What happens in crossing over?

A. Exchange of genetic material between homologous chromosomes
B. Exchange of genes during metaphase of mitosis
C. Random distribution of chromosomes during meiosis
D. Homologous chromosomes fail to separate during meiosis

During which stage of meiosis does crossing over usually occur?

A. Prophase I

B. Metaphase I

C. Prophase II

D. Metaphase II

The diagram shows a pedigree chart.

What does it reveal about the inheritance of the blood disorder beta-thalassaemia?

A. The allele is autosomal recessive.
B. The allele is autosomal dominant.
C. The allele is sex-linked.
D. The allele is co-dominant.

Which structure found in eukaryotes has a single membrane?

A. Nucleus

B. Lysosome

C. Chloroplast

D. Mitochondrion