Griffin experimented with heat-killed S and R strain bacteria. He discovered that their offspring had the ability to develop pneumonia in mouses, even though none of the parental bacteria could cause that disease. When he injected both strains, the mouse developed pneumonia. Griffin isolated S as well as R strain bacteria from its blood. He concluded that heat-killed S strain bacteria passed on their genetic material to the offspring, so the harmless bacteria transformed into the type that causes pneumonia. He named the process transformation and concluded that gene was a transforming factor.

A. How do bacteria live in mice

In prophase I of a meiotic division, chromosomes are paired with the adequate homologous chromosome. In this phase occurs a crossover, which is an interchange of DNA material within the homologous chromosomes.

C. Duplicated chromosomes crossing-over

Three roles of the DNA molecule in heritage are in storage, copying and transmitting genes.
Deoxyribonucleic acid is made of nucleotides which are combined with covalent bonds and form a chain. Nucleotides consist of deoxyribose, the phosphate group, and a nitrogenous base (adenine, cytosine, thymine, and guanine).
A gene represents a sequence of nucleotides in a DNA molecule that contains information about coding a functional protein.

A. The sequences of nitrogenous bases