume polar bodies and nuclei are spherical.

The formula for the volume of a sphere is 4/3 πr3 where π = 3.14

Show your working.

Number of mitochondria = ______________

Mitochondrial diseases are caused by faulty mitochondria. All of a person's mitochondria are inherited from their mother via the egg cell. An egg cell contains approximately 3 × 105 mitochondria.

One proposed treatment to prevent passing on faulty mitochondria involves • removing the nucleus from an egg cell donated by a woman with healthy mitochondria • replacing this nucleus with the contents of the polar body from a woman whose egg cells are affected by mitochondrial disease.

Suggest how this treatment prevents inheritance of mitochondrial diseases.

If most of the mitochondria in a cell are faulty, this prevents many important enzyme-catalysed reactions taking place or slows them down.

Suggest and explain one reason why.