Alleles, genotype, and phenotype | Starter Quiz | Oak National Academy

Phenotype refers to an organism’s observable characteristics. Which factors can affect an organism’s phenotype?

• Its genetic code only.

• Its genetic code and its environment.

• Its environment only.

Answer explanation

Phenotypes are caused by an organism’s genes, but some are affected by the environment. For example, in humans, eye colour is wholly determined by genes but height is determined by genes and nutrition.

Starting with the smallest, put these in size order.

• Nucleus

• Chromosome

• Gene

• Nucleotide

Answer explanation

Nucleotides are joined together to form DNA. This is the genetic code. Genes are part of a very long DNA molecule that codes for a protein.

What is the genome in a unicellular organism?

• All the genes in the cell.

• All the non-coding DNA in the cell.

• All the DNA in the cell.

• All the proteins in the cell.

• All the enzymes in the cell.

Answer explanation

The genome is the total amount of DNA in a cell, whether this is in the nucleus or not.

Which is the best description of a DNA molecule?

• A polymer made of two nucleotide chains forming a double helix.

• A monomer made of one nucleotide chain forming a helix.

• A polymer made of one nucleotide chain forming a helix.

• A monomer made of two nucleotide chains forming a double helix.

• A polymer made of three nucleotide chains forming a triple helix.

Answer explanation

DNA is often described as a double helix because it is composed of two polynucleotide chains wrapped into a helix.

True or false? All genes code for enzymes.

• True

• False

Answer explanation

Genes carry the genetic code or instructions to enable a cell to produce proteins. Some proteins are structural (for example cellulose, which is found in plant cell walls), and others are functional, such as enzymes.

Put these in order to describe the production of a red pigment in a petal.

• The genetic code in a gene is copied.

• A red pigment is produced.

• Amino acids are joined together in sequence to make a polypetide chain.

• The chain folds up to make an enzyme.

• The enzyme speeds up a chemical reaction.

Answer explanation

The genetic code of a gene determines the amino acid sequence in an enzyme. The sequence of amino acids in the enzyme determines its three-dimensional folded shape, which in turn determines its ability to catalyse a reaction.